WPF provides an innovative feature called attached properties, which can be used to add behavior to existing controls. These new properties are not defined on the control being extended, but rather they are defined on a separate object (generally a
DependencyObject). Thus, we end up with a source object that defines the attached properties and a target object on which you attach these properties. The target is the object being extended with new functionality contained in the source. When the attached property is set on the target object, a property change event is fired on the source. The event handler is passed information about the target and the new and old values of the property.
By hooking up property changed handlers, we can add additional behavior by calling methods on the target, changing properties, and listening to events. We look at more detailed examples of using attached properties in Chapter 6, “The Power of Attached Properties.” Keep in mind that…
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