Application Class


Represents the current application and its available services.

/// [Windows.Foundation.Metadata.ContractVersion(Microsoft.UI.Xaml.WinUIContract, 65536)]
/// [Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
/// [Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
class Application
[Windows.Foundation.Metadata.ContractVersion(typeof(Microsoft.UI.Xaml.WinUIContract), 65536)]
public class Application
Public Class Application
<Application />


The Application class encapsulates an app and provides the following services:

  • app entry point, particularly for various activation contracts
  • app lifetime management
  • app-scoped resources
  • unhandled exception detection

The Application object is typically provided in the initial XAML for App.xaml. The default project templates in Visual Studio generate an App class that derives from Application and provides an entry point where you can add initialization code.

The App class associates itself with the corresponding XAML by calling the generated InitializeComponent method in its constructor. You can add additional initialization code to the App constructor, but you will typically only add code to associate handlers to Application events. For other initialization code, you should override one or more initialization methods such as OnLaunched.

The system handles app lifetime by suspending your app whenever the user switches to another app or to the desktop, and resuming your app whenever the user switches back to it. However, the system can also terminate your app while it is suspended in order to free up resources.

You should handle the Suspending event to save your app state in case of termination, and override the OnLaunched method to restore your app state. You should handle the Resuming event only if you need to refresh any displayed content that might have changed while the app is suspended. You do not need to restore other app state when the app resumes.

Because of its position in the application model, codegen, and activation sequence, Application has some restrictions on its XAML usage:

  • Other than the xmlns declarations and x:Class, no other attribute can appear on the Application root tag.
  • Don't attempt to change x:Class values that come from the project template App.xaml pages, there are additional dependencies on using that naming scheme that exist in the build actions.
  • Don't wire the Application event handlers in XAML. All event wiring should be done in code (usually in the constructor). Also, you generally use method overrides rather than event syntax for an event (for example, you override OnActivated to respond to that phase of the application life cycle.)
  • The only expected properties on an Application instance in XAML is the set of elements to populate the Application.Resources property, using a XAML property element usage. For more info, see Resources. To provide general error handling for any exceptions that your app code doesn't catch, handle the UnhandledException event.


The Application main file must be named App.xaml.

The following events and virtual methods are not automatically invoked by the system when running in a Desktop app:

  • void OnWindowCreated(Windows.UI.Xaml.WindowCreatedEventArgs args)
  • void overridable OnActivated(IActivatedEventArgs args)
  • void overridable OnBackgroundActivated (BackgroundActivatedEventArgs)
  • void overridable OnCachedFileUpdaterActivated (CachedFileUpdaterActivatedEventArgs)
  • void overridable OnFileActivated (FileActivatedEventArgs)
  • void overridable OnFileOpenPickerActivated (FileOpenPickerActivatedEventArgs)
  • void overridable OnFileSavePickerActivated (FileSavePickerActivatedEventArgs)
  • void overridable OnSearchActivated (SearchActivatedEventArgs)
  • void overridable OnShareTargetActivated (ShareTargetActivatedEventArgs)
  • EnteredBackgroundEventHandler EnteredBackground;
  • LeavingBackgroundEventHandler LeavingBackground;
  • EventHandler<Object> Resuming



Initializes a new instance of the Application class.



Gets the Application object for the current application.


Gets an object that declares how the app behaves when run in a debug environment.


Gets or sets the type of visual feedback that an app can use to indicate the UI element with focus.

This property is valid only for input devices that can generate key events, such as a keyboard or Xbox controller.


Gets or sets a value that indicates whether the framework automatically adjusts visual properties when high contrast themes are enabled.


Gets or sets a value that determines the light-dark preference for the overall theme of an app.


Gets a collection of application-scoped resources, such as styles, templates, and brushes.



Shuts down the app.

LoadComponent(Object, Uri)

Loads a XAML file that is located at the specified relative location, and converts it to an instance of the object that is specified by the root element of the XAML file.

LoadComponent(Object, Uri, ComponentResourceLocation)

Loads a XAML file that is located at the specified relative location, and converts it to an instance of the object that is specified by the root element of the XAML file.


Invoked when the application is launched. Override this method to perform application initialization and to create a new window.


Provides the entry point and requests initialization of the application. Use the specified ApplicationInitializationCallback to instantiate the Application class.



Occurs when an exception can be handled by app code, as forwarded from a native-level Windows Runtime error. Apps can mark the occurrence as handled in event data.

Applies to

See also