Dependency Property assigned with value binding does not work

Question

I have a usercontrol with a dependency property.

public sealed partial class PenMenu : UserControl, INotifyPropertyChanged
{
    public event PropertyChanged         


        

Answer 1

The getter and setter of a dependency property are not guaranteed to be run, and in particular the WPF binding engine / XAML processor is documented to bypass these. Have a look on MSDN - the getter/setter should just be a wrapper around GetValue/SetValue on the DependencyProperty itself.

Instead of reacting in the setter of your property, you should add a property changed handler in the original call to DependencyProperty.Register, when you can act on the new value.

(see other questions).

Answer 2

It's frustrating isn't it? First, include a changed event handler. Like this:

public string Title
{
    get { return (string)GetValue(TitleProperty); }
    set { SetValue(TitleProperty, value); }
}
public static readonly DependencyProperty TitleProperty =
    DependencyProperty.Register("Title", typeof(string), 
    typeof(MyControl), new PropertyMetadata(string.Empty, Changed));
private static void Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var c = d as MyControl;
    // now, do something
}

Then, please read this article so you see there are more gotchas than just that one: http://blog.jerrynixon.com/2013/07/solved-two-way-binding-inside-user.html

Best of luck!