WPF TreeView tools

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Introduction

While working with the WPF TreeView and data binding, I ran into the problem that the TreeViewItems and my real objects were only loosely connected. That's why I decided to code some methods for the most important tasks like selecting, expanding, ... TreeViewItems that take my bound object as a parameter.

Using the Code

To use my small library, simply copy the file into your project. All the methods are implemented as extension methods for the TreeView or the TreeViewItem class.

The heart and soul of this library is the GetItemFromObject method:

/// <summary>
/// Returns the TreeViewItem of a data bound object.
/// </summary>
/// <param name="treeView">TreeView</param>
/// <param name="obj">Data bound object</param>
/// <returns>The TreeViewItem of the data bound object or null.</returns>
public static TreeViewItem GetItemFromObject(this TreeView treeView, object obj)
{
  try
  {
    DependencyObject dObject = GetContainerFormObject(treeView, obj);
    TreeViewItem tvi = dObject as TreeViewItem;
    while (tvi == null)
    {
      dObject = VisualTreeHelper.GetParent(dObject);
      tvi = dObject as TreeViewItem;
    }
    return tvi;
  }
  catch { }
  return null;
}

private static DependencyObject 
        GetContainerFormObject(ItemsControl item, object obj)
{
  DependencyObject dObject = null;
  dObject = item.ItemContainerGenerator.ContainerFromItem(obj);
  if (dObject == null)
  {
    if (item.Items.Count > 0)
    {
      foreach (object childItem in item.Items)
      {
        ItemsControl childControl = item.ItemContainerGenerator.
              ContainerFromItem(childItem)as ItemsControl;
        dObject = GetContainerFormObject(childControl, obj);
        if (dObject != null)
        {
          break;
        }
      }
    }
  }
  return dObject;
}

By this, you get the TreeViewItem container of your object. Unfortunately, this method works only if the TreeViewNode with the object is visible (all parent nodes must be expanded). The GetContainerFromObject method is an internal helper to walk the VisualTree to find your object in the deeper tree levels. The VisualTreeHelper is the main reason why all parent nodes must be expanded.

All the following methods use this method to get the TreeViewItem, and then set or read the TreeViewItem's property.

public static void SelectObject(this TreeView treeView, object obj)
public static void SelectObject(this TreeView treeView, object obj, bool selected) 
public static bool IsObjectSelected(this TreeView treeView, object obj)
public static bool IsObjectFocused(this TreeView treeView, object obj)
public static void ExpandObject(this TreeView treeView, object obj)
public static void ExpandObject(this TreeView treeView, object obj, bool expanded)
public static bool IsObjectExpanded(this TreeView treeView, object obj)

The last method simply returns the parent TreeViewItem of a given TreeViewItem (can anyone tell me why this is missing in WPF or am I just blind!)

public static TreeViewItem GetParentItem(this TreeViewItem item)

Points of Interest

The TreeView shows me both sides of WPF: you get a super simple data binding with hierarchy, automatic updates, and so on, but on the other side, such simple things like walking a TreeView, expanding/collapsing items get a bit complex if you use data binding because of the super flexible Visual and Logical tree architecture.

I will extend this library in the future and update it from time to time. Any suggestions are welcome.

History

• 05-05-2009: Original version.