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Archive for the ‘Windows Forms’ Category

Better Tool Support for .NET

Posted by Dan Vanderboom on September 7, 2009

Productivity Enhancing Tools

Visual Studio has come a long way since its debut in 2002.  With the imminent release of 2010, we’ll see a desperately-needed overhauling of the archaic COM extensibility mechanisms (to support the Managed Package Framework, as well as MEF, the Managed Extensibility Framework) and a redesign of the user interface in WPF that I’ve been pushing for and predicted as inevitable quite some time ago.

For many alpha geeks, the Visual Studio environment has been extended with excellent third-party, productivity-enhancing tools such as CodeRush and Resharper.  I personally feel that the Visual Studio IDE team has been slacking in this area, providing only very weak support for refactorings, code navigation, and better Intellisense.  While I understand their desire to avoid stepping on partners’ toes, this is one area I think makes sense for them to be deeply invested in.  In fact, I think a new charter for a Developer Productivity Team is warranted (or an expansion of their team if it already exists).

It’s unfortunately a minority of .NET developers who know about and use these third-party tools, and the .NET community as a whole would without a doubt be significantly more productive if these tools were installed in the IDE from day one.  It would also help to overcome resistance from development departments in larger organizations that are wary of third-party plug-ins, due perhaps to the unstable nature of many of them.  Microsoft should consider purchasing one or both of them, or paying a licensing fee to include them in every copy of Visual Studio.  Doing so, in my opinion, would make them heroes in the eyes of the overwhelming majority of .NET developers around the world.

It’s not that I mind paying a few hundred dollars for these tools.  Far from it!  The tools pay for themselves very quickly in time saved.  The point is to make them ubiquitous: to make high-productivity coding a standard of .NET development instead of a nice add-on that is only sometimes accepted.

Consider just from the perspective of watching speakers at conferences coding up samples.  How many of them don’t use such a tool in their demonstration simply because they don’t want to confuse their audience with an unfamiliar development interface?  How many more demonstrations could they be completing in the limited time they have available if they felt more comfortable using these tools in front of the masses?  You know you pay good money to attend these conferences.  Wouldn’t you like to cover significantly more ground while you’re there?  This is only likely to happen when the tool’s delivery vehicle is Visual Studio itself.  Damon Payne makes a similar case for the inclusion of the Managed Extensibility Framework in .NET Framework 4.0: build it into the core and people will accept it.

The Gorillas in the Room

CodeRush and Resharper have both received recent mention in the Hanselminutes podcast (episode 196 with Mark Miller) and in the Deep Fried Bytes podcast (episode 35 with Corey Haines).  If you haven’t heard of CodeRush, I recommend watching these videos on their use.

For secondary information on CodeRush, DXCore, and the principles with which they were designed, I recommend these episodes of DotNetRocks:

I don’t mean to be so biased toward CodeRush, but this is the tool I’m personally familiar with, has a broader range of functionality, and it seems to get the majority of press coverage.  However, those who do talk about Resharper do speak highly of it, so I recommend you check out both of them to see which one works best for you.  But above all: go check them out!

Refactor – Rename

Refactoring code is something we should all be doing constantly to avoid the accumulation of technical debt as software projects and the requirements on which they are based evolve.  There are many refactorings in Visual Studio for C#, and many more in third-party tools for several languages, but I’m going to focus here on what I consider to be the most important refactoring of them all: Rename.

Why is Rename so important?  Because it’s so commonly used, and it has such far-reaching effects.  It is frequently the case that we give poor names to identifiers before we clearly understand their role in the “finished” system, and even more frequent that an item’s role changes as the software evolves.  Failure to rename items to accurately reflect their current purpose is a recipe for code rot and greater code maintenance costs, developer confusion, and therefore buggy logic (with its associated support costs).

When I rename an identifier with a refactoring tool, all of the references to that identifier are also updated.  There might be hundreds of references.  In the days before refactoring tools, one would accomplish this with Find-and-Replace, but this is dangerous.  Even with options like “match case” and “match whole word”, it’s easy to rename the wrong identifiers, rename pieces of string literals, and so on; and if you forget to set these options, it’s worse.  You can go through each change individually, but that can take a very long time with hundreds of potential updates and is a far cry from a truly intelligent update.

Ultimately, the intelligence of the Rename refactoring provides safety and confidence for making far-reaching changes, encouraging more aggressive refactoring practices on a more regular basis.

Abolishing Magic Strings

I am intensely passionate about any tool or coding practice that encourages refactoring and better code hygiene.  One example of such a coding practice is the use of lambda expressions to select identifiers instead of using evil “magical strings”.  From my article on dynamically sorting Linq queries, the use of “magic strings” would force me to write something like this to dynamically sort a Linq query:

Customers = Customers.Order("LastName").Order("FirstName", SortDirection.Descending);

The problem here is that “LastName” and “FirstName” are oblivious to the Rename refactoring.  Using the refactoring tool might give me a false sense of security in thinking that all of my references to those two fields have been renamed, leading me to The Pit of Despair.  Instead, I can define a function and use it like the following:

public static IOrderedEnumerable<T> Order<T>(this IEnumerable<T> Source, 
    Expression<Func<T, object>> Selector, SortDirection SortDirection)
{
    return Order(Source, (Selector.Body as MemberExpression).Member.Name, SortDirection);
}

Customers = Customers.Order(c => c.LastName).Order(c => c.FirstName, SortDirection.Descending);

This requires a little understanding of the structure of expressions to implement, but the benefit is huge: I can now use the refactoring tool with much greater confidence that I’m not introducing subtle reference bugs into my code.  For such a simple example, the benefit is dubious, but multiply this by hundreds or thousands of magic string references, and the effort involved in refactoring quickly becomes overwhelming.

Coding in this style is most valuable when it’s a solution-wide convention.  So long as you have code that strays from this design philosophy, you’ll find yourself grumbling and reaching for the inefficient and inelegant Find-and-Replace tool.  The only time it really becomes an issue, then, is when accessing libraries that you have no control over, such as the Linq-to-Entities and the Entity Framework, which makes extensive use of magic strings.  In the case of EF, this is mitigated somewhat by your ability to regenerate the code it uses.  In other libraries, it may be possible to write extension methods like the Order method shown above.

It’s my earnest hope that library and framework authors such as the .NET Framework team will seriously consider alternatives to, and an abolition of, “magic strings” and other coding practices that frustrate otherwise-powerful refactoring tools.

Refactoring Across Languages

A tool is only as valuable as it is practical.  The Rename refactoring is more valuable when coding practices don’t frustrate it, as explained above.  Another barrier to the practical use of this tool is the prevalence of multiple languages within and across projects in a Visual Studio solution.  The definition of a project as a single-language container is dubious when you consider that a C# or VB.NET project may also contain HTML, ASP.NET, XAML, or configuration XML markup.  These are all languages with their own parsers and other language services.

So what happens when identifiers are shared across languages and a Rename refactoring is executed?  It depends on the languages involved, unfortunately.

When refactoring a C# class in Visual Studio, the XAML’s x:Class value is also updated.  What we’re seeing here is cross-language refactoring, but unfortunately it only works in one direction.  There is no refactor command to update the x:Class value from the XAML editor, so manually changing it causes my C# class to become sadly out of sync.  Furthermore, this seems to be XAML specific.  If I refactor the name of an .aspx.cs class, the Inherits attribute of the Page directive in the .aspx file doesn’t update.

How frequent do you think it is that someone would want to change a code-behind file for an ASP.NET page, and yet would not want to change the Inherits attribute?  Probably not very common (okay, probably NEVER).  This is a matter of having sensible defaults.  When you change an identifier name in this way, the development environment does not respond in a sensible way by default, forcing the developer to do extra work and waste time.  This is a failure in UI design for the same reason that Intellisense has been such a resounding success: Intellisense anticipates our needs and works with us; the failure to keep identifiers in sync by default is diametrically opposed to this intelligence.  This represents a fragmented and inconsistent design for an IDE to possess, thus my hope that it will be addressed in the near future.

The problem should be recognized as systemic, however, and addressed in a generalized way.  Making individual improvements in the relationships between pairs of languages has been almost adequate, but I think it would behoove us to take a step back and take a look at the future family of languages supported by the IDE, and the circumstances that will quickly be upon us with Microsoft’s Oslo platform, which enables developers to more easily build tool-supported languages (especially DSLs, Domain Specific Languages). 

Even without Oslo, we have seen a proliferation of languages: IronRuby, IronPython, F#, and the list goes on.  A refactoring tool that is hard-coded for specific languages will be unable to keep pace with the growing family of .NET and markup languages, and certainly unable to deal with the demands of every DSL that emerges in the next few years.  If instead we had a way to identify our code identifiers to the refactoring tool, and indicate how they should be bound to identifiers in other languages in other files, or even other projects or solutions, the tools would be able to make some intelligent decisions without understanding each language ahead of time.  Each language’s language service could supply this information.  For more information on Microsoft Oslo and its relationship to a world of many languages, see my article on Why Oslo Is Important.

Without this cross-language identifier binding feature, we’ll remain in refactoring hell.  I offered a feature suggestion to the Oslo team regarding this multi-master synchronization of a model across languages that was rejected, much to my dismay.  I’m not sure if the Oslo team is the right group to address this, or if it’s more appropriate for the Visual Studio IDE team, so I’m not willing to give up on this yet.

A Default of Refactor-Rename

The next idea I’d like to propose here is that the Rename refactoring is, in fact, a sensible default behavior.  In other words, when I edit an identifier in my code, I more often than not want all of the references to that identifier to change as well.  This is based on my experience in invoking the refactoring explicitly countless times, compared to the relatively few times I want to “break away” that identifier from all the code that references.

Think about it: if you have 150 references to variable Foo, and you change Foo to FooBar, you’re going to have 150 broken references.  Are you going to create a new Foo variable to replace them?  That workflow doesn’t make any sense.  Why not just start editing the identifier and have the references update themselves implicitly?  If you want to be aware of the change, it would be trivial for the IDE to indicate the number of references that were updated behind the scenes.  Then, if for some reason you really did want to break the references, you could explicitly launch a refactoring tool to “break references”, allowing you to edit that identifier definition separately.

The challenge that comes to mind with this default behavior concerns code that spans across solutions that aren’t loaded into the IDE at the same time.  In principle, this could be dealt with by logging the refactoring somewhere accessible to all solutions involved, in a location they can all access and which gets checked into source control.  The next time the other solutions are loaded, the log is loaded and the identifiers are renamed as specified.

Language Property Paths

If you’ve done much development with Silverlight or WPF, you’ve probably run into the PropertyPath class when using data binding or animation.  PropertyPath objects represent a traversal path to a property such as “Company.CompanyName.Text”.  The travesty is that they’re always “magic strings”.

My argument is that the property path is such an important construct that it deserves to be an core part of language syntax instead of just a type in some UI-platform-specific library.  I created a data binding library for Windows Forms for which I created my own property path syntax and type, and there are countless non-UI scenarios in which this construct would also be incredibly useful.

The advantage of having a language like C# understand property path syntax is that you avoid a whole class of problems that developers have used “magic strings” to solve.  The compiler can then make intelligent decisions about the correctness of paths, and errors can be identified very early in the cycle.

Imagine being able to pass property paths to methods or return then from functions as first-class citizens.  Instead of writing this:

Binding NameTextBinding = new Binding("Name") { Source = customer1; }

… we could write something like this, have access to the Rename refactoring, and even get Intellisense support when hitting the dot (.) operator:

Binding NameTextBinding = new Binding(@Customer.Name) { Source = customer1; }

In this code example, I use the fictitious @ operator to inform the compiler that I’m specifying a property path and not trying to reference a static property called Name on the Customer class.

With property paths in the language, we could solve our dynamic Linq sort problem cleanly, without using lambda expressions to hack around the problem:

Customers = Customers.Order(@Customer.LastName).Order(@Customer.FirstName, SortDirection.Descending);

That looks and feels right to me.  How about you?

Summary

There are many factors of developer productivity, and I’ve established refactoring as one of them.  In this article I discussed tooling and coding practices that support or frustrate refactoring.  We took a deep look into the most important refactoring we have at our disposal, Rename, and examined how to get the greatest value out of it in terms of personal habits, as well as long-term tooling vision and language innovation.  I proposed including property paths in language syntax due to its general usefulness and its ability to solve a whole class of problems that have traditionally been solved using problematic “magic strings”.

It gives me hope to see the growing popularity of Fluent Interfaces and the use of lambda expressions to provide coding conventions that can be verified by the compiler, and a growing community of bloggers (such as here and here) writing about the abolition of “magic strings” in their code.  We can only hope that Microsoft program managers, architects, and developers on the Visual Studio and .NET Framework teams are listening.

Posted in Data Binding, Data Structures, Design Patterns, Development Environment, Dynamic Programming, Functional Programming, Language Innovation, LINQ, Oslo, Silverlight, Software Architecture, User Interface Design, Visual Studio, Visual Studio Extensibility, Windows Forms | Leave a Comment »

Control Invoke Pattern Using Lambdas

Posted by Dan Vanderboom on July 1, 2008

In Windows Forms development, there are often times when you need to update the user interface in response to something happening on another thread.  This could be a timer firing every second, some service running in the background and notifying the client of updated status on its own (background) thread, etc.  If you’ve been working with Windows Forms for any length of time, you’ve doubtless run into exceptions that kindly inform you that you can’t update controls on a thread other than the one that created those controls. We’ll consider the simple issue of a timer firing every second, and the display of elapsed time in a label, for our example here, and introduce a new pattern to make this cleaner and more intuitive.

First we’ll set up our start time and the thread.  I use the System.Threading.Timer to ensure that we’re using a non-UI thread.

StartTime = DateTime.Now;

Timer = new System.Threading.Timer(new TimerCallback(Timer_Tick));
Timer.Change(0, 1000);

Here’s the event handler that calculates the elapsed time and calls Invoke, as well as the method we’re invoking, which will run on the UI thread, where it can safely update the lblElapsedTime label control.

private void Timer_Tick(object state)
{
    TimeSpan ts = DateTime.Now - StartTime;
    Invoke(new StringDelegate(DisplayText), ts.TotalSeconds.ToString());
}

private void DisplayText(string Text)
{
    lblElapsedTime.Text = Text;
}

In order to make this work, we need the event handler, a separate method to run in the UI thread, and also a delegate that matches the invoked method.

public delegate void StringDelegate(string Text);

This is a lot of moving parts for such a small piece of functionality.  To make matters worse, you may need to repeat this pattern many times, depending on the controls (or combinations thereof) that you need to update.  In a modern multi-threaded application, your class can become littered with these invocations, handlers, and delegates.

What I’d really like to do is call Invoke and pass in an anonymous method (in lambda form).  Unfortunately, Invoke takes a Delegate parameter, which is an abstract type.  This forces you to instantiate a concrete delegate type.  So while we eliminate our need for a separate method, we’re still dependent on our delegate type.

private void Timer_Tick(object state)
{
    TimeSpan ts = DateTime.Now - StartTime;
    Invoke(new StringDelegate(s => lblElapsedTime.Text = s), ts.TotalSeconds.ToString());
}

Or are we?  By using the Action (or MethodInvoker) delegate for all of these invocations, and relying on C# and its support for closures, we can make a reference to the TimeSpan variable from within the anonymous method body, like this:

private void Timer_Tick(object state)
{
    TimeSpan ts = DateTime.Now - StartTime;
    Invoke(new Action(() => lblElapsedTime.Text = ts.TotalSeconds.ToString()));
}

Here it’s contained within a single method, and no additional delegates will be necessary to make this work.  That’s pretty nice!  (A similar approach is taken here.)  But it’s still not quite as slick and intuitive as I’d like.  By creating an extension method, adding another overload of Invoke to the Control class, we can allow Invoke to assume a concrete Action delegate class, and write code like this:

private void Timer_Tick(object state)
{
    TimeSpan ts = DateTime.Now - StartTime;
    this.Invoke(() => lblElapsedTime.Text = ts.TotalSeconds.ToString());
}

Now that’s clean.  Just call Invoke, and pass in the lambda to execute.  Or several statements in a code block if you like.  It’s very succinct.  The only part that bothers me is the this keyword that’s required.  Extension methods don’t register in Intellisense, nor do they compile successfully, if they’re used without a variable, this, base, or something else with a dot after them.  If we’re really going to push the illusion of extending a class, I think we need to go all the way and make it work without having to explicitly type this.  But it is what it is for now; hopefully this will be fixed in the next version of C# (along with adding support for extension properties, events, and operators).

That being said, here is the extension method to make this work:

public static void Invoke(this Control Control, Action Action)
{
    Control.Invoke(Action);
}

It couldn’t be simpler (thanks to a little help from Mads Torgersen)!  I’ll include the finished program for those of you who want to run it to see and experiment; you’ll just need to create the Program.cs with the startup code yourself.  Create a new Windows Forms app and use what’s there, renaming the form listed in Application.Run to match this one.

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Threading;

namespace ControlInvokeLambda
{
    public partial class frmTestInvokeLambda : Form
    {
        private Button btnExit;
        private Label lblElapsedTime;

        // make sure we're using the Threading Timer for our example, which runs on a non-UI thread
        private System.Threading.Timer Timer;
        
        private DateTime StartTime;

        public frmTestInvokeLambda()
        {
            // initialize controls
            
            btnExit = new Button();
            btnExit.Location = new Point(88, 80);
            btnExit.Name = "btnExit";
            btnExit.Size = new Size(118, 26);
            btnExit.TabIndex = 0;
            btnExit.Text = "Exit";
            btnExit.UseVisualStyleBackColor = true;
            btnExit.Click += new EventHandler(this.btnExit_Click);

            lblElapsedTime = new Label();
            lblElapsedTime.AutoSize = true;
            lblElapsedTime.Location = new Point(140, 36);
            lblElapsedTime.Name = "lblElapsedTime";
            lblElapsedTime.Size = new Size(13, 13);
            lblElapsedTime.TabIndex = 1;
            lblElapsedTime.Text = "0";

            AutoScaleDimensions = new SizeF(6F, 13F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(292, 136);
            Controls.Add(lblElapsedTime);
            Controls.Add(btnExit);
            Name = "frmTestInvokeLambda";
            Text = "Invoke Lambda";
            PerformLayout();

            // remember start time and startup timer

            StartTime = DateTime.Now;

            Timer = new System.Threading.Timer(new TimerCallback(Timer_Tick));
            Timer.Change(0, 1000);
        }

        private void btnExit_Click(object sender, EventArgs e)
        {
            Timer.Change(Timeout.Infinite, Timeout.Infinite);
            Application.Exit();
        }

        private void Timer_Tick(object state)
        {
            TimeSpan ts = DateTime.Now - StartTime;
            this.Invoke(() => lblElapsedTime.Text = ts.TotalSeconds.ToString());
        }
    }

    public static class ControlExtensions
    {
        public static void Invoke(this Control Control, Action Action)
        {
            Control.Invoke(Action);
        }
    }
}

Posted in Algorithms, Concurrency, Design Patterns, Windows Forms | 2 Comments »

Compact Framework Controls (Part 3): Linear Gradients

Posted by Dan Vanderboom on May 5, 2008

[This article is part of a series that starts in this article and precedes this one here.]

Linear Gradients

Linear gradients are a nice, subtle effect that can turn a boring control into something more interesting and professional looking.  You can use a linear gradient for the entire background of your control, which I’ll demonstrate in this article, or you can paint one or more regions selectively to display a gradient.  A linear gradient is a gradual transition from one color to another, and while you can transition through multiple colors along an axis, going from blue to red to green to white to black if you wanted, I’m going to start simple and create a control that blends between only two colors.  You can also define the line of change to be any angle: vertical (as shown in the example below), horizontal, or some other angle.  I’ll show how to draw just the vertical and horizontal linear gradients.

Linear Gradient Example

I’ll be using the control from my previous article, and adding to it, to demonstrate linear gradients.  We’re going to need some new properties to support gradients, so first we need to add a couple enumerations.

public enum RegionFillStyle
{
    SolidColor,
    LinearGradient
}

public enum LinearGradientDirection
{
    Horizontal,
    Vertical
}

And now the new properties.

private RegionFillStyle _FillStyle = RegionFillStyle.SolidColor;
[DefaultValue(RegionFillStyle.SolidColor)]
public RegionFillStyle FillStyle
{
    get { return _FillStyle; }
    set { _FillStyle = value; Refresh(); }
}

private LinearGradientDirection _LinearGradientDirection = LinearGradientDirection.Vertical;
[DefaultValue(LinearGradientDirection.Vertical)]
public LinearGradientDirection LinearGradientDirection
{
    get { return _LinearGradientDirection; }
    set { _LinearGradientDirection = value; Refresh(); }
}

private Color _BackColor2 = Color.White;
public Color BackColor2
{
    get { return _BackColor2; }
    set { _BackColor2 = value; Refresh();  }
}

The goal is to draw a background for our control that is a linear gradient, fading from BackColor to BackColor2.  We’re going to use a technique called interpolation, which is the calculation of new data points based on the values of adjacent data points.  In our case, we’re going to be interpolating color values.  We know the color at the top and the bottom (in the case of a vertical gradient), so a pixel halfway between them spatially should have a color value that is halfway between the color values at both ends.  Because colors are manipulated in bitmaps with an RGB scheme (using red, blue, and green aspects), we actually have three component values that need to be interpolated.

Understanding the Math

If our control is 100 pixels tall, and the color at the bottom is 100 units less blue than at the top, the translation is very simple: as we move down each pixel from top to bottom, we’ll subtract 1 unit of color from the blue value.  The challenge lies in the fact that we can’t assume our height and our color values will line up so nicely.  Furthermore, we have two other colors to deal with, and they may need to change at different rates or in different directions: the color may become slightly more red while simultaneously becoming drastically less green.

So we’re going to need some way of finding the scaling factor between the height or width of the control and the distance in color values for red, green, and blue separately.  In our example of 100 pixels to 100 color units, we have a 1:1 scaling factor.  If we instead had to make a color change of 200 units, we’d have a scaling factor of 1:2, or 1 pixel for 2 units of color change.  Another way to think of this is to say that for every pixel we move along the line, we’re going to increase or decrease our color by 2 units.

double RedScale = (double)Height / (BackColor2.R - BackColor.R);

The RedScale variable divides our height by our gradient’s difference (or change) in redness, and we make the same scaling calculation with green and blue.  This scaling takes increasing and decreasing color changes into account based on whether the subtraction expression on the right results in a positive or negative number.  As we move along the y axis, we’ll create a color that uses BackColor as a base and adds RGB values to it that divide the current y position with this scaling factor.  Let’s take a look at that code:

Bitmap LinearGradient = null;

if (LinearGradientDirection == LinearGradientDirection.Vertical)
{
    double RedScale = (double)Height / (BackColor2.R - BackColor.R);
    double GreenScale = (double)Height / (BackColor2.G - BackColor.G);
    double BlueScale = (double)Height / (BackColor2.B - BackColor.B);

    LinearGradient = new Bitmap(1, Height);
    for (int y = 0; y < Height; y++)
    {
        int red = BackColor.R + (int)((double)y / RedScale;
        int green = BackColor.G + (int)((double)y / GreenScale;
        int blue = BackColor.B + (int)((double)y / BlueScale;

        Color color = Color.FromArgb(red, green, blue);
        LinearGradient.SetPixel(0, y, color);
    }
}

if (LinearGradient != null)
{
    FillBrush = new TextureBrush(LinearGradient);
}

After calculating our scaling factors, we define a bitmap that’s as tall as our control, but only one pixel wide.  You can see this bitmap being used to create a TextureBrush at the bottom of the code.  This brush will be used to fill the entire area from left to right, copying the bitmap across the entire surface, so there’s no need to make it any wider than a single pixel.  (For horizontal gradients, we do the opposite: create a bitmap as wide as our control but only one pixel tall.)

In our hypothetical 100-pixel-tall control, with a red value that decreases 200 units from top to bottom (and therefore has a scaling factor of -0.5), we calculate each pixel’s redness by dividing y by -0.5.  At pixel y=25, which is 25% of the way down, we get a value of -50, which is 25% of -200.  At pixel y=75, we get 75 / -0.5 = -150.  So we take our original BackColor.R, and add this negative number, which makes it decrease from the base color as desired.

The only thing we need to do now is to ensure that each of our three color values never go outside the range of 0 to 255, otherwise we’ll get an error thrown from the Bitmap class.  We can do this with the Math class’s methods Min and Max, like this:

int red = Math.Max(Math.Min(BackColor.R + (int)((double)y / RedScale), 255), 0);
int green = Math.Max(Math.Min(BackColor.G + (int)((double)y / GreenScale), 255), 0);
int blue = Math.Max(Math.Min(BackColor.B + (int)((double)y / BlueScale), 255), 0);

Min returns the smaller of two numbers, and since we pass in 255 along with our calculated color, if our calculation is over 255, then the value it will return is 255.  Max does the opposite, and the combination ensures we stay within the valid range.

Results

The code sample above only showed the code for a vertical gradient, so here is the complete listing of our control with the logic for horizontal gradients as well.

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Drawing;
using System.Reflection;
using System.ComponentModel;

namespace CustomControlsDemo
{
    public class ClippingControl : Control
    {
        private RegionFillStyle _FillStyle = RegionFillStyle.SolidColor;
        [DefaultValue(RegionFillStyle.SolidColor)]
        public RegionFillStyle FillStyle
        {
            get { return _FillStyle; }
            set { _FillStyle = value; Refresh(); }
        }
        
        private LinearGradientDirection _LinearGradientDirection = LinearGradientDirection.Vertical;
        [DefaultValue(LinearGradientDirection.Vertical)]
        public LinearGradientDirection LinearGradientDirection
        {
            get { return _LinearGradientDirection; }
            set { _LinearGradientDirection = value; Refresh(); }
        }
        
        private Color _BackColor2 = Color.White;
        public Color BackColor2
        {
            get { return _BackColor2; }
            set { _BackColor2 = value; Refresh(); }
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            // define a canvas for the visual content of the control
            Bitmap MyBitmap = new Bitmap(Width, Height);
            Graphics g = Graphics.FromImage(MyBitmap);

            Brush FillBrush = null;
            if (FillStyle == RegionFillStyle.SolidColor)
            {
                FillBrush = new SolidBrush(BackColor);
            }
            else if (FillStyle == RegionFillStyle.LinearGradient)
            {
                Bitmap LinearGradient = null;

                if (LinearGradientDirection == LinearGradientDirection.Horizontal)
                {
                    double RedScale = (double)Width / (BackColor2.R - BackColor.R);
                    double GreenScale = (double)Width / (BackColor2.G - BackColor.G);
                    double BlueScale = (double)Width / (BackColor2.B - BackColor.B);

                    LinearGradient = new Bitmap(Width, 1);
                    for (int x = 0; x < Width; x++)
                    {
                        int red = Math.Max(Math.Min(BackColor.R + (int)((double)x / RedScale), 255), 0);
                        int green = Math.Max(Math.Min(BackColor.G + (int)((double)x / GreenScale), 255), 0);
                        int blue = Math.Max(Math.Min(BackColor.B + (int)((double)x / BlueScale), 255), 0);

                        Color color = Color.FromArgb(red, green, blue);
                        LinearGradient.SetPixel(x, 0, color);
                    }
                }
                else if (LinearGradientDirection == LinearGradientDirection.Vertical)
                {
                    double RedScale = (double)Height / (BackColor2.R - BackColor.R);
                    double GreenScale = (double)Height / (BackColor2.G - BackColor.G);
                    double BlueScale = (double)Height / (BackColor2.B - BackColor.B);

                    LinearGradient = new Bitmap(1, Height);
                    for (int y = 0; y < Height; y++)
                    {
                        int red = Math.Max(Math.Min(BackColor.R + (int)((double)y / RedScale), 255), 0);
                        int green = Math.Max(Math.Min(BackColor.G + (int)((double)y / GreenScale), 255), 0);
                        int blue = Math.Max(Math.Min(BackColor.B + (int)((double)y / BlueScale), 255), 0);

                        Color color = Color.FromArgb(red, green, blue);
                        LinearGradient.SetPixel(0, y, color);
                    }
                }

                if (LinearGradient != null)
                {
                    FillBrush = new TextureBrush(LinearGradient);
                }
            }

            if (FillBrush != null)
            {
                g.FillRectangle(FillBrush, ClientRectangle);
            }

            // draw graphics on our bitmap
            g.DrawLine(new Pen(Color.Black), 0, 0, Width - 1, Height - 1);
            g.DrawEllipse(new Pen(Color.Black), 0, 0, Width - 1, Height - 1);

            // dispose of the painting tools
            g.Dispose();

            // paint the background to match the Parent control so it blends in
            e.Graphics.FillRectangle(new SolidBrush(Parent.BackColor), ClientRectangle);

            // define the custom shape of the control: a trapezoid in this example
            List<Point> Points = new List<Point>();
            Points.AddRange(new Point[] { new Point(20, 0), new Point(Width - 21, 0), 
                new Point(Width - 1, Height - 1), new Point(0, Height - 1) });

            // draw that content inside our defined shape, clipping everything that falls outside of the region;
            // only if the image is much smaller than the control does it really get "tiled" and act like a textured painting brush
            // but our bitmap image is the same size as the control, so we're just taking advantage of clipping
            Brush ImageBrush = new TextureBrush(MyBitmap);

            e.Graphics.FillPolygon(ImageBrush, Points.ToArray());
        }
    }
}

Placing a couple of these controls on a form, I can set one of them to use a solid background (yellow), and the others to use vertical and horizontal linear gradients.

Linear Gradient Control Screenshot

Conclusion

Linear gradients are a great effect to have in your repertoire of techniques.  Compact Framework applications especially tend to be flat and dull, with an unimpressive array of built-in controls, and with more focus on user interfaces like the iPhone and some of the cool new HTC touch devices, the desire for fancier interfaces is growing.  As we start to mix operations like polygon clipping and quasi-transparency (presented in the previous article), linear gradients, and others, we can put together a bag of tricks for composing beautiful and interesting user experiences.

Posted in Algorithms, Compact Framework, Custom Controls, User Interface Design, Windows Forms | 9 Comments »

Compact Framework Controls (Part 2): Polygon Clipping

Posted by Dan Vanderboom on May 4, 2008

[This article is part of a series that starts in this article.]

My intention is to cover a full spectrum of activities around custom control development, with an emphasis on the compromises, workarounds, and special care that must be taken when developing controls for the Compact Framework.  In my first article, I talked about how most design-time attributes must be applied to control classes and their members, and what some of those attributes mean.  I have a number of articles planned that explore those attributes more, and will go into extending the design-time experience in more depth, but I’m going to take a detour into custom painting of the control surface first, so we have a control to reference and work with in the examples.

Polygon Clipping

If you’re new to creating graphical effects and unfamiliar with the techniques invovlved, clipping refers to the chopping off of an image based on some kind of border or boundary.  In Windows Forms interfaces, controls are inherently rectangular because clipping occurs automatically at the window’s boundary (which is a shame considering how this presumption of need slows rendering, and WPF takes good advantage of not doing so).  Everything outside the control’s outer shape doesn’t get drawn at all.  You can draw anywhere you want, including negative coordinates, but only the points that fall within the clipping region will be displayed.

Clipping Illustration

But what if you want to make your control a different shape, other than the standard rectangle, like an ellipse or a rounded rectangle?  How do you make sure that whatever you draw inside never leaks outside of your defined shape?  In the full .NET Framework, there is a Region property in the Control class that defines these boundaries, and there are several good articles that explain this.  The clipping mask is applied based on that Region’s definition.  In Compact Framework, the Region property doesn’t exist, and you’re forced to find your own way of defining different shapes.

The key to this is to understand the Graphics class’s Fill methods.  While FillEllipse and FillRectangle definitely have their uses, I’d like to focus on situations that are a little bit more demanding, such as when you want to represent a more complex shape like a rounded rectangle (with many points) or some kind of UML diagram element.  FillPolygon takes a list of Points, and with them can define the most eccentric and specific of shapes.  By filling a polygon with an image using a TextureBrush, clipping happens automatically as part of the operation.

Let’s take a look at some code to see how we perform each of these steps: preparing and drawing on a bitmap image in memory, defining our shape’s boundaries, and then clipping that image within the specified shape.

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Drawing;
using System.Reflection;

namespace CustomControlsDemo
{
    public class ClippingControl : Control
    {
        protected override void OnPaint(PaintEventArgs e)
        {
            // define a canvas for the visual content of the control
            Bitmap MyBitmap = new Bitmap(Width, Height);

            // create a painting tools object
            Graphics g = Graphics.FromImage(MyBitmap);

            // draw graphics on our bitmap
            g.FillRectangle(new SolidBrush(Color.PaleGoldenrod), ClientRectangle);
            g.DrawLine(new Pen(Color.Black), 0, 0, Width - 1, Height - 1);
            g.DrawEllipse(new Pen(Color.Black), 0, 0, Width - 1, Height - 1);

            // dispose of the painting tools
            g.Dispose();

            // define the custom shape of the control: a trapezoid in this example
            List<Point> Points = new List<Point>();
            Points.AddRange(new Point[] { new Point(20, 0), new Point(Width - 21, 0), 
                new Point(Width - 1, Height - 1), new Point(0, Height - 1) });

            // draw that content inside our defined shape, clipping everything that falls outside of the region;
            // only if the image is much smaller than the control does it really get "tiled" and act like a textured painting brush
            // but our bitmap image is the same size as the control, so we're just taking advantage of clipping
            Brush ImageBrush = new TextureBrush(MyBitmap);
            e.Graphics.FillPolygon(ImageBrush, Points.ToArray());
        }
    }
}

Although this control has a silly shape and doesn’t do much yet, it does illustrate the basics of painting within the bounds of an irregular shape.  As long as we draw on MyBitmap, everything will be properly clipped by the call to FillPolygon.  However, as you can see in the screenshots below, the white background around our custom shape could be a problem.  You can change the BackColor property to match the color of the container its on (a Panel control in this case, which is Color.BurlyWood), but really it makes more sense for BackColor to describe the color within our shape.  We’d like the surrounding background to blend in with whatever container the control is sitting in.

first version

We can accomplish this with two simple changes.  First, at some point before the FillPolygon call, we need to fill the entire control’s area with the BackColor property of the parent control.  We will draw using the e.Graphics object, which paints on the whole rectangular control, not our g Graphics object, whose contents get clipped.  Then, instead of hard coding Color.PaleGodenrod, we can use the BackColor property to specify our fill color.  Here is the changed section of code:

// draw graphics on our bitmap
g.FillRectangle(new SolidBrush(BackColor), ClientRectangle);
g.DrawLine(new Pen(Color.Black), 0, 0, Width - 1, Height - 1);
g.DrawEllipse(new Pen(Color.Black), 0, 0, Width - 1, Height - 1);

// dispose of the painting tools
g.Dispose();

e.Graphics.FillRectangle(new SolidBrush(Parent.BackColor), ClientRectangle);

Now if we set the BackColor to PaleGodenrod, we’ll get this rendering:

transparent background

Dragging the control off the panel and into the white area will cause the area around the control to paint white, so now you can see how it blends in with whatever background we have as long as it’s a solid color.

In a future article, after I’ve covered how to draw arcs and curves, I will revisit this technique and demonstrate how to draw rectangles with rounded corners.

[This article is part of a series that continues in this article.]

Posted in Algorithms, Compact Framework, Custom Controls, User Interface Design, Visual Studio, Windows Forms, Windows Mobile | 12 Comments »

Using Extension Methods to Manipulate Control Bitmaps in Compact Framework

Posted by Dan Vanderboom on April 11, 2008

I’m loving extension methods.  All of the methods that I wish BCL classes had, I can now add.  While I consider it highly unfortunate that we can’t yet add extension properties, events, or static members of any kind, still it’s a great amount of power in terms of making functionality discoverable in ways not possible before.

During the implementation of my Compact Framework application’s MVC framework, I wanted to support displaying views modally.  However, using a screen stack of UserControls that are all hosted in a single master Form object, I lose out on this built-in functionality and so found myself in need of creating this behavior myself.  One of the difficulties in doing this is displaying a view that may not cover every portion of other views beneath it; if the user clicks on one of the views “underneath”, that control gets activated, and if pressed on a control, that control will handle the event (such as Button.Click).

My solution to the problem is simple.  Take a snapshot of the master form and everything on it, create a PictureBox control that covers the whole form and bring it to front, and set its image to the snapshot bitmap.  Doing this provides the illusion that the user is still looking at the same form full of controls, and yet if they touch any part of the screen, they’ll be touching a PictureBox that just ignores them.  The application is then free to open a new view UserControl on top of that.  When the window is finally closed, the MVC infrastructure code tears down the PictureBox, and the real interface once again becomes available for interaction.

Screenshots before and after screen capture and darkening

In addition, I wanted the ability to emphasize the modal view, so you can see from the picture above that I decided to accomplish this by de-emphasizing the background bitmap.  By darkening the snapshot, the pop-up modal view really does seem to pop out.  The only problem with bitmap manipulation using the Compact Framework library is that it’s extremely slow, but I get around this by using some unsafe code to manipulate the memory region where the bitmap image gets mapped.  (If you’re unfamiliar with the unsafe keyword, don’t worry: this code actually is safe to use.)

Here is the full source code for taking a snapshot of a form (or any control), as well as adjusting the brightness.

using System;
using System.Linq;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public static class ControlBitmapExtensions
{
    [DllImport("coredll.dll")]
    private static extern bool BitBlt(IntPtr hdc, int nXDest, int nYDest, int nWidth, int nHeight,
        IntPtr hdcSrc, int nXSrc, int nYSrc, int dwRop);

    public struct PixelData
    {
        public byte Blue;
        public byte Green;
        public byte Red;
    }

    public static Bitmap GetSnapshot(this Control Control)
    {
        Rectangle rect = new Rectangle(0, 0, Control.Width, Control.Height - 1);
        Graphics g = Control.CreateGraphics();
        Bitmap Snapshot = new Bitmap(rect.Width, rect.Height);
        Graphics gShapshot = Graphics.FromImage(Snapshot);
        BitBlt(gShapshot.GetHdc(), 0, 0, rect.Width, rect.Height, g.GetHdc(), rect.Left, rect.Top, 0xCC0020);
        gShapshot.Dispose();

        return Snapshot;
    }

    public static unsafe Bitmap AdjustBrightness(this Bitmap Bitmap, decimal Percent)
    {
        Percent /= 100;
        Bitmap Snapshot = (Bitmap)Bitmap.Clone();
        Rectangle rect = new Rectangle(0, 0, Bitmap.Width, Bitmap.Height);

        BitmapData BitmapBase = Snapshot.LockBits(rect, ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
        byte* BitmapBaseByte = (byte*)BitmapBase.Scan0.ToPointer();

        // the number of bytes in each row of a bitmap is allocated (internally) to be equally divisible by 4
        int RowByteWidth = rect.Width * 3;
        if (RowByteWidth % 4 != 0)
        {
            RowByteWidth += (4 - (RowByteWidth % 4));
        }

        for (int i = 0; i < RowByteWidth * rect.Height; i += 3)
        {
            PixelData* p = (PixelData*)(BitmapBaseByte + i);

            p->Red = (byte)Math.Round(Math.Min(p->Red * Percent, (decimal)255));
            p->Green = (byte)Math.Round(Math.Min(p->Green * Percent, (decimal)255));
            p->Blue = (byte)Math.Round(Math.Min(p->Blue * Percent, (decimal)255));
        }

        Snapshot.UnlockBits(BitmapBase);
        return Snapshot;
    }

    public static Bitmap Brighten(this Bitmap Bitmap, decimal PercentChange)
    {
        return AdjustBrightness(Bitmap, 100 + PercentChange);
    }

    public static Bitmap Darken(this Bitmap Bitmap, decimal PercentChange)
    {
        return AdjustBrightness(Bitmap, 100 - PercentChange);
    }
}

 

Because Control is extended by GetSnapshot, and Bitmap is extended by AdjustBrightness, Brighten, and Darken, I can write very clear and simple code like this on the consuming side:

Bitmap bitmap = MyForm.GetSnapshot().Darken(40);

…and voila!  I have a snapshot.  Note that because Darken extends Bitmap, it can now be used with any Bitmap.  As we read from this code from left to right, we’re observing a pipeline of transformations.  MyForm is the source data, GetSnapshot is the first step, Darken is the next change, and with more extension methods on Bitmap we could continue to process this in a way that is very natural to think about and construct.

I do have to admit that I cheated a little, though.  Even with the direct memory manipulation with pointers, it still didn’t perform very well on the Symbol and DAP devices I tested on.  So instead of adjusting the brightness on every pixel, I only darken every third pixel.  They’re close enough together that you can’t really tell the difference; however, the closer to 100 percent you darken or brighten an image, the more apparent the illusion will be, since two thirds of the pixels won’t be participating.  So it’s good for subtle effects, but I wouldn’t count on it for all scenarios.

This every-third-pixel dirty trick happens in the for loop, where you see i += 3, so go ahead and experiment with it.  Just be careful not to set it to large even numbers or you’ll end up with stripes!

Posted in Algorithms, Compact Framework, Object Oriented Design, Problem Modeling, User Interface Design, Windows Forms, Windows Mobile | 5 Comments »

Compact Framework Controls (Part 1): Creating Custom Controls and Designers

Posted by Dan Vanderboom on March 14, 2008

I’ve been having a lot of fun learning how to create rich design-time experiences for custom controls in Compact Framework for the past few days.  It’s been frustrating, and the documentation is hard to find unless you’re already familiar with the metaphors and know the buzzwords.  While this first article won’t be completely comprehensive, I will continue to write about this topic until I have covered all of the bases necessary for you to create professional, polished controls and design-time experiences suitable for commercial use or sale.

I’m going to assume you have at least some experience in creating custom controls, at least for desktop applications.  Creating custom controls for Compact Framework applications is another story, however.  Not because of any particular constraints of memory of screen real estate, but because the typical method for attaching metadata to specify design-time behavior is different.  There are some other subtleties and oddness as well that are specific to the Compact Framework.

In the full .NET Framework, we have many attributes at our disposal to specify design-time behavior; most of these can be found in System.ComponentModel.  We have access to a lot of these for mobile device applications, but because they’re not included in the Compact Framework, we need another way to associate them with our control classes and their members.  This is done through something called the “design-time attributes file”, which has an extension of .xtma.

There are two ways to add this file.  The method that people typically suggest is to add a class diagram to your project (right-click on your project in Solution Explorer, and select View Class Diagram), select an item in the diagram, edit the Custom Attributes property in the property grid (see screenshot below), click on the ellipsis (…) to open a pop-up window, and then enter an attribute such as DesktopCompatible(true).

Custom Attributes in properties

When you click the OK button, a new file will be added to your project called DesignTimeAttributes.xtma, and this file will open in Visual Studio.

This is quite a round-about way to create the file in my opinion, and it presumes that you know a valid attribute to add right from the beginning.  I personally don’t use the class diagrams, and I think it’s easier just to add the .xtma file directly, by right-clicking on your project in Solution Explorer, Add—New Item, and selecting Design-Time Attribute File.  Editing your attributes directly in this XML file instead of the pop-up window in the class designer has the benefit of providing you with some Intellisense (which it gets from the associated XSD file).

I get a little disappointed when I see people list only the most common attributes that I already know about, and then fail to mention the rest of the attributes that are supported in Compact Framework, and since the list isn’t unmanagable—and easily determined from Intellisense—I will list most of them that are supported .xtma file here, and in a future artile will provide the remaining ones.

Here’s a screenshot showing the full list of tags that you can use at the class level.  Most of them are attributes, while some of them like Event, Method, and Property allow you to specify specific members of the class so that you can apply attributes to just those members.

 Xtma attributes

This is what they mean:

  • ApplyDeviceDefaults – I couldn’t find any mention of this in the normal area of MSDN that enumerates all of the classes, but I did find it explained well in this MSDN article.
  • ComplexBindingProperties – For complex data binding, of course.
  • DefaultBindingProperty – This is for simple data binding.
  • DefaultEvent – The default event for Button is Click.  When you double-click on a control in the designer, Visual Studio switches to the code behind file and will automatically generate this event’s handler for you.  Very handy.
  • DefaultProperty – When you select a control in the designer, this is the property in the properties window that gets focus first.  For the Label control, this is the Caption property.
  • Description – The description text appears in the properties window below the grid of property names and values, and can provide useful information about the meaning of a property or event.
  • Designer – The Designer attribute is one of the primary gateways for providing rich design-time experiences for your controls.  Creating custom designers and associating your controls with them is a tricky business, and one I intend to explore in depth in this and future articles.  Because MSDN documentation in this area is rather sparse, I’ve begun contributing to the community content on the MSDN pages, and you’ll see the help I’ve added at the very bottom of the page if you follow the link for this item.
  • DesignerSerializer – Located in System.ComponentModel.Design.Serialization, a DesignerSerializer is used to provide a custom way of serializing your control to code in the designer partial class file.  I haven’t had a need yet to use this, but if someone can think of a real-world scenario that requires it, I will be happy to explore the subject further and write about it.
  • DesignTimeVisible – Indicates whether a control can be shown on a designer, and is supposedly ignored by “components with a UI presense”, whatever that means.  A little more usefully, MSDN states that it is useful when you have a control that accepts child components, such as the TreeView whose node items “should not appear in the component tray because they are drawn by the TreeView control”.  This will require some more exploration.
  • DesktopCompatible – This is the first design-time attribute I became familiar with in working with Compact Framework controls.  If you have a control that makes P/Invoke calls, Visual Studio is uncertain whether they’re device specific OS calls, and to be safe, it doesn’t execute your control’s code, which means your control can’t render itself even on the designer surface.  You get a message telling you that it’s unsafe.  To get around this, and presuming that it is indeed safe to run your control’s code on the desktop (I’ll explain more about this later, or you can read this article by XinYan), just add a DesktopCompatible attribute to the control class, and you’ll be back in business.  I’m not sure where this attribute is located; it’s not a desktop attribute, so it’s not in the full .NET Framework’s System.dll, and a search through Reflector didn’t locate it, so I’ll have to keep looking.  But it’s there, and it works.
  • Docking – Specifies the default docking behavior for controls.  This is located in System.Windows.Forms.
  • Editor – If you need a more powerful experience for editing complex properties within the properties window itself, this attribute will allow you to hook into one.  I’ll be covering over custom editors in detail.
  • ImmutableObject – Specifies that an object has no subproperties capable of being edited, per MSDN documentation.  Not sure what the benefits of that would be: perhaps to hide all properties for a class without having to hide each one separately?
  • InitializationEvent – This is used to support auto data-binding (by Visual Studio wizards I’m guessing), so it knows which event to hook into when generating the data-binding code.
  • LookupBindingProperties
  • RootDesignerSerializer – I’m not sure what this was for originally, but according to bug report, this attribute is both deprecated and broken.
  • Supported – Explained in this blog as part of Platform Verification Task.  Located in Microsoft.CompactFramework.Build.Tasks.  You can use this attribute to indicate that a class or member is not supported for the specific platform.
  • SuppressFiltering – Located in Microsoft.CompactFramework.Build.Tasks.
  • ToolboxBitmap – This simply specifies the bitmap that will be displayed in the toolbox.  Located in System.Drawing.
  • TypeConverter – Specifies the TypeConverter class used for a property.  TypeConverters are an important aspect of the design-time experience and merit further explanation.
  • Browsable – This determines whether a property or event will be displayed in the properties window, and is typically used to hide properties or events that must be public for some reason but aren’t meant to be manipulated during design time.
  • Category – If you set this to an existing category name, your property or event will appear in there; if you create your own category name, a new category will appear in the properties window.

There are a few more that are specific to properties, events, and methods, but this will give us a good start.  I’ll cover the remainder in future articles.

That seems like a lot at first glance, but chances are that you’ll only need a handful at any given time.  With a little exploration and practice (and guidance from myself and others whose blogs and other resources I’ll share), you could soon be a master of rich, no-compromise custom control development for Compact Framework applications.  I believe this is a worthy cause, for one because there is a scarcity of good third-party controls, especially when compared to the abundance that we have for the desktop world of .NET development; but also because I have personally struggled with Compact Framework development and have always thought it would be nice to have a step-by-step series of tutorial to follow for creating custom controls.  I’ve found many useful and helpful articles, but nothing that really brings it all together in a clear manner.

Here is an example .xtma file for a new user control I created that has Category and Description attributes on a property I created called HighlightForeColor:

XTMA

The magic happens when you build your custom control project.  Visual Studio builds not only your control project in its runtime form, but also generates another assembly with .asmmeta.dll after your own target assembly name.

Build output

If you use Reflector to disassemble it, you will see that this is a design-time component that contains all of your classes and their members with real attributes attached.  Strangely, it does not contain any code, and parameters have no names.  The purpose is simply to be a carrier of attributes.  This is a screen shot from Reflector, showing the attached attributes:

Reflector

I’m puzzled by this implementation detail.  Attributes are so insignificant in size, being just metadata tags.  If Microsoft had just included them in the Compact Framework, it seems they could have avoided the requirement for this second, oddly-empty assembly (and there is a third, for custom designers and editors, as you’ll see later).  Unless there’s something else to it that I’m missing…

[This article is part of a series that continues in this article.]

Posted in Compact Framework, Custom Controls, User Interface Design, Visual Studio, Windows Forms, Windows Mobile | 10 Comments »

Windows Forms Data Binding: Language-Level Support Needed

Posted by Dan Vanderboom on March 6, 2008

I’ve been busy building an MVC framework for the past few weeks, and one of the aspects of this framework I want to make as transparent as possible is data binding.  I want to use automatic data binding between a control property in the view and a property in the controller.  This is much more difficult than it needs to be.  Because my controller inherits from a base class, it has access to a helper method to raise the PropertyChanged event in the INotifyPropertyChanged interface, which makes things a tad easier.

LastNameProperty

Here is what that helper method looks like:

SetProperty

Even with a code snippet to generate the property (with the call to SetProperty), I don’t like it.  For one or two properties, it’s not too bad, but when you have dozens of properties that need to notify another object of changes—multiplied by dozens of controllers and views, it creates code bloat.  The string “LastName”, lacking strong typing, is also less than perfect.

What I really want is to combine automatic properties (a new feature in C# 3.0) with a new language keyword like “notify” that would hook the SetProperty logic into the setter.  Like this:

public notify string LastName { get; set; }

The same keyword for collection types, producing slightly different notification effects, would be nice as well, so I wouldn’t have to use BindingList<T> specifically.

public notify List<Customer> Customers { get; set; }

But alas, I’ll have to do it the hard way.  I’ve been considering using an aspect weaver to stitch in this logic in a post-build task.  It would work, but the notifications wouldn’t be fired during debugging, and that’s just not acceptable.

Data binding is extremely important, and WPF has—from what I’ve seen so far—done a great job implementing it.  For those of us stuck in Windows Forms (I develop applications for Windows Mobile devices primarily), some other alternatives are long overdue.

I’ve been able to mimic a small part of the capabilities of WPF data binding, specifically support for binding paths such as “Controller.Computer.ProcessorName”.  In Windows Forms data binding, if you change which object Controller.Computer points to, your user interface control will continue to reference the old Computer object’s ProcessorName property.  Not so good!  Using data binding paths, if you point Controller.Computer to a new Computer object, the UI control does an automatic rebinding to the new object’s ProcessorName property.  I then set the control’s Tag property to tell it the name of the control property and the name of the property to bind it to, like this: “Text=Controller.Customer.LastName”.  There have been a number of road blocks to making it work smoothly (such as dealing with null values, and null parent objects), but it does in fact work, is smooth and fast, and supports complex as well as simple data binding.

In a future blog post, I’ll describe the general design and hopefully also share some code.

Posted in Compact Framework, Data Binding, Invention-A-Day, Object Oriented Design, User Interface Design, Windows Forms | Leave a Comment »

 
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