如何绑定到 UIElement

Question

I am trying to pass the parent Window in to a command so that it can be used for a RoutedCommand . Is there any way to do this with Dependency Properties ? Ive seen a lot of questions that say this isn't possible because it isn't part of the visual tree, but the below works:

<Button CommandParameter="{Binding ElementName=Main}" .../>

The parameter is actually set as Main (the parent Window). So, how can I do this on my custom object with a Dependency Property ?

The error I get when I try to set it on my own object DP:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:(no path); DataItem=null; target element is 'CommandGroup' (HashCode=25702951); target property is 'CommandParameter' (type 'Object')

My class is as follows:

public class CommandGroup : DependencyObject, ICommand
{
  public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register("CommandParameter", typeof (object), typeof (CommandGroup));

  public object CommandParameter
  {
    get { return (object)GetValue(CommandParameterProperty); }
    set { SetValue(CommandParameterProperty, value); }
  }

  ....
}

I want to set the XAML as below:

<Button>
  <Button.Command>
    <CommandGroup CommandParameter={Binding ElementName=Main}>
    ...

Answer 1

Because CommandParameter is not a visual or logical tree element, it cannot inherit DataContext.

...but when your object is Freezable , it can inherit DataContext.

public class CommandGroup : Freezable, ICommand
{
    public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register("CommandParameter", typeof (object), typeof (CommandGroup));

    public object CommandParameter
    {
        get { return (object)GetValue(CommandParameterProperty); }
        set { SetValue(CommandParameterProperty, value); }
    }

    protected override Freezable CreateInstanceCore()
    {
        return new CommandGroup();
    }
}

See: https://thomaslevesque.com/2011/03/21/wpf-how-to-bind-to-data-when-the-datacontext-is-not-inherited/