Silverlight 4: How to trigger an Animation when TextBlock’s Text is changed during a DataBinding?

Question

I have a user control which datacontext is set to a view model. The user control contains some textblocks and textboxes which are bind to view model's properties. I would like to do a small animation when a view model's property's value changes but I can't seem to find a way to do this in Silverlight.

In WPF we can use properties like NotifyOnTargetUpdated and Binding.TargetUpdated to capture the change but they seem to be missing from Silverlight. In my case the animation isn't based on the property's value, meaning I don't want to start the animation when some property's value is for example 5. Instead the animation should start every time the property's value is changed (to highlight the changed content for the user).

Here's the answer on how to do this in WPF: http://stackoverflow.com/questions/1165862/animate-wpf-text-when-binding-updates-how

But how can I do the same with Silverlight 4?

Answer 1

Hi there,

you should be able to get this done using the new trigger stuff included in Expression Blend 4. There's a whole bunch of ne behaviors/triggers etc. that let you react to changes in the ViewModel, for instance.

From the Expression Blend feature page:

New Behaviors Expression Blend includes the new TranslateZoomRotateBehavior multi-touch Behavior, and a PanningItems control that you can use to scroll between items by using touch. Expression Blend also has a new trigger that responds to a frame change or the pausing or completion of a SketchFlow animation, called the SketchFlowAnimationTrigger. Expression Blend has new sets of Behaviors for dragging items between list boxes, for modifying menu navigation, and for preserving screen states, such as SetDataStoreValueAction and DataStoreChangedTrigger.

An exciting enhancement has been made to the FluidMoveBehavior: if you apply it to different views of the same data item, when the item moves from one view to another (for example, from a list view to a details view), it fluidly animates the transition between the two views.

New Behaviors for use with applications that use the Model-View-ViewModel pattern include the following: CallMethodAction, InvokeCommandAction, and DataStateBehavior. You can use these Behaviors to invoke behavior on your ViewModels, or to respond to changes to their properties.

Conditional Behaviors and the data store You can now build conditional logic into your prototypes and production applications without the need to write code. In fact any action can be associated with a set of conditions that must be met in order to execute the action. The new data store feature enables application variables, such as the current user's role, for example, can be read from and written to so that, effectively, different parts of your application can communicate via this shared state.

New behavior components introduced as part of this feature include the conditions editor that appears in the Properties panel for every action, a SetDataStoreValueAction action that allows you to manipulate values in your data store, and a DataStoreChangedTrigger trigger that fires whenever a chosen property inside the data store is changed.

http://www.microsoft.com/expression/products/Blend_Features.aspx

Cheers, Alex