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Finding an ancestor of a WPF dependency object

This is a simple snippet which helps you to find a specified parent of a given WPF dependency object somewhere in its visual tree:

(Snippet updated 2009.09.14)

/// <summary>

/// Finds a parent of a given item on the visual tree.

/// </summary>

/// <typeparam name="T">The type of the queried item.</typeparam>

/// <param name="child">A direct or indirect child of the

/// queried item.</param>

/// <returns>The first parent item that matches the submitted

/// type parameter. If not matching item can be found, a null

/// reference is being returned.</returns>

public static T TryFindParent<T>(this DependencyObject child)

    where T : DependencyObject

{

  //get parent item

  DependencyObject parentObject = GetParentObject(child);

  //we've reached the end of the tree

  if (parentObject == null) return null;

  //check if the parent matches the type we're looking for

  T parent = parentObject as T;

  if (parent != null)

  {

    return parent;

  }

  else

  {

    //use recursion to proceed with next level

    return TryFindParent<T>(parentObject);

  }

}

/// <summary>

/// This method is an alternative to WPF's

/// <see cref="VisualTreeHelper.GetParent"/> method, which also

/// supports content elements. Keep in mind that for content element,

/// this method falls back to the logical tree of the element!

/// </summary>

/// <param name="child">The item to be processed.</param>

/// <returns>The submitted item's parent, if available. Otherwise

/// null.</returns>

public static DependencyObject GetParentObject(this DependencyObject child)

{

  if (child == null) return null;

  //handle content elements separately

  ContentElement contentElement = child as ContentElement;

  if (contentElement != null)

  {

    DependencyObject parent = ContentOperations.GetParent(contentElement);

    if (parent != null) return parent;

    FrameworkContentElement fce = contentElement as FrameworkContentElement;

    return fce != null ? fce.Parent : null;

  }

  //also try searching for parent in framework elements (such as DockPanel, etc)

  FrameworkElement frameworkElement = child as FrameworkElement;

  if (frameworkElement != null)

  {

    DependencyObject parent = frameworkElement.Parent;

    if (parent != null) return parent;

  }

  //if it's not a ContentElement/FrameworkElement, rely on VisualTreeHelper

  return VisualTreeHelper.GetParent(child);

}

This snippet works with arbitrary dependency objects that are of Type Visual or Visual3D. So let’s say you need a reference to the Window that hosts a given Button control somewhere, all you need is this:

Button myButton = ...

Window parentWindow = UIHelper.TryFindParent<Window>(myButton);

The above TryFindParent method also makes it easy to get an item at a given position. The method below performs a hit test based on a given position. If hit testing does not return the requested item (e.g. a clicked CheckBox on a tree, while you are keen on the TreeViewItem that hosts the CheckBox), the procedure delegates the lookup to TryFindParent.

This comes in very handy for mouse-related events if you just need to now what’s under your mouse pointer:

/// <summary>

/// Tries to locate a given item within the visual tree,

/// starting with the dependency object at a given position.

/// </summary>

/// <typeparam name="T">The type of the element to be found

/// on the visual tree of the element at the given location.</typeparam>

/// <param name="reference">The main element which is used to perform

/// hit testing.</param>

/// <param name="point">The position to be evaluated on the origin.</param>

public static T TryFindFromPoint<T>(UIElement reference, Point point)

  where T:DependencyObject

{

  DependencyObject element = reference.InputHitTest(point)

                               as DependencyObject;

  if (element == null) return null;

  else if (element is T) return (T)element;

  else return TryFindParent<T>(element);

}

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Finding an ancestor of a WPF dependency object

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