Jun 25, 2009

Cancel Hanlder

The cancel handler view provides a way to define activity cancellation logic. A cancel handler has some similarities to the fault handlers just discussed. Like fault handlers, they are attached only to a composite activity.However, cancel handlers don’t catch and handle exceptions. Instead, they specify the cleanup actions that take place when an executing activity is canceled.

actions that take place when an executing activity is canceled. The need for cancel handlers is best illustrated with an example: A ListenActivity is a composite activity that allows you to define multiple child activities under it. Assume that each child of the ListenActivity is a HandleExternalEventActivity that listens for a different external event. With this scenario, each HandleExternalEventActivity is executing at the same time waiting for an event. Only one of these children will eventually receive its event and complete execution. The other sibling activities will be canceled by the ListenActivity parent. By entering a cancel handler for the parent ListenActivity, you define the steps to execute when the incomplete children are canceled. You won’t always need a cancel handler. But if your activities require any cleanup when they are canceled, a cancel handler is an appropriate place to define that logic.