Archive for June, 2009

Finding Elements in the WPF Tree – Both Ways

June 25th, 2009

A while ago I posted a helper method to traverse a (visual or logical) tree in order to find an element’s parent of a given type. The corresponding blog entry is here.

This time, I needed to search the other way: I wanted to find all descendants (direct or indirect childs) of a given element that match a given type. As a result, I came up with a complementary extension method that does the job for me:

//get all TextBox controls within the grid:
Grid container;
IEnumerable<TextBox> editors = container.FindChildren<TextBox>();


Usage Sample

As a sample, let’s use a window dialog which contains several images:

  • Images that were pasted into a RichTextBox control.
  • Images that are part of the UI, nested within the control hierarchy of a ribbon.



In order to find all these Image elements you can see on the screenshot, this will do:

//start a the root (the window itself)
Window window = this;
foreach (Image img in window.FindChildren<Image>())
  Console.WriteLine("Image source: " + img.Source);



…the above snippet produces the following output:

Image source: pack://payload:,,wpf1,/Xaml/Image1.png

Image source: pack://payload:,,wpf1,/Xaml/Image2.png

Image source: pack://application:,,,/Shared/Images/Ribbon/Paste_32x32.png

Image source: System.Windows.Media.Imaging.FormatConvertedBitmap

Image source: System.Windows.Media.Imaging.FormatConvertedBitmap

Image source: pack://application:,,,/Shared/Images/Ribbon/EditUndo.png

Image source: pack://application:,,,/Shared/Images/Ribbon/EditRedo.png

Image source: pack://application:,,,/Shared/Images/Ribbon/Bold.png

Image source: System.Windows.Media.Imaging.BitmapFrameEncode



Accordingly, in order to analyze only the contents of the rich text editor, just start on a lower level of the tree:

//only examine the contents of the editor
RichTextBox editor = this.txtContent;
foreach (Image img in editor.FindChildren<Image>())
  Console.WriteLine("Image source: " + img.Source);



(Download link at the end of the posting)

/// <summary> /// Analyzes both visual and logical tree in order to find all elements /// of a given type that are descendants of the <paramref name="source"/> /// item. /// </summary> /// <typeparam name="T">The type of the queried items.</typeparam> /// <param name="source">The root element that marks the source of the /// search. If the source is already of the requested type, it will not /// be included in the result.</param> /// <returns>All descendants of <paramref name="source"/> that match the /// requested type.</returns> public static IEnumerable<T> FindChildren<T>(this DependencyObject source) where T : DependencyObject { if (source != null) { var childs = GetChildObjects(source); foreach (DependencyObject child in childs) { //analyze if children match the requested type if (child != null && child is T) { yield return (T) child; } //recurse tree foreach (T descendant in FindChildren<T>(child)) { yield return descendant; } } } } /// <summary> /// This method is an alternative to WPF's /// <see cref="VisualTreeHelper.GetChild"/> method, which also /// supports content elements. Do note, that for content elements, /// this method falls back to the logical tree of the element. /// </summary> /// <param name="parent">The item to be processed.</param> /// <returns>The submitted item's child elements, if available.</returns> public static IEnumerable<DependencyObject> GetChildObjects( this DependencyObject parent) { if (parent == null) yield break;

if (parent is ContentElement || parent is FrameworkElement) { //use the logical tree for content / framework elements foreach (object obj in LogicalTreeHelper.GetChildren(parent)) { var depObj = obj as DependencyObject; if (depObj != null) yield return (DependencyObject) obj; } } else { //use the visual tree per default int count = VisualTreeHelper.GetChildrenCount(parent); for (int i = 0; i < count; i++) { yield return VisualTreeHelper.GetChild(parent, i); } } }


For your convenience, I’ve put together a simple helper class that contains the helper methods to search for both children and parent elements in the tree:


Happy coding 🙂

Author: Categories: WPF Tags: