Programming .NET 3.5

Animation

The power of transformations is greatly enhanced when they are combined with animation. Rotate an object? Interesting. Rotate an object in front of my eyes? Much more interesting.

To be animated in WPF, an object must meet just three requirements:

• It must have a dependency property (see the upcoming sidebar "Dependency and Attached Properties").

• It must belong to a class that inherits from DependencyObject and implements IAnimatable (controls such as Button, Panel, and Shape all inherit from DependencyObject and implement IAnimatable, so this is almost never a problem).

• There must be a compatible animation type available (or you can create your own).

The typical first step for animation is to pick a property to animate. In the next example, you'll animate a Button's rotation by changing its angle. The Angle value is of type Double, so you'll use a DoubleAnimation to create a transition between the starting and ending values (referred to as the From and To properties). You must also specify a Duration—that is, the time it takes to go from the starting value to the destination value. The longer the Duration is, the slower the animation is.

The second step is to create a Storyboard, inside which you will place the DoubleAnimation. The DoubleAnimation designates where to apply the animation (the Storyboard.TargetName)—in other words, it specifies the object to animate (in this case, the button).

The final step is to associate the Storyboard with a Trigger (i.e., the event that will ...