Silverlight Control Template Doesn’t Get Applied : Silverlight Feeds

Silverlight Control Template Doesn’t Get Applied

by via Jeff Handley on 10/30/2008 1:15:02 AM

This is something that has bitten me several times, so I thought I’d write it down. Maybe I’ll remember, and maybe I’ll help others when they hit this too.

The scenario happens when you want to create a new control that can have a template applied to it. Let’s start with this control definition:

        1: using System;

       2: using System.Windows.Controls;

       3: using System.Windows.Markup;

       4:  

       5: namespace ControlTemplate

       6: {

       7:     [ContentProperty("Content")]

       8:     public class MyTemplatedControl : ContentControl

       9:     {

      10:  

      11:     }

      12: }

Then you create your generic.xaml file under the themes folder, and you add a template for your control.

       1: <ResourceDictionary

       2:     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

       3:     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

       4:     xmlns:local="clr-namespace:ControlTemplate">

       5:     

       6:     <Style TargetType="local:MyTemplatedControl">

       7:         <Setter Property="Template">

       8:             <Setter.Value>

       9:                 <ControlTemplate TargetType="local:MyTemplatedControl">

      10:                     <TextBlock Text="This is my custom control template" />

      11:                 </ControlTemplate>

      12:             </Setter.Value>

      13:         </Setter>

      14:     </Style>

      15: </ResourceDictionary>

Then you put your custom control on a page.

       1: <UserControl x:Class="ControlTemplate.Page"

       2:              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 

       3:              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 

       4:              xmlns:local="clr-namespace:ControlTemplate">

       5:     <Grid x:Name="LayoutRoot" Background="White">

       6:         <local:MyTemplatedControl />

       7:     </Grid>

       8: </UserControl>

When you run the app, you expect to see “This is my custom control template” inside the page, but you don’t. You get a plain white page. You start trying all kinds of things, trying to figure out why your textblock isn’t showing up. Eventually you beat your head against the desk a few times and then ask someone to come look to see what you’re doing wrong.

“You need to set the DefaultStyleKey property on your control.”

“Ahh… I forgot again!” You add 3 lines of code to your control, run, and poof… it works! Here’s what your control looks like now:

       1: using System;

       2: using System.Windows.Controls;

       3: using System.Windows.Markup;

       4:  

       5: namespace ControlTemplate

       6: {

       7:     [ContentProperty("Content")]

       8:     public class MyTemplatedControl : ContentControl

       9:     {

      10:         public MyTemplatedControl()

      11:         {

      12:             this.DefaultStyleKey = typeof(MyTemplatedControl);

      13:         }

      14:     }

      15: }

Without setting the DefaultStyleKey property to the control’s own type, the template doesn’t get applied. Set that property in your constructor and you’re good to go.