Dynamic template for a ComboBox in ListBox - wpf

Question

I have a ListBox with an embedded ComboBox:
<ListBox ItemsSource="{Binding}">
<ListBox.ItemTemplate>
<DataTemplate>
<ComboBox Width="100" IsEditable="False" Height="20">
<TextBlock Text="Opt#1"></TextBlock>
<TextBlock Text="Opt#2"></TextBlock>
<TextBlock Text="Opt#3"></TextBlock>
</ComboBox>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I'd like to present the ComboBox as a simple text (e.g. TextBlock) when a ListBox row is not selected, and show it as a ComboBox when the ListBox row is selected.
I was thinking that replacing ComboBox template dynamically would do the trick. How to accomplish that?
Thanks,
Leszek

Answer 1

The best way to swap templates is to use the ItemTemplateSelector propery of the ListBox and set it to a class you create which inherits from DataTemplateSelector.
Here is a link that provides an example: http://msdn.microsoft.com/en-us/library/system.windows.controls.datatemplateselector.aspx

Answer 2

I would simply use a style that replace the ListBox.ItemTemplate whenever the ListBoxItem becomes selected.
Here's a quick example
<ListBox.Resources>
<DataTemplate x:Key="TextBoxTemplate">
<TextBlock Text="{Binding }" />
</DataTemplate>
<DataTemplate x:Key="ComboBoxTemplate">
<ComboBox SelectedItem="{Binding }">
<ComboBoxItem>Opt#1</ComboBoxItem>
<ComboBoxItem>Opt#2</ComboBoxItem>
<ComboBoxItem>Opt#3</ComboBoxItem>
</ComboBox>
</DataTemplate>
<Style TargetType="{x:Type ListBoxItem}">
<Setter Property="Template" Value="{StaticResource TextBoxTemplate}" />
<Style.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter Property="Template" Value="{StaticResource ComboBoxTemplate}" />
</Trigger>
</Style.Triggers>
</Style>
</ListBox.Resources>
I'd actually suggest using IsKeyboardFocusWithin instead of IsSelected as the trigger property, because templates can let you interact with them without setting the item as selected.

Answer 3

Thanks Josh and Rachel for pointing me in a right direction.
I came up with a solution similar to the one suggested by Rachel. My problem was I could not make ItemTemplateSelector work and I did not know how to pass the state IsSelected from my listbox. I also could not use DataTemplate because my ListBox item is much more complex than a single element (I simplified it in my previous post for the sake of example).
Anyway, I came up with the following solution. It's not very elegant but it works:
I defined a new style in Application resources:
<Style x:Key="TextBlockTemplate" TargetType="ComboBox">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<TextBlock Text="{Binding}" Margin="3" />
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
I attached SelectionChanged and PreviewMouseDown handlers to my ListBox:
I defined MyListBox_PreviewMouseDown:
private void MyListBox_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
// Grab the selected list box item.
object element = (e.OriginalSource as FrameworkElement).DataContext;
var item = MyListBox.ItemContainerGenerator.ContainerFromItem(element)
as ListBoxItem;
// Mark the row in the ListBox as selected.
if (item != null)
item.IsSelected = true;
}
I defined MyListBox_SelectionChanged:
private ComboBox prevComboBox = null;
private void MyListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
// Grab the list box.
ListBox list = sender as ListBox;
// Although there could be only one item selected,
// we iterate over all selected items.
foreach (MyDataItem dat in list.SelectedItems)
{
var item = list.ItemContainerGenerator.ContainerFromItem(dat) as ListBoxItem;
// FindElement is a helper method to find an element in a visual tree.
ComboBox cbo = FindElement(item, "MyComboBox") as ComboBox;
if (cbo != prevComboBox)
{
cbo.Style = null;
if (prevComboBox != null)
prevComboBox.Style =
(Style)Application.Current.Resources["TextBlockTemplate"];
prevComboBox = cbo;
}
}
}
Thanks,
Leszek