Message broker MVVM built-in messages

Radical Presentation relies on the MessageBroker to broadcast messages that can be used by the application to easily manage a lot of stuff that otherwise can be a bit cumbersome.

The following is the list of the Radical Presentation built-in messages and their meaning/usage.

Application Messages

These messages are broadcasted or dispatched by the application to notify application level state changes.

• ApplicationBootCompleted:

  • broadcasted asynchronously by application bootstrapper to notify that the boot process is completed.

• ApplicationShutdownRequest:

  • can be dispatched or broadcasted by anyone to request programmatically the application to shutdown. it is highly recommended that the message is broadcasted asynchronously_._ When the application shutdown is requested via the ApplicationShutdownRequest message, the following events might be dispatched:

    • ApplicationShutdownRequested:

      • dispatched synchronously by application bootstrapper to notify that the application has started the shutdown process, this event is dispatched synchronously to allow subscribers to easily cancel the shutdown process using a well known approach similar to the one exposed by the .net CancelEventArgs.

    • ApplicationShutdownCanceled:

      • broadcasted asynchronously by application bootstrapper to notify that the shutdown process has been canceled.

• ApplicationShutdown:

  • broadcasted asynchronously by application bootstrapper to notify that the shutdown process is in progress, from this point on the process is not cancellable any more.

Note:

All the “application shutdown” related events/messages brings with them an enumeration (ApplicationShutdownReason) that identifies why the application is shutting down.

View/ViewModel Messages

The following messages are broadcasted or dispatched by the infrastructure when the state of a view changes or to request a change to the view status.

• CloseViewRequest:

  • can be dispatched or broadcasted by anyone to request programmatically to a view to close. it is highly recommended that the message is broadcasted asynchronously. The message is generally used to close the view of the view model that issues the message, but the shape of the message allows to close a view attached to any view model.

  class SampleViewModel
  {
      readonly IMessageBroker broker;
  
      public SampleViewModel( IMessageBroker broker )
      {
          this.broker = broker;
      }
  
      public void Sample()
      {
          this.broker.Broadcast( this, new CloseViewRequest( this ) );
      }
  }

• ViewModelClosed:

  • broadcasted asynchronously by the infrastructure to notify that a view and an associated ViewModel has been closed.

• ViewModelClosing:

  • dispatched synchronously by the infrastructure to notify that the a view and an associated ViewModel is closing, this event is dispatched synchronously to allow subscribers to easily cancel the close process using a well known approach similar to the one exposed by the .net CancelEventArgs.

• ViewLoaded:

  • broadcasted asynchronously by the infrastructure to notify that a view has been loaded.

• ViewModelLoaded:

  • broadcasted asynchronously by the infrastructure to notify that a ViewModel has been loaded.

Note:

ViewLoaded and ViewModelLoaded messages are broadcasted only under certain circumstances, depending on the result of the ShouldNotifyViewLoaded and ShouldNotifyViewModelLoaded conventions.

• ViewModelShown:

  • broadcasted asynchronously by the infrastructure to notify that a view and an associated ViewModel has been shown for the first time.