Can I specify a generic type in XAML?

Question

In XAML I can declare a DataTemplate so that the template is used whenever a specific type is displayed. For example, this DataTemplate will use a TextBlock to display the name of a customer:

<DataTemplate DataType="{x:Type my:Customer}">
    <TextBlock Text="{Binding Name}" />
</DataTemplate>

I'm wondering if it's possible to define a DataTemplate that will be used any time an IList<Customer> is displayed. So if a ContentControl's Content is, say, an ObservableCollection<Customer> it would use that template.

Is it possible to declare a generic type like IList in XAML using the {x:Type} Markup Extension?

Answer 1

Not out of the box, no; but there are enterprising developers out there who have done so.

Mike Hillberg at Microsoft played with it in this post, for example. Google has others of course.

Answer 2

Not directly in xaml, however you could reference a DataTemplateSelector from xaml to choose the correct template.

public class CustomerTemplateSelector : DataTemplateSelector
{
    public override DataTemplate SelectTemplate(object item, DependencyObject container)
    {
        DataTemplate template = null;
        if (item != null)
        {
            FrameworkElement element = container as FrameworkElement;
            if (element != null)
            {
                string templateName = item is ObservableCollection<MyCustomer> ?
                    "MyCustomerTemplate" : "YourCustomerTemplate";

                template = element.FindResource(templateName) as DataTemplate;
            } 
        }
        return template;
    }
}

public class MyCustomer
{
    public string CustomerName { get; set; }
}

public class YourCustomer
{
    public string CustomerName { get; set; }
}

<ResourceDictionary 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1"
    >
    <DataTemplate x:Key="MyCustomerTemplate">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="150"/>
            </Grid.RowDefinitions>
            <TextBlock Text="My Customer Template"/>
            <ListBox ItemsSource="{Binding}" DisplayMemberPath="CustomerName" Grid.Row="1"/>
        </Grid>
    </DataTemplate>

    <DataTemplate x:Key="YourCustomerTemplate">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="150"/>
            </Grid.RowDefinitions>
            <TextBlock Text="Your Customer Template"/>
            <ListBox ItemsSource="{Binding}" DisplayMemberPath="CustomerName" Grid.Row="1"/>
        </Grid>
    </DataTemplate>
</ResourceDictionary>

<Window 
    x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" 
    Height="300" 
    Width="300"
    xmlns:local="clr-namespace:WpfApplication1"
    >
    <Grid>
        <Grid.Resources>
            <local:CustomerTemplateSelector x:Key="templateSelector"/>
        </Grid.Resources>
        <ContentControl 
            Content="{Binding}" 
            ContentTemplateSelector="{StaticResource templateSelector}" 
            />
    </Grid>
</Window>

public partial class Window1
{
    public Window1()
    {
        InitializeComponent();
        ObservableCollection<MyCustomer> myCustomers = new ObservableCollection<MyCustomer>()
        {
            new MyCustomer(){CustomerName="Paul"},
            new MyCustomer(){CustomerName="John"},
            new MyCustomer(){CustomerName="Mary"}
        };

        ObservableCollection<YourCustomer> yourCustomers = new ObservableCollection<YourCustomer>()
        {
            new YourCustomer(){CustomerName="Peter"},
            new YourCustomer(){CustomerName="Chris"},
            new YourCustomer(){CustomerName="Jan"}
        };
        //DataContext = myCustomers;
        DataContext = yourCustomers;
    }
}

Answer 3

aelij (the project coordinator for the WPF Contrib project) has another way to do it.

What's even cooler (even though it is sometime off in the future) ... is that XAML 2009 (XAML 2006 is the current version) is going to support this natively. Check out this PDC 2008 session for info on it and more.

Answer 4

You also can wrap your generic class in a derived class that specifies the T

public class StringList : List<String>{}

and use StringList from XAML.