Prism and Ribbon: Crossing regions with commands

I am building a composite WPF application with Prism and using the Ribbon Library. One thing I am having a very difficult time with is with region-crossing commands.

For example, I have my ribbon in my 'RibbonRegion' and a grid view in my 'MainRegion'. Lets say I want a button in my ribbon to pop up a message box with the currently selected item in the grid view, how do I do this?

The easy way is using EventAggregator but I fear that if I have a bunch of subscribers hooked up just for button clicks I am just asking for memory leak issues.

Is there a way to have a cross-region command, so that clicking a button in my 'RibbonRegion' will get the selected item in the grid view and pop up a message box with that value?

You can use a System.Windows.Input.RoutedUICommand

First you need to declare your Command as below:

public static class Commands
{
    public static readonly RoutedUICommand TestCommand = new RoutedUICommand("Test Command",
        "Test Command", typeof(Commands));
}

Then in your RibbonRegion xaml:

<my:RibbonButton Command="{x:Static cmd:Commands.TestCommand}" ...

Then in your MainRegion xaml:

<UserControl.CommandBindings>
    <CommandBinding CanExecute="OnTestCanExecute"
                    Command="{x:Static cmd:Commands.TestCommand}"
                    Executed="OnTestExecute" />
</UserControl.CommandBindings>

Then in your xaml.cs:

public void OnTestRouteCanExecute(object sender, System.Windows.Input.CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
    }

    public void OnTestRouteExecute(object sender, System.Windows.Input.ExecutedRoutedEventArgs e)
    {
        // do some stuff here
    }