How should I set a ComboBox ControlTemplate's property based on its TemplatedParent's ItemSource's property?

Question

My ComboBox has a DataTemplate. I refer to this Can I use a different Template for the selected item in a WPF ComboBox than for the items in the dropdown part? because my request is similar to it:

<ComboBox x:Name="MyComboBox" ItemsSource="{Binding Items}"
                    Style="{StaticResource ComboBoxStyle}"
                    Template="{StaticResource ComboBoxControlTemplate}"
                    ItemTemplateSelector="{UI:ComboBoxTemplateSelector
                    SelectedItemTemplate={StaticResource ComboBoxSelectedItemDataTemplate},
                    DropdownItemsTemplate={StaticResource ComboBoxDataTemplate}}"/>

It works well but I got another request: To set the ComboBox's ToggleButton's Background based on SelectedItem. So I right click this ComboBox in the designer page, choose

Edit Template -> Edit a Copy

to generate an automatic template. In the automatically generated template I get:

<ControlTemplate x:Key="ComboBoxControlTemplate" TargetType="{x:Type ComboBox}">
  <ToggleButton>
    <Border x:Name="splitBorder" Background="{TemplateBinding Background}" ...>
      <Path x:Name="Arrow" .../>
    </Border>
  </ToggleButton>
</ControlTemplate>

So what I want to change in the above code is Background="{TemplateBinding Background}". I want the Background to be based on an ItemSource ViewModel property called SelectedName just like in DataTemplate I have something like:

<DataTemplate x:Key="ComboBoxSelectedItemDataTemplate">
    <Grid>
        ...
        <TextBlock Background="{Binding Converter="{StaticResource StringToColorConverter}", Path="SelectedName"}"/>
    </Grid>
</DataTemplate>

I searched quite a few but not sure what I should do to achieve this. Please help. Thanks.

score 0 · Accepted Answer · answered Nov 02 '20 at 15:12

Set the Background property of the ComboBox similar to how you set the Background of the TextBlock:

<ComboBox x:Name="MyComboBox" ...
          Background="{Binding SelectedItem.SelectedName, 
            RelativeSource={RelativeSource Self}, Converter={StaticResource StringToColorConverter}}">

The above binds the Background property to the SelectedName property of the currently selected item of the ComboBox.

How should I set a ComboBox ControlTemplate's property based on its TemplatedParent's ItemSource's property?

1 Answers1