Animate Button size, then revert to null - windows-phone-7

Question

I am trying to create an animation to make it look like a button turns over and the back shows. So what I was trying to do is:
1- Show a button with BackgroundColor x. (The button now has a Width of null, the property ActualWidth does have a value.)
2- Create a double animation that changes the width of the button to zero.
DoubleAnimation widthAnimation = new DoubleAnimation();
widthAnimation.From = this.ActualWidth;
widthAnimation.To = 0;
widthAnimation.SpeedRatio = 3;
widthAnimation.Duration = TimeSpan.FromMilliseconds(800);
3- Change the BackgroundColor of the button.
ColorAnimation colorAnimation = new ColorAnimation();
colorAnimation.From = State ? _xColor : _yColor;
colorAnimation.To = State ? _yColor : _xColor;
colorAnimation.BeginTime = TimeSpan.FromMilliseconds(400);
colorAnimation.Duration = TimeSpan.Zero;
4- Change the width back to it's original value.
widthAnimation.AutoReverse = true;
The problem is when the animation runs twice the animation reads this.ActualWidth while animating, which causes it to fail to the original width. How can I solve this? I would like to set the Width back to null again, but it seems impossible to me.

Answer 1

You'd better use xaml style and template to "declare" what you want and let WPF/Silverlight take care of all.
If you try to do the same thing by code you can do it but you need to know what the framework does behind the scenes.
Basically you can set
- Style to define the values of some properties of the control
- DataTemplate to define the visual representation of the control's content
- ControlTemplate to define the appearance of the control
Each of those can have Triggers
- Property Triggers
to set properties or starts actions, such as an animation
when a property value changes or when an event is raised;
EventTriggers and Storyboards
to start a set of actions based on the occurrence of an event
If you like to learn about XAML Style and Template,
take a look at http://msdn.microsoft.com/en-us/library/ms745683.aspx
Spend a day to learn and save many hours (or days) of try and error and frustration!
To go right to the point, in your case I think you should use a Storyboard.
See http://msdn.microsoft.com/en-us/library/ms742868.aspx
where you can find also the code equivalent of XAML examples

Answer 2

I came to the idea to targetting the MaxWidth instead of the actual Width. I now use a KeyFrameCollection which sets the MaxWidth to int.MaxValue at the start (so also at the end when using autoreverse).
It will work fine untill there will be phones with a resolution bigger than the max int value.
The code:
DoubleAnimationUsingKeyFrames widthAnimation = new DoubleAnimationUsingKeyFrames();
widthAnimation.KeyFrames.Add(new DiscreteDoubleKeyFrame()
{
KeyTime = TimeSpan.Zero,
Value = int.MaxValue,
});
widthAnimation.KeyFrames.Add(new LinearDoubleKeyFrame()
{
KeyTime = TimeSpan.FromMilliseconds(1),
Value = ActualWidth,
});
widthAnimation.KeyFrames.Add(new LinearDoubleKeyFrame()
{
KeyTime = TimeSpan.FromMilliseconds(400),
Value = 0,
});
widthAnimation.Duration = TimeSpan.FromMilliseconds(400);
widthAnimation.AutoReverse = true;