Filtering hierarchical data and another TreeView bug

Well, well, well. Yet another TreeView bug discovered, while answering another WPF question. But, before it, let's answer it: "How to filter hierarchical data?"

What we have? We have treeview with XML data binded to it.
What we need? To filter it - for example filter out all odd nodes in any level.
How to do? Regular way, by using Predictate generic object.

Let's start. Light, motor, camera, Data

<root> <leaf id="1" name="leaf1"> <group id="1" name="group1"> <item name="item1" id="1"> <subitem id="1">test 1</subitem> <subitem id="5">test 2</subitem> <subitem id="5">test 3</subitem> <subitem id="5">test 4</subitem> <subitem id="5">test 5</subitem> </item> <item name="item2" id="2"> <subitem id="1">test 1</subitem> <subitem id="5">test 2</subitem> <subitem id="5">test 3</subitem> <subitem id="5">test 4</subitem> <subitem id="5">test 5</subitem> </item> 
      
 .....
 

Data template (hierarchical of cause)

<HierarchicalDataTemplate DataType="leaf" ItemsSource ="{Binding XPath=*}"> <TextBlock Text="{Binding XPath=@name}" /> </HierarchicalDataTemplate> <HierarchicalDataTemplate DataType="group" ItemsSource ="{Binding XPath=*}"> <TextBlock Text="{Binding XPath=@name}" Foreground="Blue" /> </HierarchicalDataTemplate> <HierarchicalDataTemplate DataType="item" ItemsSource ="{Binding XPath=*}"> <TextBlock Text="{Binding XPath=@name}" Foreground="Red"/> </HierarchicalDataTemplate> 
      
 
 

Data provider and control to host our data

<XmlDataProvider Source="XMLFile1.xml" x:Key="mydata" XPath="*"/> 

    
 
      
<TreeView Name="myTree" ItemsSource="{Binding Source={StaticResource mydata}, XPath=*}"/>  
          
 
 
 
 

Now let's add checkbox to switch filtering on and off

<CheckBox Name="predCheck" Checked="onPredChecked" Unchecked="onPredUnchecked">Filter by predicate object</CheckBox>

And now, take care on those routed events...

void onPredChecked(object sender, RoutedEventArgs e) { ICollectionView view = CollectionViewSource.GetDefaultView(myTree.ItemsSource); view.Filter = new Predicate<object>(FilterOdds); } void onPredUnchecked(object sender, RoutedEventArgs e) { ICollectionView view = CollectionViewSource.GetDefaultView(myTree.ItemsSource); view.Filter = null; } 
      
 
 

How to filter (FilterOdds method)?

bool FilterOdds(object item) { XmlElement elem = item as XmlElement; bool res = false; if (elem != null) { res = int.Parse(elem.SelectSingleNode("@id").InnerText) % 2 == 1; } return res; } 
      
 
 

Now, let's filter each node, while it's expanding.

void onExpanded(object sender, RoutedEventArgs e) { TreeViewItem item = sender as TreeViewItem; if (item != null) { ICollectionView view = CollectionViewSource.GetDefaultView(item.ItemsSource); if (view != null) { if ((bool)predCheck.IsChecked) { view.Filter = new Predicate<object>(FilterOdds); } else  { //Remove comment to stop expanding level 3  //view.Filter = null;  } } } //debug  Console.WriteLine("Item {0} on container {1}", myTree.ItemContainerGenerator.IndexFromContainer(item), ItemsControl.ItemsControlFromItemContainer(item).Name); } 
      
 
 

Cool everything should work, isn't it? Yes, except the weird bug of treeview, that preventing it from expanding 3rd level node, if filter applied. Try to compile and run it. If the check box unchecked (no filtering) we can easily expand each node on every level. See yourself

But if we'll check the checkbox, 3rd level will be inaccessible for us (as well as all deeper levels) See...

If you'll try to expand it, focus will move one level up and node remains collapsed. Pretty bad, huh... Good unbugged programming...

Source code for this article