/// <summary>
/// Tries to get a value from a <see cref="DependencyProperty"/> that is stored somewhere in the visual tree above this <see cref="DependencyObject"/>.
/// If this is not available, it will register a <see cref="XAMLMarkupExtensions.Base.ParentChangedNotifier"/> on the last element.
/// </summary>
/// <typeparam name="T">The return type.</typeparam>
/// <param name="target">The <see cref="DependencyObject"/>.</param>
/// <param name="property">A <see cref="DependencyProperty"/> that will be read out.</param>
/// <param name="parentChangedAction">The notification action on the change event of the Parent property.</param>
/// <param name="parentNotifiers">A dictionary of already registered notifiers.</param>
/// <returns>The value, if possible.</returns>
public static T GetValueOrRegisterParentNotifier <T>(
this DependencyObject target,
DependencyProperty property,
Action <DependencyObject> parentChangedAction,
ParentNotifiers parentNotifiers)
{
return(target.GetValueOrRegisterParentNotifier(depObj => depObj.GetValueSync <T>(property), parentChangedAction, parentNotifiers));
}
/// <summary>
/// Tries to get a value that is stored somewhere in the visual tree above this <see cref="DependencyObject"/>.
/// <para>If this is not available, it will register a <see cref="ParentChangedNotifier"/> on the last element.</para>
/// </summary>
/// <typeparam name="T">The return type.</typeparam>
/// <param name="target">The <see cref="DependencyObject"/>.</param>
/// <param name="GetFunction">The function that gets the value from a <see cref="DependencyObject"/>.</param>
/// <param name="ParentChangedAction">The notification action on the change event of the Parent property.</param>
/// <param name="parentNotifiers">A dictionary of already registered notifiers.</param>
/// <returns>The value, if possible.</returns>
public static T GetValueOrRegisterParentNotifier <T>(
this DependencyObject target,
Func <DependencyObject, T> GetFunction,
Action <DependencyObject> ParentChangedAction,
ParentNotifiers parentNotifiers)
{
var ret = default(T);
if (target == null)
{
return(ret);
}
var depObj = target;
var weakTarget = new WeakReference(target);
while (ret == null)
{
// Try to get the value using the provided GetFunction.
ret = GetFunction(depObj);
if (ret != null && parentNotifiers.ContainsKey(target))
{
parentNotifiers.Remove(target);
}
// Try to get the parent using the visual tree helper. This may fail on some occations.
#if !SILVERLIGHT
if (!(depObj is Visual) && !(depObj is Visual3D) && !(depObj is FrameworkContentElement))
{
break;
}
if (depObj is Window)
{
break;
}
#endif
DependencyObject depObjParent = null;
#if !SILVERLIGHT
if (depObj is FrameworkContentElement)
{
depObjParent = ((FrameworkContentElement)depObj).Parent;
}
else
{
try { depObjParent = depObj.GetParent(false); }
catch { depObjParent = null; }
}
#endif
if (depObjParent == null)
{
try { depObjParent = depObj.GetParent(true); }
catch { break; }
}
// If this failed, try again using the Parent property (sometimes this is not covered by the VisualTreeHelper class :-P.
if (depObjParent == null && depObj is FrameworkElement)
{
depObjParent = ((FrameworkElement)depObj).Parent;
}
if (ret == null && depObjParent == null)
{
// Try to establish a notification on changes of the Parent property of dp.
if (depObj is FrameworkElement && !parentNotifiers.ContainsKey(target))
{
var pcn = new ParentChangedNotifier((FrameworkElement)depObj, () =>
{
var localTarget = (DependencyObject)weakTarget.Target;
if (!weakTarget.IsAlive)
{
return;
}
// Call the action...
ParentChangedAction(localTarget);
// ...and remove the notifier - it will probably not be used again.
if (parentNotifiers.ContainsKey(localTarget))
{
parentNotifiers.Remove(localTarget);
}
});
parentNotifiers.Add(target, pcn);
}
break;
}
// Assign the parent to the current DependencyObject and start the next iteration.
depObj = depObjParent;
}
return(ret);
}
