WPF 从页面内的 UserControl 在 MainWindow 上执行 ICommand

Question

I'm showing a list of Orders, (each Order is a UserControl), in more than one Page. Every time the user left-click the control, main window should load & show the order in a new Page using an ICommand.

x:Name of MainWindow is: mainWindow

MainViewModel

This is de view model associated to the MainWindow.

public class MainViewModel : BaseViewModel
{
    public INavigator Navigator { get; set; }
    public ICommand OpenOrderCommand { get; set; }

    public MainViewModel(INavigator navigator) : base()
    {
        Navigator = navigator;
        OpenOrderCommand = new RelayCommand(OpenOrder);
    }

    private void OpenOrder(object obj)
    {
        // Loads the order from db
    }
}

I've added an InputBindings tag in the UserControl to detect when the user left-click it.

UserControl

<Grid.InputBindings>
    <MouseBinding MouseAction="LeftClick" 
        Command="{Binding DataContext.OpenOrderCommand,
                          RelativeSource={RelativeSource Mode=FindAncestor, 
                          AncestorType={x:Type Window}}}"
        CommandParameter="{Binding OrderId}"/>
</Grid.InputBindings>

But OpenOrderCommand is never fired, and I get a XAML binding failure with this text:

System.Windows.Data Error: 4: Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''. BindingExpression:Path=DataContext.OpenOrderCommand; DataItem=null; target element is 'MouseBinding' (HashCode=20815867); target property is 'Command' (type 'ICommand')

How can I execute a ICommand of MainWindow from a UserControl?

UPDATE

It works fine if I use current Page instead of MainWindow.

<Grid.InputBindings>
    <MouseBinding MouseAction="LeftClick" 
        Command="{Binding DataContext.OpenOrderCommand,
                          RelativeSource={RelativeSource Mode=FindAncestor, 
                          AncestorType={x:Type local:HomePage}}}"
        CommandParameter="{Binding OrderId}"/>
</Grid.InputBindings>

Answer 1

In the error message it says it can't find the binding source. Try to bind it like this:

<Grid.InputBindings>
        <MouseBinding MouseAction="LeftClick" 
                      Command="{Binding OpenOrderCommand}"
                      CommandParameter="{Binding OrderId}"/>
</Grid.InputBindings>

and to set the DataContext like this:

public MainWindow()
{
     InitializeComponent();
     DataContext = new MainViewModel();
}

In my test code the Grid only raised the event when I had explecitly set a value for the Background-Property. Transparent was also a value which worked.