XNA Environment Initialization

When the Windows Phone XAML and XNA project template is used to create a Windows Phone 7.1 hybrid app, a region is generated within the App class for the purpose of initializing the XNA content manager and starting a GameTimer object. By default, a ContentManager is exposed as a public property within your App class, allowing it to be consumed across your application. You can, however, create new instances of the ContentManager class if you want.

When instantiating a ContentManager, it must be passed an IServiceProvider that can later be used to retrieve an IGraphicsDeviceService. The App class implements IServiceProvider, and the IServiceProvider.GetService method implementation returns objects that reside in the ApplicationLifetimeObjects collection.

Because the App class implements the IServiceProvider interface, it is able to pass itself to the ContentManager constructor, providing the ContentManager access to an IGraphicsDeviceService, which, in this case, is a SharedGraphicsDeviceManager. See the following excerpt:

Click here to view code image

#region XNA application initialization

// Performs initialization of the XNA types required for the application.
void InitializeXnaApplication()
{
    // Create the ContentManager
    // so the application can load precompiled assets.
    ContentManager = new ContentManager(this, "Content");

    // Create a GameTimer to pump the XNA FrameworkDispatcher.
    GameTimer frameworkDispatcherTimer = new GameTimer();
    frameworkDispatcherTimer.FrameAction += FrameworkDispatcherFrameAction;
    frameworkDispatcherTimer.Start();
}

// An event handler that pumps the FrameworkDispatcher each frame.
// FrameworkDispatcher is required for a lot of the XNA events and
// for certain functionality such as SoundEffect playback.
void FrameworkDispatcherFrameAction(object sender, EventArgs e)
{
    FrameworkDispatcher.Update();
}

#endregion

The FrameworkDispatcher.Update method triggers event processing in the XNA framework. In a pure XNA app, it is automatically called whenever Game.Update is called. In XAML apps, however, the absence of a Game class means that we rely on a GameTimer instance to raise a manual call to FrameworkDispatcher.Update.