MVVM View event Viewmodel command binding

Question

I\'m looking for a good (read: simple) example on how to implement event aggregators with Prism. I\'ve never used Prism and I\'m also quite new to MVVM itself.

I hav

Answer 1

all you need for this is the EventToCommand behavior from MVVMLight or from System.Windows.Interactivity (Blend SDK). i would recommend you to take the MVVMLight version because it has some usefull specials:)

<Canvas>
<i:Interaction.Triggers>
    <i:EventTrigger EventName="MouseUp" >
        <i:InvokeCommandAction Command="{Binding YourMouseUpViewModelCommand}" />
    </i:EventTrigger>
</i:Interaction.Triggers>
</Canvas>

EventAggregator from Prism i mostly used for decoupled Viewmodel to Viewmodel communication.

Answer 2

I didn't know PRISM's EventAggregator allowed for event->command binding.

Another option for you in this case is using a "behavior". Here's a decent overview Behaviors: http://wpftutorial.net/Behaviors.html. You can ignore the Blend part of the tutorial; the important part is that you have at least the Blend 3 SDK installed. Here's how I did this:

public class ButtonDoubleClickCommandBehavior : Behavior<Button>
{
    public ICommand DoubleClickCommand
    {
        get { return (ICommand)GetValue(DoubleClickCommandProperty); }
        set { SetValue(DoubleClickCommandProperty, value); }
    }

    public static readonly DependencyProperty DoubleClickCommandProperty =
        DependencyProperty.Register("DoubleClickCommand", typeof(ICommand), typeof(ButtonDoubleClickCommandBehavior));

    protected override void OnAttached()
    {
        this.AssociatedObject.MouseDoubleClick += AssociatedObject_MouseDoubleClick;
    }

    protected override void OnDetaching()
    {
        if (this.AssociatedObject != null)
        {
            this.AssociatedObject.MouseDoubleClick -= AssociatedObject_MouseDoubleClick;
        }
    }

    void AssociatedObject_MouseDoubleClick(object sender, MouseButtonEventArgs e)
    {
        if (DoubleClickCommand != null && DoubleClickCommand.CanExecute(null))
        {
            DoubleClickCommand.Execute(null);
        }
    }
}

You could add another dependency property to the behavior to bind a command parameter so you can execute the command with that parameter; I just used null in my example.

And my XAML:

<Button Content="{Binding Path=Description}" VerticalAlignment="Center" HorizontalAlignment="Stretch" Template="{StaticResource TextBlockButtonTemplate}" Style="{StaticResource ZynCommandButton}" Tag="DescriptionButton">
    <e:Interaction.Behaviors>
        <ZViewModels:ButtonDoubleClickCommandBehavior DoubleClickCommand="{Binding Path=ItemDescriptionCommand}"/>
    </e:Interaction.Behaviors>
</Button>

Answer 3

A more generic way using behaviors is proposed at AttachedCommandBehavior V2 aka ACB and it even supports multiple event-to-command bindings,

Here is a very basic example of use:

<Border local:CommandBehavior.Event="MouseDown"  
        local:CommandBehavior.Command="{Binding DoSomething}"
        local:CommandBehavior.CommandParameter="From the DarkSalmon Border"
/>