WPF Concepts—Dependency Properties

Microsoft .NET Framework, ASP.NET, Visual C# (CSharp, C Sharp, C-Sharp) Developer Training, Visual Studio

Dependency Properties

WPF introduces a new type of property called a dependency property, used throughout the platform to enable styling, automatic data binding, animation, and more. You might first meet this concept with skepticism, as it complicates the picture of .NET types having simple fields, properties, methods, and events. But after you understand the problems that dependency properties solve, you will likely accept them as a welcome addition.

A dependency property depends on multiple providers for determining its value at any point in time. These providers could be an animation continuously changing its value, a parent element whose property value trickles down to its children, and so on. Arguably the biggest feature of a dependency property is its built-in ability to provide change notification.

The motivation for adding such intelligence to properties is to enable rich functionality directly from declarative markup. The key to WPF's declarative-friendly design is its heavy use of properties. Button, for example, has 96 public properties! Properties can be easily set in XAML (directly or by a design tool) without any procedural code. But without the extra plumbing in dependency properties, it would be hard for the simple action of setting properties to get the desired results without writing additional code.

In this section, we'll briefly look at the implementation of a dependency property to make this discussion more concrete, and then we'll dig deeper into some of the ways that dependency properties add value on top of plain .NET properties:

• Change notification

• Property value inheritance

• Support for multiple providers

Understanding most of the nuances of dependency properties is usually only important for custom control authors. However, even casual users of WPF end up needing to be aware of what they are and how they work. For example, you can only style and animate dependency properties. After working with WPF for a while you might find yourself wishing that all properties would be dependency properties!