WPF DataTemplateSelector.SelectTemplate not called for a ContentControl-derived type

Question

I'm trying to build a ContentControl-derived control (let's call it MyContentControl) that will have its ControlTemplate set by an instance of a DataTemplateSelector-derived type (let's call it MyTemplateSelector).

When I try to this:

ContentControl contentControl = new ContentControl();
contentControl.ContentTemplateSelector = new MyTemplateSelector();
contentControl.Content = "Some ContentControl Content";

MyContentControl myContentControl = new MyContentControl();    
myContentControl.ContentTemplateSelector = new MyTemplateSelector();
myContentControl.Content = "Some MyControl Content";

I expect that, when I set content on those controls, MyTemplateSelector's override of DataTemplateSelector.SelectTemplate() method gets called for both contentControl and myContentControl.

In reality, it gets called only for contentControl. What do I need to do (and why!) to make it work for myContentControl too?

(Not sure if it's relevant, but for the moment MyContentControl does not do anything with DependencyProperties other than overriding metadata information for DefaultStyleKeyProperty.)

Answer 1

You might need to post more of your code, because I just created a simple example and it worked fine. My DataTemplate only contains a TextBox, my DataTemplateSelector always returns that DataTemplate, and both a ContentControl and a class derived from ContentControl use my DataTemplateSelector. In both cases a TextBox was displayed.

Answer 2

OK, here is a bit more elaborated example:

1) Create MyContentControl:

public class MyContentControl : ContentControl
{
  static MyContentControl()
  {
    DefaultStyleKeyProperty.OverrideMetadata(typeof (MyContentControl),
                                             new FrameworkPropertyMetadata(typeof (MyContentControl)));
  }
  public MyContentControl() {}
}

2) Create MyTemplateSelector:

public class MyTemplateSelector : DataTemplateSelector
{
  public override DataTemplate SelectTemplate(object item, DependencyObject container)
  {
    return null;  // <== Place the breakpoint here
  }
}

3) Add ContentControl and MyContent control to your main window (for example):

<StackPanel>
    <local:MyContentControl x:Name="myContentControl" />
    <ContentControl x:Name="contentControl" />
</StackPanel>

4) Add this code somewhere after InitializeComponent (or in Loaded handler):

myContentControl.ContentTemplateSelector = new MyTemplateSelector();
myContentControl.Content = "123";

contentControl.ContentTemplateSelector = new MyTemplateSelector();
contentControl.Content = "ABC";

The breakpoint mentioned in step (2) gets hit only once, for content="ABC" and contentControl element.

Answer 3

I got the same problem before, and I solve it with this (http://stackoverflow.com/questions/1314560/notify-datatemplateselector-about-the-change) hint.

My problem was, I want a ContentPresenter which changes embedded UserControl when the ComboBox selection changed.

The Combobox+ContentPresenter XAML is

        <ComboBox Name="comboBoxControl" Grid.Row="1" Grid.Column="1" SelectionChanged="comboBox_SelectionChanged">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="SelectionChanged">
                <cmd:EventToCommand Command="{Binding Path=ChangeControlCommand, Mode=OneWay}" CommandParameter="{Binding Path=SelectedItem.Content, ElementName=comboBoxControlType}" />
            </i:EventTrigger>
        </i:Interaction.Triggers>
        <ComboBoxItem>UserControl-1-</ComboBoxItem>
        <ComboBoxItem>UserControl-2-</ComboBoxItem>
    </ComboBox>
<ContentPresenter Name="contentPresenter" ContentTemplateSelector="{Binding Source={StaticResource controlCueTemplateSelector}}" 
                      Content="{Binding}" />

As you can see, the command binding with MVVM manner was my approach. Although you might not want to write a code-behind, kindly write a code-behind with appropriate event as below.

    private void comboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        var content = contentPresenter.Content;
        contentPresenter.ClearValue(ContentPresenter.ContentProperty);
        contentPresenter.SetValue(ContentPresenter.ContentProperty, content);
    }

Bottomline is, you need to reset the binded target object (in my case, the Content property).