I have a hypothetical tree view that contains this data:


I am trying to filter the nodes in order to show only the nodes that contain a certain text. Say if I specify "L", the tree will be filtered and show only RootNode->Leaf and SecondRoot->flowers (because they both contain the letter L).

Following the m-v-vm pattern, I have a basic TreeViewViewModel class like this:

public class ToolboxViewModel
    readonly ObservableCollection<TreeViewItemViewModel> _treeViewItems = new ObservableCollection<TreeViewItemViewModel>();
    public ObservableCollection<TreeViewItemViewModel> Headers
        get { return _treeViewItems; }

    private string _filterText;
    public string FilterText
        get { return _filterText; }
            if (value == _filterText)

            _filterText = value;

            ICollectionView view = CollectionViewSource.GetDefaultView(Headers);
            view.Filter = obj => ((TreeViewItemViewModel)obj).ShowNode(_filterText);

And a basic TreeViewItemViewModel:

public class ToolboxItemViewModel
    public string Name { get; private set; }
    public ObservableCollection<TreeViewItemViewModel> Children { get; private set; }
    public bool ShowNode(string filterText)
        ... return true if filterText is contained in Name or has children that contain filterText ... 

Everything is setup in the xaml so I see the treeview and search box.

When this code is exercised, the filter only applies to the Root nodes which is insufficient. Is there a way to make the filter trickle down in the hierarchy of nodes so that my predicate is called for every node ? In other words, can the filter be applied to the TreeView as a whole ?

  • 2
    What did you end up doing? Any performance info you can relay or other solution? – Aaron McIver Dec 31 '10 at 21:52

Unfortunately there is no way to make same Filter apply to all nodes automatically. Filter is a property (not a DP) of ItemsCollection which is not DependencyObject and so DP Value inheritance isn't there.

Each node in the tree has its own ItemsCollection which has its own Filter. The only way to make it work is to manually set them all to call the same delegate.

Simplest way would be to expose Filter property of type Predicate<object> at your ToolBoxViewModel and in its setter fire an event. Then ToolboxItemViewModel will be responsible for consuming this event and updating its Filter.

Aint pretty and I'm not sure what the performance would be like for large amounts of items in the tree.


This is how I filtered the items on my TreeView:

I have the class:

class Node
    public string Name { get; set; }
    public List<Node> Children { get; set; }

    // this is the magic method!
    public Node Search(Func<Node, bool> predicate)
         // if node is a leaf
         if(this.Children == null || this.Children.Count == 0)
             if (predicate(this))
                return this;
                return null;
         else // Otherwise if node is not a leaf
             var results = Children
                               .Select(i => i.Search(predicate))
                               .Where(i => i != null).ToList();

             if (results.Any()){
                var result = (Node)MemberwiseClone();
                result.Items = results;
                return result;
             return null;

Then I could filter results as:

// initialize Node root
// pretend root has some children and those children have more children
// then filter the results as:
var newRootNode = root.Search(x=>x.Name == "Foo");

The only way I've found to do this (which is a bit of a hack), is to create a ValueConverter that converts from IList to IEnumerable. in ConvertTo(), return a new CollectionViewSource from the passed in IList.

If there's a better way to do it, I'd love to hear it. This seems to work, though.


I decided to use the treeview by Philipp Sumi mentioned here : http://www.codeproject.com/KB/WPF/versatile_treeview.aspx

And applied a filter to it as shown here : http://www.hardcodet.net/2008/02/programmatically-filtering-the-wpf-treeview

I couldn't recommend it enough :)


You can get the TreeViewItem for a given element in a tree using ItemContainerGenerator and once you have that you are in a position to set the Filter.

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