WPF UserControl with generic code-behind

Question

I have this code behind:

CustomUserControl.xaml.cs

namespace MyProject
{
    public partial class CustomUserControl<T> : UserControl
    {
        ...
    }
}

and this xaml:

CustomUserControl.xaml

<UserControl x:Class="MyProject.CustomUserControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:sys="clr-namespace:System;assembly=mscorlib">
<Grid>

</Grid>

It doesn't work since the x:Class="MyProject.CustomUserControl" doesn't match the code-behind's generic class definition. Is there some way to make this work?

Answer 1

You can create generic "code-behind" file without XAML-file:

public class CustomUserControl<T>: UserControl
{ }

and than derive from it providing specific class as a parameter:

public partial class SpecificUserControl : CustomUserControl<Presenter>
{
    public SpecificUserControl()
    {
        InitializeComponent();
    }
}

XAML:

<application:CustomUserControl 
     x:TypeArguments="application:Presenter"
     xmlns:application="clr-namespace:YourApplicationNamespace"
...

Unfortunately, it seems that Visual Studio designer doesn't support such generics until Visual Studio 2012 Update 2 (see https://stackoverflow.com/a/15110115/355438)

Answer 2

Haven't found my solution anywhere else so far. The main difference is, that I have got one .xaml file for the generic user control class and not one for each actual user control.

GenericUserControl.xaml.cs

using System.Windows.Controls;

namespace TestGenericUserControl
{
    public abstract partial class GenericUserControl : UserControl
    {
        // If you use event handlers in GenericUserControl.xaml, you have to define 
        // them here as abstract and implement them in the generic class below, e.g.:

        // abstract protected void MouseClick(object sender, MouseButtonEventArgs e);
    }

    public class GenericUserControl<T> : GenericUserControl
    {
        // generic properties and stuff

        public GenericUserControl()
        {
            InitializeComponent();
        }
    }

    // To use the GenericUserControl<T> in XAML, you could define:
    public class GenericUserControlString : GenericUserControl<string> { }
    // and use it in XAML, e.g.:
    // <GenericUserControlString />
    // alternatively you could probably (not sure) define a markup extension to instantiate
    // it directly in XAML
}

GenericUserControl.xaml

<UserControl x:Class="TestGenericUserControl.GenericUserControl"
        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" 
        mc:Ignorable="d">
    <Grid>
        <Label Content="hello" />
    </Grid>
</UserControl>

Answer 3

Unfortunately XAML does not support generic code behind, thou you can walk around this.

See links below:

http://forums.silverlight.net/forums/p/29051/197576.aspx

Can I specify a generic type in XAML (pre .NET 4 Framework)?

May be generic controls will be supported natively in future versions of Visual Studuo with XAML 2009.