AppCallbacks class reference

You can use the AppCallbacks class to connect your main application to the Unity engine.

Example: How to use the AppCallbacks class

App.xaml.cpp file

App::App()
{
    InitializeComponent();
    SetupOrientation();
    m_AppCallbacks = ref new AppCallbacks();
}

void App::OnLaunched(LaunchActivatedEventArgs^ e)
{
    m_SplashScreen = e->SplashScreen;
    InitializeUnity(e->Arguments);
}

void App::InitializeUnity(String^ args)
{
    ApplicationView::GetForCurrentView()->SuppressSystemOverlays = true;

    m_AppCallbacks->SetAppArguments(args);
    auto rootFrame = safe_cast<Frame^>(Window::Current->Content);

    // Do not repeat app initialization when the Window already has content,
    // just ensure that the window is active
    if (rootFrame == nullptr && !m_AppCallbacks->IsInitialized())
    {
        rootFrame = ref new Frame();
        Window::Current->Content = rootFrame;
#if !UNITY_HOLOGRAPHIC
        Window::Current->Activate();
#endif

        rootFrame->Navigate(TypeName(MainPage::typeid ));
    }

    Window::Current->Activate();
}

MainPage.xaml.cpp file

MainPage::MainPage()
{
    m_SplashScreenRemovalEventToken.Value = 0;
    m_OnResizeRegistrationToken.Value = 0;

    InitializeComponent();
    NavigationCacheMode = ::NavigationCacheMode::Required;

    auto appCallbacks = AppCallbacks::Instance;

    bool isWindowsHolographic = false;

#if UNITY_HOLOGRAPHIC
    // If application was exported as Holographic check if the device actually supports it
    // Otherwise, we treat this as a normal XAML application
    isWindowsHolographic = AppCallbacks::IsMixedRealitySupported();
#endif

    if (isWindowsHolographic)
    {
        appCallbacks->InitializeViewManager(Window::Current->CoreWindow);
    }
    else
    {
        m_SplashScreenRemovalEventToken = appCallbacks->RenderingStarted += ref new RenderingStartedHandler(this, &MainPage::RemoveSplashScreen);

        appCallbacks->SetSwapChainPanel(m_DXSwapChainPanel);
        // Subscribes to all needed system events
        appCallbacks->SetCoreWindowEvents(Window::Current->CoreWindow);

        // This is the main initialization function for Unity
        // Initializes engine graphics, DirectX, and gamepad and joystick input
        // Loads IL2CPP and all engine subsystems except graphics
        appCallbacks->InitializeD3DXAML();
        // At this point, when Unity finishes loading the first level, it enters the main loop.

        m_SplashScreen = safe_cast<App^>(App::Current)->GetSplashScreen();

        auto dispatcher = CoreWindow::GetForCurrentThread()->Dispatcher;
        ThreadPool::RunAsync(ref new WorkItemHandler([this, dispatcher](IAsyncAction^)
        {
            GetSplashBackgroundColor(dispatcher);
        }));

        OnResize();

        m_OnResizeRegistrationToken = Window::Current->SizeChanged += ref new WindowSizeChangedEventHandler([this](Object^, WindowSizeChangedEventArgs^)
        {
            OnResize();
        });
    }
}

Create an app thread

Unity doesn’t run your app on the UI thread because the UI could become unresponsive when loading large apps. For more information on UI threads, refer to Microsoft documentation on Keeping the UI thread responsive.

When you create the AppCallbacks class using m_AppCallbacks = ref new AppCallbacks();, Unity creates a new thread called App Thread. Unity creates this new thread due to a Microsoft restriction: if your application doesn’t become responsive after 5 seconds, you’ll fail to pass the Windows App Certification Kit tests. For more information, refer to Microsoft documentation on the Windows App Certification Kit.

Note: Code located in the App.xaml.cpp and MainPage.xaml.cpp files always runs on the UI thread, unless called from the InvokeOnAppThread function.

Command line arguments

You can pass custom command line arguments as string arrays into the AppCallbacks constructor. For more information, refer to UWP Command line arguments.

AppCallbacks functions

Additional resources

• Microsoft documentation on Keeping the UI thread responsive
• UWP Command line arguments
• Command line arguments