Introducing .NET 4.0: with Visual Studio 2010

14.10. Attached and Dependency Properties

When you set a property of an object in ASP.NET such as Width on a TextBox, you would usually write something like this:

<asp:TextBox Width="300" Runat="server" />

Behind the scenes, the Width value is retained in a private field. If you were to retrieve the Width property, it would be the same as when it was first set. However, when working with dependency properties, this is not necessarily true.

Consider how a browser works out where to display an item on the screen. It is not as straightforward as it first sounds. There are actually a number of things that need to be taken into account when calculating where an item will be positioned on a page:

• Other elements on the page

• Runtime settings (e.g., screen ...