# Other .NET Programming > Windows Presentation Foundation (WPF) & XAML forum >  Trying To Bind ToolTipOpening Event Handler to A TreeView Item

## crokett

I'm trying to bind a tooltipOpening Event handler to a TreeView Item in XAML.  However, the g.i.cs file that gets generated instead binds the Event Handler to a button and when the window is initialized I get an invalid cast exception.   Visual Studio is binding the tool tip to a label that follows the treeview definition and not to the treeview item.

this is the XAML code



```

 <StackPanel Grid.Column="1">
                <Label x:Name="ISLLabel" Content="ISLs" Margin="0,0,45,0" FontWeight="Bold" Height="67"/>
                <TreeView x:Name="ISLTreeView" Height="auto" Background="GhostWhite" 
                           BorderThickness="0" Width="auto"
                           ItemsSource="{Binding}" 
                            ScrollViewer.VerticalScrollBarVisibility="auto">

                    <TreeView.ItemContainerStyle>
                     
                        <Style TargetType="{x:Type TreeViewItem}">
                            <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
                            <Setter Property="ToolTip">
                                <Setter.Value>
                                    <ToolTip ToolTipOpening="ISL_TreeViewTipOpening"></ToolTip>
                                </Setter.Value>
                            </Setter>
                            <Style.Triggers>
                                <Trigger Property="IsSelected" Value="True">
                                    <Setter Property="FontWeight" Value="Bold" />
                                </Trigger>
                              
                            </Style.Triggers>
                        </Style>
                    </TreeView.ItemContainerStyle>

                </TreeView>

                <Label x:Name="NeighborLabel" Content="Neighbors List"></Label>
                <TreeView x:Name="NeighborsTreeView" Height="Auto" 
                          Background="GhostWhite" BorderThickness="0" Width="auto" 
                          ItemsSource="{Binding}"
                          ScrollViewer.VerticalScrollBarVisibility="auto">
            
                </TreeView>
```


this is from the auto-generated g.i.cs file for the window



```
       #line 104 "..\..\..\SwitchBrowser.xaml"
            this.NeighborLabel.ToolTipOpening += new System.Windows.Controls.ToolTipEventHandler(this.ISL_TreeViewTipOpening);
```

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