Programming WPF, 2nd Edition

Where Are We?

You should write a custom element only if the underlying behavior you require is not offered by any of the built-in types, and you cannot build it by composing existing elements. Even if you do write a custom type, it will not necessarily be a control. When you write a custom element of any kind, you will use the dependency property system to provide properties that support data binding and animation. You will use the routed event infrastructure to expose events. If your element defines a particular interactive behavior, it should be a control. If you want to write a "lookless" control that allows its visuals to be replaced just like the built-in controls, you must consider how your control and template will interact with one another. You will also most likely want to supply a default style with a template that provides a default set of visuals.