Skip to main content

Generic types in XAML

Avalonia supports using generic .NET types in XAML through the x:TypeArguments directive. This allows you to instantiate generic classes and use generic collections directly in markup.

x:TypeArguments​

The x:TypeArguments directive specifies the type arguments for a generic type. It can only be used on the root element of a XAML file or on elements that also have x:Class or are inside a resource dictionary.

Basic syntax​

<local:MyGenericControl x:TypeArguments="x:String" />

Multiple type arguments​

Separate multiple type arguments with commas:

<local:Pair x:TypeArguments="x:String, x:Int32" />

Using generic collections in resources​

You can define generic collections as resources:

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:sys="using:System"
        xmlns:scg="using:System.Collections.Generic">

    <Window.Resources>
        <scg:List x:Key="Colors" x:TypeArguments="sys:String">
            <sys:String>Red</sys:String>
            <sys:String>Blue</sys:String>
            <sys:String>Green</sys:String>
        </scg:List>
    </Window.Resources>

    <ListBox ItemsSource="{StaticResource Colors}" />
</Window>

Generic custom controls​

When creating a generic custom control, define the type parameter in C#:

public class TypedList<T> : ItemsControl
{
    public static readonly StyledProperty<T?> SelectedValueProperty =
        AvaloniaProperty.Register<TypedList<T>, T?>(nameof(SelectedValue));

    public T? SelectedValue
    {
        get => GetValue(SelectedValueProperty);
        set => SetValue(SelectedValueProperty, value);
    }
}

Use it in XAML with x:TypeArguments:

<local:TypedList x:TypeArguments="vm:Person" ItemsSource="{Binding People}" />

Common generic types in XAML​

TypeXAML PrefixExample
System.Stringx:Stringx:TypeArguments="x:String"
System.Int32x:Int32x:TypeArguments="x:Int32"
System.Doublex:Doublex:TypeArguments="x:Double"
System.Booleanx:Booleanx:TypeArguments="x:Boolean"
Custom typeslocal: or vm:x:TypeArguments="vm:MyModel"

Limitations​

  • x:TypeArguments on the root element requires x:Class to also be specified.
  • Nested generic types (e.g., List<List<string>>) are not supported in XAML. Define them in code and reference via binding or x:Static.
  • Not all XAML contexts support x:TypeArguments. It works on object elements and resource definitions.

Workarounds for unsupported scenarios​

When XAML generics are not practical, define a concrete subclass:

// Define a non-generic subclass for use in XAML
public class StringList : List<string> { }
public class PersonCollection : ObservableCollection<Person> { }
<!-- Use the concrete type directly -->
<local:StringList x:Key="Names">
    <sys:String>Alice</sys:String>
    <sys:String>Bob</sys:String>
</local:StringList>

This pattern is common in .NET XAML frameworks and avoids any x:TypeArguments limitations.

See also​

On this page