We have seen how Radical Presentation resolves views instances at runtime and we have told that during the resolution process we inject/attach to the resolved view some behaviors using a convention.
The convention attaches the following behaviors to each resolved view:
- to every view (every DependencyObject) attaches the “DependencyObjectCloseHandlerBehavior” whose role is to allow the view model to send a close request message to its own view without the need to handle a reference to the view;
- if the view is a window attaches the “WindowLifecycleNotificationsBehavior” used to notify to the view model the lifecycle state changes of the view (loaded, shown, activated, closing and closed);
- “else if” the view is a FrameworkElement attaches the “FrameworkElementLifecycleNotificationsBehavior” whose role is notify to the view model when the view is loaded;
The easiest way to handle view lifecycle state changes in the ViewModel is to setup a callback expectation.
The WindowLifecycleNotificationsBehavior whenever the view is closed invokes ViewReleaseHandler convention that is responsible to determine if the ViewModel associated with the closed View should be unsubscribed from all the message broker subscriptions, if any, created.