How do i correctly use ContentTemplateSelector with ContentControl?

Question

I have lots of ContentControl objects and I need a border around a few of them, not all. I was able to get it working with the below code:

<ContentControl Margin="2" Grid.Row="0" Grid.Column="1" BorderThickness="5" BorderBrush="Beige">
    <!-- ContentControl.Template to get the border -->
    <ContentControl.Template>
        <ControlTemplate TargetType="ContentControl">
            <Border Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" >
                <ContentPresenter
                        Content="{TemplateBinding Content}"
                        ContentTemplate="{TemplateBinding ContentTemplate}"
                        Cursor="{TemplateBinding Cursor}"
                        Margin="{TemplateBinding Padding}" />
            </Border>
        </ControlTemplate>
    </ContentControl.Template>
    <StackPanel>
        <Label Content="Paid" HorizontalAlignment="Right" />
        <Label Content="{Binding ReceivedAmount}" HorizontalAlignment="Right" />
    </StackPanel>
</ContentControl>

I want to move the entire ContentTemplate section to an other resource file and merge them. I added a new resource file and moved the below part of code to it.

<ControlTemplate TargetType="ContentControl" x:Key="BalanceAmountControls">
    <Border Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" >
        <ContentPresenter
                Content="{TemplateBinding Content}"
                ContentTemplate="{TemplateBinding ContentTemplate}"
                Cursor="{TemplateBinding Cursor}"
                Margin="{TemplateBinding Padding}" />
    </Border>
</ControlTemplate>

When I try to change the actual ContentControl code to this, I get an error saying

"An object of type System.Windows.Controls.ControlTemplate cannot be applied to a property that expects the type System.Windows.Controls.DataTemplateSelector"

<!-- Balance amount -->
<ContentControl Margin="2" Grid.Row="0" Grid.Column="2" BorderThickness="5" BorderBrush="Beige" ContentTemplateSelector="{StaticResource BalanceAmountControls}">
    <!-- ContentControl.Template to get the border -->
    <StackPanel>
        <Label Content="Balance" HorizontalAlignment="Right" />
        <Label Content="{Binding BalanceAmount}" HorizontalAlignment="Right" />
    </StackPanel>
</ContentControl>

How do I resolve this error?

Answer 1

An object of type ControlTemplate cannot be applied to a property that expects the type DataTemplateSelector

This error message is very explicit. You are assigning a ControlTemplate to a ContentControl.DataTemplateSelector . Type mismatch. You are assigning

<ControlTemplate TargetType="ContentControl" x:Key="BalanceAmountControls">

to

<ContentControl ContentTemplateSelector="{StaticResource BalanceAmountControls}"> .

Solution:
You need to implement your own DataTemplateSelector :

public class ContentControlDataTemplateSelector : DataTemplateSelector
{
    public override DataTemplate
        SelectTemplate(object item, DependencyObject container)
    {
        FrameworkElement element = container as FrameworkElement;

        if (element != null && item != null && item is Task)
        {
            if (// your condition)
                return
                    element.FindResource("BalanceAmountControls") as  DataTemplate;
            else
                return
                    element.FindResource("NonBalanceAmountControls") as DataTemplate;
        }

        return null;
    }
}

Apply the template selector:

<ContentControl ContentTemplateSelector="{StaticResource ContentControlDataTemplateSelector}" />

Now you need to create the proper DataTemplate resources which describe the individual visual appearance of the data that you have to bind to the ContentControl.Content property.