C# Programming > Windows Forms

Fading Windows Form in C#

Fading Form

A C# Windows Form can be programmed to have an effect of fading in and fading out using transperancy settings. The actual C# code is not very complex, it just needs to be structured properly.

The fade is done with a simple loop of Form's Opacity property:

for (double i = this.Opacity; i <= 1; i += fadeRate)
{
     ChangeOpacity(i);
}

if (this.Opacity != 1.00)
     ChangeOpacity(1.00);

Why does the C# code call ChangeOpacity instead of simply settings this.Opacity to a number? The short answers is because the application uses multithreading.

Multithreading

To avoid conflict the rest of the UI elements, multithreating is necessary. Multithreading will run the fading effects on a separate thread from the rest of the C# interface in order to avoid strange behavior.

What can that cause problems? The fading C# functions and the Windows Form will be in seperate threads. The newer .Net Framework version do not allow cross-thread calls.

The way around it is to use delegates. The C# function above use the call ChangeOpacity, which will create a delegate to access the Form's Opacity within its same thread:

private delegate void ChangeOpacityDelegate(double value);
private void ChangeOpacity(double value)
{
     if (this.InvokeRequired)
     {
          ChangeOpacityDelegate del = new ChangeOpacityDelegate(ChangeOpacity);
          object[] parameters = { value };

          this.Invoke(del, value);
     }
     else
     {
          //Your code goes here, in this case:
          this.Opacity = value;
     }
}

Notice that you can call any C# function you want and pass whatever parameters it needs.

C# Mouse Events

You will need only two C# mouse events, MouseEnter and MouseLeave. To call the Fade In and Fade Out C# functions, you will need this simple source code:

ThreadStart fadeInStart = new ThreadStart(FadeIn);
fadeIn = new Thread(fadeInStart);
fadeIn.Start();

Of course for the Fade Out function replace the FadeIn part.

There is one small problem. The Form's MouseLeave event will be fired when the cursor "leaves" the C# Form by "entering" another control, even though it is inside the Form. The simple work around is to add the following C# code at the beginning of the MouseLeave event:

if (this.Bounds.Contains(Cursor.Position)) return;

Avoiding Overflow

A quick note, you want to make sure you stop all running FadeIn FadeOut C# calls before calling another one. The reason for this is to avoid overflowing the stack, which can lead to the application crashing. Simply use the Abort C# call.

Check out how the Fading Form came out by download the example C# source code...

Download Fading Form C# Source Code

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