How do You Create a Read-Only Dependency Property?

Question

How do you create a read-only dependancy property? What are the best-practices for doing so?

Specifically, what's stumping me the most is the fact that there's no implementation of

DependencyObject.GetValue()   

that takes a System.Windows.DependencyPropertyKey as a parameter.

System.Windows.DependencyProperty.RegisterReadOnly returns a DependencyPropertyKey object rather than a DependencyProperty. So how are you supposed to access your read-only dependency property if you can't make any calls to GetValue? Or are you supposed to somehow convert the DependencyPropertyKey into a plain old DependencyProperty object?

Advice and/or code would be GREATLY appreciated!

Answer 1

It's easy, actually (via RegisterReadOnly):

public class OwnerClass : DependencyObject // or DependencyObject inheritor {     private static readonly DependencyPropertyKey ReadOnlyPropPropertyKey         = DependencyProperty.RegisterReadOnly(             nameof(ReadOnlyProp),             typeof(int), typeof(OwnerClass),             new FrameworkPropertyMetadata(default(int),                 FrameworkPropertyMetadataOptions.None));      public static readonly DependencyProperty ReadOnlyPropProperty         = ReadOnlyPropPropertyKey.DependencyProperty;      public int ReadOnlyProp     {         get { return (int)GetValue(ReadOnlyPropProperty); }         protected set { SetValue(ReadOnlyPropPropertyKey, value); }     }      //your other code here ... } 

You use the key only when you set the value in private/protected/internal code. Due to the protected ReadOnlyProp setter, this is transparent to you.