Howcome get / set in dependency property does nothing?

Question

I created the dependency property as follows:

public partial class MyControl: UserControl { //... public static DependencyProperty XyzProperty = DependencyProperty.Register("Xyz",typeof (string),typeof (MyControl),new PropertyMetadata(default(string))); public string Xyz { get { return (string) GetValue(XyzProperty ); } set { SetValue(XyzProperty , value); } } //... } 

Then bind it to my wpf window and everything works fine.

When I tried to add some logic to the installer, I noticed that it was not called. I change get: set to the point now they look like this:

  get{return null;} set{} 

And it still works! How so? What causes the use of this GetValue / SetValue?

Answer 1

The WPF data binding infrastructure directly uses DependencyProperty, the Xyz property is a convenient interface for the programmer.

Take a look at PropertyMetadata in the DependencyProperty.Register call, you can specify the callback that will be executed when the property value changes, this is where you can apply your business logic.

Answer 2

DependencyProperty is the repository for XyzProperty. If you access a property through the DependencyProperty interface, it completely bypasses the Get / Set property receiver.

Think of it this way:

 private int _myValue = 0; public int MyValue { get { return _myValue; } set { _myValue = value; } } 

In this case, if I manually set _myValue = 12 , it is obvious that the Install accessory for the MyValue property will not be called; I completely went around it! The same applies to DependencyProperties. The WPF binding system uses DependencyProperty interfaces directly.