如何在Prism 4中为DelegateCommand启用KeyBinding？

<Grid.InputBindings>
        <KeyBinding Gesture="CTRL+A" Command="{Binding Command3}"/>
</Grid.InputBindings>

<StackPanel>
   <Button Grid.Row="0" Grid.Column="1" Content="HitMe" prism:Click.Command="{Binding  Command3}" />
</StackPanel>

public DelegateCommand<string> Command3 { get; private set; }

    private void ExecuteCommand3(string commandParameter)
    {
        Debug.WriteLine("ExecuteCommand3");

    }

    private bool CanExecuteCommand3(string commandParameter)
    {
        return true;
    }