You can use the DataStoreChangedTrigger trigger to invoke an action based on a modification to a data store.
To add a DataStoreChangedTrigger to a Windows Phone project
In the Assets panel, click Behaviors, and then drag the behavior that you want onto the object that you want to apply the behavior to. The Trigger category appears in the Properties panel.
In the Trigger category, next to TriggerType (EventTrigger), click New. In the Select Object dialog box, click DataStoreChangedTrigger, and then click OK.
In the Property drop-down list, select a property from the list of properties in your data store. When a change to the value of that property is made, the DataStoreChangedTrigger invokes any actions associated with it.
To see a sample of this trigger, visit the Expression Community Gallery .