Create Event Handler for TreeViewItem in WPF - wpf

Question

Im adding items to TreeView control via ItemsSource property and ItemTemplate property to set the template for TreeViewItem. How can i add an event handler to handle selection change event on TreeViewItems?
For now my ItemTemplate looks like this:
<Window.Resources><DataTemplate x:Key="PeerDetailTemplate">
<TextBlock Text="{Binding DESCRIPTION}" Tag="{Binding ID}" GotFocus="GetModules"/>
</DataTemplate></Window.Resources>
But it doesnt work (GetModules is not called). Im new to WPF, so show me the right direction to do such things, please.

Answer 1

If you want to capture the SelectedItemChanged event in a TreeView, then you need to set the event handler on the parent node, i.e.,
XAML
<StackPanel>
<TreeView SelectedItemChanged="OnTreeViewSelectedItemChanged">
<TreeViewItem Header="Desktop">
<TreeViewItem Header="Computer" />
<TreeViewItem Header="My Documents" />
<TreeViewItem Header="c:\" />
</TreeViewItem>
<TreeViewItem Header="Recyle Bin" >
<TreeViewItem Header="foo.txt" />
<TreeViewItem Header="bar.txt" />
<TreeViewItem Header="fizz.buzz" />
</TreeViewItem>
<TreeViewItem Header="Control Panel" >
<TreeViewItem Header="Programs" />
<TreeViewItem Header="Security" />
<TreeViewItem Header="User Accounts" />
</TreeViewItem>
</TreeView>
<TextBlock Margin="20" x:Name="MyTextBlock" />
</StackPanel>
Code Behind:
private void OnTreeViewSelectedItemChanged( object sender, RoutedPropertyChangedEventArgs<object> e )
{
MyTextBlock.Text = ( (TreeViewItem) ( (TreeView) sender ).SelectedItem ).Header.ToString();
}

Answer 2

You'll need to add an event handler to the TreeView's SelectedItemChanged event.
<TreeView x:Name="myTreeView"
SelectedItemChanged="myTreeView_SelectedItemChanged"
ItemTemplate="{StaticResource PeerDetailTemplate} />
Since this is fired after the selection is changed, you can use the TreeView's selected item property to access the tree view item:
private void myTreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
TreeViewItem selectedItem = (TreeViewItem)myTreeView.SelectedItem;
// do stuff
}

Answer 3

Selection and Selection and focus are two different concepts. It sounds like you're interested in selection, which in this case is a property of the TreeView. Event TreeView.SelectedItemChanged will notify you of selection changes and property TreeView.SelectedItem will tell you what is selected.

Answer 4

There are different ways to Bind of the SelectedItemChanged event of TreeviewItem:
Method 1: Direct Attaching Event
The attachment of the event can be done in Xaml
<TreeView x:Name="treeview1" HorizontalAlignment="Left" Height="243" Margin="30,211,0,0" VerticalAlignment="Top" Width="667" SelectedItemChanged="TreeView_SelectedItemChanged">
<TreeViewItem Header="TreeViewItem"/>
</TreeView>
Private void TreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
}
Or on code Behind
myTreeview.SelectedItemChanged += new RoutedPropertyChangedEventHandler<object>(TreeView_SelectedItemChanged);
private void TreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
}
Method 2 Usage of Extended Class
public class ExtendedTreeView : TreeView
{
public ExtendedTreeView()
: base()
{
this.SelectedItemChanged += new RoutedPropertyChangedEventHandler<object>(TreeView_SelectedItemChanged);
}
void TreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (SelectedItem != null)
{
SetValue(SelectedItem_Property, SelectedItem);
}
}
public object SelectedItem_
{
get { return (object)GetValue(SelectedItem_Property); }
set { SetValue(SelectedItem_Property, value); }
}
public static readonly DependencyProperty SelectedItem_Property = DependencyProperty.Register("SelectedItem_", typeof(object), typeof(ExtendedTreeView), new UIPropertyMetadata(null));
}
Next just create the Treeview with the new custom class object.
ExtendedTreeView myTreeview = new ExtendedTreeView();
Method 3 Usage of Behavior
public class BindableSelectedItemBehavior : Behavior<TreeView>
{
#region SelectedItem Property
public object SelectedItem
{
get { return (object)GetValue(SelectedItemProperty); }
set { SetValue(SelectedItemProperty, value); }
}
public static readonly DependencyProperty SelectedItemProperty =
DependencyProperty.Register("SelectedItem", typeof(object), typeof(BindableSelectedItemBehavior), new UIPropertyMetadata(null, OnSelectedItemChanged));
private static void OnSelectedItemChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
var item = e.NewValue as TreeViewItem;
if (item != null)
{
item.SetValue(TreeViewItem.IsSelectedProperty, true);
}
}
#endregion
protected override void OnAttached()
{
base.OnAttached();
this.AssociatedObject.SelectedItemChanged += OnTreeViewSelectedItemChanged;
}
protected override void OnDetaching()
{
base.OnDetaching();
if (this.AssociatedObject != null)
{
this.AssociatedObject.SelectedItemChanged -= OnTreeViewSelectedItemChanged;
}
}
Next just attach the Treeview to the Behavior
On Xaml file
<TreeView>
<e:Interaction.Behaviors>
<behaviours:BindableSelectedItemBehavior SelectedItem="{Binding SelectedItem, Mode=TwoWay}" />
</e:Interaction.Behaviors>
</TreeView>
Or on Code Behind
BindableSelectedItemBehavior selectedItemBehavior = new BindableSelectedItemBehavior();
System.Windows.Interactivity.Interaction.GetBehaviors(treeview1).Add(selectedItemBehavior);
Cordially