Modifying a DataTemplate TreeView at Run Time

Question

I have TreeView3 levels in my WPF application.

Level 1 and level 2 have their own HierarchicalDataTemplate. Level 3 has its own DataTemplate.

Here is the XAML code:

<Window.Resources>
    <HierarchicalDataTemplate x:Key="Level1Template" 
                          ItemsSource="{Binding Value}"
                          ItemTemplate="{StaticResource Level2RedTemplate}">
        <Border Background="Green">
            <TextBlock Text="Level1"/>
        </Border>
    </HierarchicalDataTemplate>

    <HierarchicalDataTemplate x:Key="Level2RedTemplate"
                          ItemsSource="{Binding Value}"
                          ItemTemplate="{StaticResource Level3Template}">
        <Border Background="Red">
            <TextBlock Text="Level2"/>
        </Border>
    </HierarchicalDataTemplate>

    <HierarchicalDataTemplate x:Key="Level2YellowTemplate"
                          ItemsSource="{Binding Value}"
                          ItemTemplate="{StaticResource Level3Template}">
        <Border Background="Yellow">
            <TextBlock Text="Level2"/>
    </HierarchicalDataTemplate>

    <DataTemplate x:Key="Level3Template">
        <Border Background="LightBlue">
            <TextBlock Text="Level3"/>
        </Border>
    </DataTemplate>

</Window.Resources>

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>

    <Button Grid.Row="0"
            Content="Change Template"
            Click="ChangeTemplate" />

    <TreeView Grid.Row="1"
              Name="tv"
              ItemsSource="{Binding Items}"
              ItemTemplate="{StaticResource Level1Template}"/>
</Grid>

It works fine so far. The problem starts when I want to change DataTemplateLevel2 elements by clicking a button in my window (see image below).

I tried to assign a new one HierarchicalDataTemplatefor mine TreeViewfrom the code behind (in the button event handler) as follows:

Private Sub ChangeTemplate()

    CType(tv.ItemTemplate, HierarchicalDataTemplate).ItemTemplate = CType(Me.FindResource("Level2YellowTemplate"), HierarchicalDataTemplate)

End Sub

This is not possible because I get the error message: "as soon as the template object is used (sealed), it cannot be changed."

Is there any way to change this template?

Answer 1

@Bob, :

UserControl, TreeView.

HierarchicalDataTemplate 1 :

<HierarchicalDataTemplate x:Key="Level1Template" 
                      ItemsSource="{Binding Value}"
                      ItemTemplateSelector="{StaticResource MySelector}">
    <Border Background="Green">
        <TextBlock Text="Level1"/>
    </Border>
</HierarchicalDataTemplate>

MySelector Public Overrides Function SelectTemplate(item As Object, container As DependencyObject) As DataTemplate. container, UserControl .

ItemsSource ItemsSource, usercontrol. TemplateSelector, .