How do You Create a Read-Only Dependency Property?

.net, dependency-properties, wpf

Solution

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.

Problem

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 D`ependencyPropertyKey` 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!

Original source