WPF ContentTemplateSelector weirdness

Question

Goal: I wish to have an object that contains my data and have it bound to a ContentPresenter that uses a custom ContentTemplateSelector to select the proper data template for rendering in the main control.

Problem: DataTemplate does not render as expected in the main control; It does not render the specified View control.

Code:

MainView.xaml:

<Window x:Class="WpfContentTemplateSelector.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:this="clr-namespace:WpfContentTemplateSelector"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.Resources>
            <this:ObjectWrapper x:Key="wrapper"/>
        </Grid.Resources>

        <ContentPresenter Content="{Binding Value}" DataContext="{StaticResource ResourceKey=wrapper}">
            <ContentPresenter.ContentTemplateSelector>
                <this:TemplateSelector/>
            </ContentPresenter.ContentTemplateSelector>
        </ContentPresenter>
    </Grid>
</Window>

DataObject.cs:

class DataObject
{
    public string Title { get; set; }

    public DataObject()
    {
        Title = "Title";
    }
}

ObjectWrapper.cs:

class ObjectWrapper
{
    public DataObject Value { get; set; }

    public ObjectWrapper()
    {
        Value = new DataObject();
    }
}

TemplateSelector.cs:

class TemplateSelector : DataTemplateSelector
{
    public override DataTemplate SelectTemplate(object item, DependencyObject container)
    {
        DataTemplate template = new DataTemplate(typeof(View));

        return template;
    }
}

View.xaml:

<UserControl x:Class="WpfContentTemplateSelector.View"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:this="clr-namespace:WpfContentTemplateSelector"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300" Background="Navy">
    <Grid Background="Navy">
        <Button Height="30" Content="{Binding Title}"/>
    </Grid>
</UserControl>

Summary:

The ObjectWrapper initializes.
The DataObject initializes.
On initialization, the TemplateSelector creates a new DataTemplate.
The created DataTemplate uses the View type in its constructor.
The objects are all initialized, the datacontext of the main view is set to the DataObject, and the view still doesn't render to the main window.

score 2 · Accepted Answer · edited Jul 23 '14 at 22:09

Your problem is that in your TemplateSelector you're defining a DataTemplate for type View but you give it no content. Your code is the equivalent of the following:

<ContentPresenter Content="{Binding Value}" DataContext="{StaticResource ResourceKey=wrapper}">
    <ContentPresenter.ContentTemplate>
        <DataTemplate DataType="this:View">
        </DataTemplate>
    </ContentPresenter.ContentTemplate>
</ContentPresenter>

Here you are merely defining an empty DataTemplate for type View, when what you actually want is a DataTemplate containing a View control:

<ContentPresenter Content="{Binding Value}" DataContext="{StaticResource ResourceKey=wrapper}">
    <ContentPresenter.ContentTemplate>
        <DataTemplate>
            <this:View />
        </DataTemplate>
    </ContentPresenter.ContentTemplate>
</ContentPresenter>

So what you need to do is modify your TemplateSelector to return a proper DataTemplate object.

Thank you very much for your response. Though I am not able to define the view in XAML, your response more clearly identified the issue for me. — Tyler Kendrick, Aug 20 '12 at 18:55
@TylerKendrick I figured you would have no problem fixing your `TemplateSelector` once you know what the problem is, and indeed I see from your own answer that you've managed :) — Adi Lester, Aug 20 '12 at 19:14

score 0 · Answer 2 · answered Aug 20 '12 at 18:58

Adi Lester's response revealed that the child nodes for the DataTemplate object I was creating didn't render the view used in the constructor.

To add to a DataTemplate's visual tree in the code-behind, I augmented my TemplateSelector object to use the following code:

class TemplateSelector : DataTemplateSelector
{
    public override DataTemplate SelectTemplate(object item, DependencyObject container)
    {
        View view = item as View;
        DataTemplate template = new DataTemplate(typeof(View));

        FrameworkElementFactory factory = new FrameworkElementFactory(typeof(View));
        template.VisualTree = factory;

        return template;
    }
}

This successfully changes the visual tree and renders the view using my custom TemplateSelector to provide a DataTemplate.

WPF ContentTemplateSelector weirdness

2 Answers2