wpf Dependency Properties Read-only dependency properties
Example
When to use
A read-only dependency property is similar to a normal dependency property, but it is structured to not allow having its value set from outside the control. This works well if you have a property that is purely informational for consumers, e.g. IsMouseOver or IsKeyboardFocusWithin.
How to define
Just like standard dependency properties, a read-only dependency property must be defined on a class that derives from DependencyObject.
public class MyControl : Control
{
private static readonly DependencyPropertyKey MyPropertyPropertyKey =
DependencyProperty.RegisterReadOnly("MyProperty", typeof(int), typeof(MyControl),
new FrameworkPropertyMetadata(0));
public static readonly DependencyProperty MyPropertyProperty = MyPropertyPropertyKey.DependencyProperty;
public int MyProperty
{
get { return (int)GetValue(MyPropertyProperty); }
private set { SetValue(MyPropertyPropertyKey, value); }
}
}
The same conventions that apply to regular dependency properties also apply here, but with two key differences:
- The
DependencyPropertyis sourced from aprivateDependencyPropertyKey. - The CLR property setter is
protectedorprivateinstead ofpublic.
Note that the setter passes MyPropertyPropertyKey and not MyPropertyProperty to the SetValue method. Because the property was defined read-only, any attempt to use SetValue on the property must be used with overload that receives DependencyPropertyKey; otherwise, an InvalidOperationException will be thrown.
