Avalonia 模板里面绑定ViewModel跟WPF写法有些不同。需要单独绑定Command.

WPF里面可以直接按照下面的方法绑定DataContext.

 <Button Content="Button" 
                       Command="{Binding DataContext.ClickCommand, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}}" CommandParameter="{Binding ID}" />

Avalonia得改成下面这样，单独写Command，在DataContexe前面要加上对应VIewMode强制转换。

					<DataTemplate >
						<Button 
							CommandParameter="{Binding Value}"
							Content="{Binding Label}">
							<Button.Command>
								<Binding  Path="((vm:MessagViewModel)DataContext).ButtonClicked" RelativeSource="{RelativeSource AncestorType=Window}" />
							</Button.Command>

						</Button>
					</DataTemplate>