Pro WPF in C# 2010: Windows Presentation Foundation in .NET 4

15.2. Basic Animation

You've already learned the first rule of WPF animation—every animation acts on a single dependency property. However, there's another restriction. To animate a property (in other words, change its value in a time-dependent way), you need to have an animation class that supports its data type. For example, the Button.Width property uses the double data type. To animate it, you use the DoubleAnimation class. However, Button.Padding uses the Thickness structure, so it requires the ThicknessAnimation class.

This requirement isn't as absolute as the first rule of WPF animation, which limits animations to dependency properties. That's because you can animate a dependency property that doesn't have a corresponding animation class ...