Running animations in MVVM

We implement Composite application guidance (Prism v2) in our application. Recently we wanted to run animations when something changes in ViewModel. The Viewmodel changes should initiate storyboards or run functions on view.xaml code behind.

I implemented a class ViewModelChangeDispatcher which can be useful to run animations.
You can instantiate this lightweight class from xaml as

OnSourceChangedStartStoryboard="XXXStoryBoard" />

The above VMCD is bound to Source xxxAnimation, this when changed will automatically call the storyboard...

If you want to manage multiple animations using the same, u can handle that by this code

When source is changed the event handler RunAnimation is called.

Anyway here is how I implemented ViewModelChangeDispatcher.

public class ViewModelChangeDispatcher : FrameworkElement
{
#region Data

public static readonly DependencyProperty SourceProperty;
public static readonly DependencyProperty OnSourceChangedStartStoryboardProperty;

// The routed event
public static RoutedEvent SourceChangedEvent;

#endregion // Data

#region Static Constructor and static methods


static ViewModelChangeDispatcher()
{
SourceProperty = DependencyProperty.Register(
"Source",
typeof(String),
typeof(ViewModelChangeDispatcher),
new FrameworkPropertyMetadata(string.Empty,OnSourcePropertyChanged));



OnSourceChangedStartStoryboardProperty = DependencyProperty.Register(
"OnSourceChangedStartStoryboard",
typeof(Storyboard),
typeof(ViewModelChangeDispatcher));


//Registering the events
SourceChangedEvent = EventManager.RegisterRoutedEvent("SourceChanged",
RoutingStrategy.Bubble,
typeof(RoutedEventHandler),
typeof(ViewModelChangeDispatcher));

}

private static void OnSourcePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{

ViewModelChangeDispatcher vmcd = d as ViewModelChangeDispatcher;
if (vmcd == null) return;

vmcd.RaiseEvent(new RoutedEventArgs(SourceChangedEvent, vmcd));
if (vmcd.OnSourceChangedStartStoryboard == null) return;
vmcd.OnSourceChangedStartStoryboard.Begin();
}



#endregion

#region constructor and members
public ViewModelChangeDispatcher()
{
this.Visibility = Visibility.Collapsed;
this.Width = 0;
this.Height = 0;


}

/*
* Source is always string.
* It is the onus of the markupextension to convert it to a string.
*
* */
public String Source
{
get { return (String)GetValue(SourceProperty); }
set { SetValue(SourceProperty, value); }
}



public event RoutedEventHandler SourceChanged
{
add { AddHandler(SourceChangedEvent, value); }
remove { RemoveHandler(SourceChangedEvent, value); }
}

public Storyboard OnSourceChangedStartStoryboard
{
get { return (Storyboard)GetValue(OnSourceChangedStartStoryboardProperty); }
set { SetValue(OnSourceChangedStartStoryboardProperty, value); }
}
#endregion


}

Please let me know if you have any comments/inputs!

Happy coding!
Pradeep Mahdevu

www.pradeepmahdevu.blogspot.com


Also refer Josh Twist's point of view on this.
joy of code and pavan's post here...

Pixel in genie