Databinding and Triggers compatability in WPF

Question

Hi all,

I have a problem. I made a template for a TreeView and I need to set the initial value of the ToggleButton's IsChecked property depending on my model. But it turns out that setting this property using triggers/setters disables the databinding.

Is it so? If yes, give me a suggestion how it can be fixed?

<DataTemplate x:Key="CellTemplate_Name">
   <DockPanel x:Name="dock">
      <ToggleButton x:Name="Expander"
        IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"> <--- Binding
    ...
      <ToggleButton/>
    ...
   <DataTemplate.Triggers>
      <DataTrigger Binding="{Binding Path=ObjIsOpened, Converter={StaticResource DebugConverter}}" Value="true"> <--- Trigger
         <Setter TargetName="Expander" Property="IsChecked" Value="true"></Setter>
      </DataTrigger>
                    ...
   </DataTemplate.Triggers>
</DataTemplate>

Regards, Lerax.

Answer 1

Hi Lerax,

I suspect they do not disable data binding, they just have higher priority. Instead of using binding and trigger at the same time, why don't you use one of them (either binding or trigger)? E.g. you could bind to model directly, and don't use trigger at all...

Answer 2

First of all I suggest you read the excellent article by Josh Smith Simplifying the WPF TreeView by Using the ViewModel Pattern

Based on that article, I would suggest defining a style for the TreeViewItem (using the ItemContainerStyle property of the TreeView) which binds its IsExpanded property to your model object's ObjIsOpened property. Then get rid of your trigger.

Example:

<Style TargetType="TreeViewItem">
    <Setter Property="IsExpanded" 
        Value="{Binding ObjIsOpened, Converter={StaticResource DebugConverter}}"/>
</Style>

<DataTemplate x:Key="CellTemplate_Name">
   <DockPanel x:Name="dock">
      <ToggleButton x:Name="Expander"
        IsChecked="{Binding Path=IsExpanded, 
                       RelativeSource={RelativeSource 
                           AncestorType={x:Type TreeViewItem}}}"> <--- Binding
    ...
      <ToggleButton/>
    ...
</DataTemplate>