How To Bind to a Control

With Avalonia UI, as well as binding to a data context you can also bind one control directly to another.

к сведению

Note that this technique does not use a data context at all. When you do this, you are binding directly to another control itself.

Binding to a Named Control

If you want to bind to a property on another named control, you can use the control name prefixed by a # character.

<TextBox Name="other">

<!-- Binds to the Text property of the "other" control -->
<TextBlock Text="{Binding #other.Text}"/>

This is the equivalent to the long-form binding that will be familiar to WPF and UWP users:

<TextBox Name="other">
<TextBlock Text="{Binding Text, ElementName=other}"/>

Avalonia UI supports both syntaxes.

Binding to an Ancestor

You can bind to the (logical control tree) parent of the target using the $parent syntax:

<Border Tag="Hello World!">
  <TextBlock Text="{Binding $parent.Tag}"/>
</Border>

Or to any level of ancestor by using an index with the $parent syntax:

<Border Tag="Hello World!">
  <Border>
    <TextBlock Text="{Binding $parent[1].Tag}"/>
  </Border>
</Border>

The index is zero based so $parent[0] is equivalent to $parent.

You can also bind to the closest ancestor of a given type, like this:

<Border Tag="Hello World!">
  <Decorator>
    <TextBlock Text="{Binding $parent[Border].Tag}"/>
  </Decorator>
</Border>

Finally, you can combine the index and the type:

<Border Tag="Hello World!">
  <Border>
    <Decorator>
    <TextBlock Text="{Binding $parent[Border;1].Tag}"/>
    </Decorator>
  </Border>
</Border>

If you need to include a XAML namespace in the ancestor type, you separate the namespace and class using a colon, like this:

<local:MyControl Tag="Hello World!">
  <Decorator>
    <TextBlock Text="{Binding $parent[local:MyControl].Tag}"/>
  </Decorator>
</local:MyControl>

'To access a property of a parent's DataContext it will be necessary to cast it with a casting expression (vm:MyUserControlViewModel)DataContext to its actual type. Otherwise DataContext would be considered as of type object and accessing a custom property would result in an compile-time error.

<local:MyControl Tag="Hello World!">
  <Decorator>
    <TextBlock Text="{Binding $parent[local:MyControl].((vm:MyUserControlViewModel)DataContext).CustomProperty}"/>
  </Decorator>
</local:MyControl>

warning

Avalonia UI also supports WPF/UWP's RelativeSource syntax which does something similar, but is not the same. RelativeSource works on the visual tree whereas the syntax given here works on the logical tree.