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XAML namespaces

XAML namespaces tell the XAML engine where to find the types referenced in your markup. Every Avalonia XAML file requires at least one namespace declaration to work.

Default namespaces​

A typical Avalonia XAML file starts with two namespace declarations:

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
</Window>
DeclarationPurpose
xmlns="https://github.com/avaloniaui"The default Avalonia namespace. Maps to all core Avalonia CLR namespaces (Avalonia, Avalonia.Controls, Avalonia.Media, Avalonia.Animation, and others). Required in every Avalonia XAML file.
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"The XAML language namespace. Provides access to x: directives like x:Name, x:Key, and x:Class.

CLR namespaces mapped to the default Avalonia namespace​

The https://github.com/avaloniaui URI maps to many CLR namespaces across Avalonia assemblies. The most commonly used include:

  • Avalonia (base types)
  • Avalonia.Controls (all standard controls)
  • Avalonia.Controls.Primitives
  • Avalonia.Controls.Shapes
  • Avalonia.Controls.Presenters
  • Avalonia.Controls.Templates
  • Avalonia.Controls.Documents
  • Avalonia.Controls.Notifications
  • Avalonia.Animation
  • Avalonia.Animation.Easings
  • Avalonia.Data (binding types)
  • Avalonia.Media (brushes, transforms, geometries)
  • Avalonia.Layout
  • Avalonia.Styling
  • Avalonia.Markup.Xaml.MarkupExtensions
  • Avalonia.Markup.Xaml.Styling
  • Avalonia.Markup.Xaml.Templates

Referencing your own types​

To use your own classes in XAML, you need to declare a namespace prefix that maps to a CLR namespace.

Using the using: prefix​

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:MyApp.ViewModels"
        xmlns:controls="using:MyApp.Controls">

    <controls:MyCustomControl DataContext="{x:Static vm:DesignData.MainViewModel}" />
</Window>

The using: prefix works for namespaces in the current assembly or any referenced assembly. This is the recommended syntax.

Using the clr-namespace: prefix​

The clr-namespace: prefix, familiar from WPF, is also supported:

Same assembly:

xmlns:local="clr-namespace:MyApp.Controls"

Different assembly:

xmlns:ext="clr-namespace:ThirdParty.Controls;assembly=ThirdParty.Controls"
tip

Prefer using: over clr-namespace:. The using: syntax is shorter and does not require the ;assembly= suffix for referenced assemblies.

Defining custom XML namespace mappings​

Library authors can map multiple CLR namespaces to a single XML namespace URI using the XmlnsDefinition assembly attribute:

// In your library's AssemblyInfo.cs or a Properties file
[assembly: XmlnsDefinition("https://mycompany.com/mylib", "MyLib.Controls")]
[assembly: XmlnsDefinition("https://mycompany.com/mylib", "MyLib.Converters")]
[assembly: XmlnsDefinition("https://mycompany.com/mylib", "MyLib.Panels")]

Users of the library can then use a single namespace declaration:

<Window xmlns:mylib="https://mycompany.com/mylib">
    <mylib:FancyButton />
</Window>

Common namespace prefixes by convention​

These prefixes are commonly used across Avalonia projects:

PrefixTypical Mapping
xXAML language namespace
dhttp://schemas.microsoft.com/expression/blend/2008 (design-time)
mchttp://schemas.openxmlformats.org/markup-compatibility/2006
localThe application's root namespace
vmViewModels namespace
convConverters namespace

Design-time namespaces​

The d: and mc: namespaces enable design-time features:

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        d:DesignWidth="800" d:DesignHeight="450">
</Window>
  • d:DesignWidth and d:DesignHeight set the preview size in the XAML designer.
  • d:DataContext sets a design-time data context for binding previews.
  • mc:Ignorable="d" tells the runtime to ignore all d: attributes.

See also​

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