>>Hi,
>>I have created a custom attached dependency property:

>>    public class CMProp : DependencyObject
>>    {
>>        public static readonly DependencyProperty ControlModeProperty;
>>
>>        static CMProp()
>>        {
>>            FrameworkPropertyMetadata fm = new FrameworkPropertyMetadata();
>>            fm.Inherits = true;
>>            fm.DefaultValue = ControlMode.Display;
>>            ControlModeProperty = DependencyProperty.RegisterAttached("ControlMode", typeof(LLControls.ControlMode), typeof(CMProp), fm);
>>        }
>>
>>        public static void SetControlMode(UIElement element, LLControls.ControlMode value)
>>        {
>>            element.SetValue(ControlModeProperty, value);
>>        }
>>
>>        public static LLControls.ControlMode GetControlMode(UIElement element)
>>        {
>>            return (LLControls.ControlMode)element.GetValue(ControlModeProperty);
>>        }
>>     }

ControlMode is an enum with three values: Display, HeaderEdit and DataEdit. I am using the dependency property on a sub-classed canvas:

public static readonly DependencyProperty ControlModeProperty;
>>static LLCanvas()
>>{
>>FrameworkPropertyMetadata p5 = new FrameworkPropertyMetadata();
>>p5.Inherits = true;
>>ControlModeProperty = CMProp.ControlModeProperty.AddOwner(typeof(LLCanvas), p5);
>>}

In use these canvases can be nested so, for example:
>>CanvasA
>>-->CanvasB
>>---->CanvasC
>>
>>If I set the ControlMode on CanvasA this flows through and is inherited by CanvasB and CanvasC as expected. If, however I set the ControlMode on CanvasB then, obviously, since I have set a local value there then subsequent changes on CanvasA are not inherited (which is fine).
>>But if I set the ControlMode of CanvasB to ControlMode.Display I want it to return to using the inherited value of CanvasA.
>>AFAICS I can't do this in the CoerceValue callback. I also tried using ClearValue() in the PropertyChanged callback but that doesn't appear to work either.
>>
>>Any suggestions on how to accomplish this?
>>TIA,
>>Viv
>
>
>I would if I could - you're way ahead

Not far enough :-{
I've solved it for now by changing the command handler that I use to set ControlMode from a context menu. e.g.:

void cbEditData_Executed(object sender, ExecutedRoutedEventArgs e)
{
     LLCanvas lla = MethodToGrabCurrentCanvas();
     MenuItem mi = e.Parameter as MenuItem;
     if (mi != null)
     {
          if (mi.IsChecked)
               lla.ControlMode = ControlMode.DataEdit;
          else
              ((DependencyObject)lla).ClearValue(CMProp.ControlModeProperty);
    }
}

but it feels like a kludge - there should be some way of doing this within the dependency property callbacks......