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# ExtensionKit

Make custom UI from an app extension available in a host app, and manage the list of enabled
and disabled app extensions.

## Overview

An app extension is a code bundle that extends the capabilities of the system, or the capabilities
of another app. At the system level, app extensions give you a way to add your custom capabilities
to system features. For example, [widgets](doc://com.apple.documentation/documentation/WidgetKit/Creating-a-Widget-Extension)
display your app’s content in specific locations like the iOS Home Screen and Lock screen. System
features typically provide a custom workflow for building the associated app extension, but still
use this framework to implement support for those features.

If your app supports the incorporation of content from custom app extensions, adopt this framework
and the <doc://com.apple.documentation/documentation/ExtensionFoundation> framework to support that
capability. Adopt `ExtensionKit` in your app extensions and use it to define the views you want to display.
In a host app, use this framework to present the interfaces that app extensions provide. This framework
also provides a view controller to show enabled and disabled app extensions from your app’s interface.

## Topics

### Essentials

[Including extension-based UI in your interface](/documentation/ExtensionKit/including-extension-based-ui-in-your-interface)

Build app extensions that provide a custom UI, and host those views in your app’s interface.

### UI definition

[`AppExtensionScene`](/documentation/ExtensionKit/AppExtensionScene)

An interface you use to provide a specific scene from your app extension’s UI.

[`PrimitiveAppExtensionScene`](/documentation/ExtensionKit/PrimitiveAppExtensionScene)

A type you use to deliver the contents of your app-extension-based UI.

[`AppExtensionSceneBuilder`](/documentation/ExtensionKit/AppExtensionSceneBuilder)

A custom parameter attribute that constructs extension scenes from closures.

### App extension configuration

[`AppExtensionSceneConfiguration`](/documentation/ExtensionKit/AppExtensionSceneConfiguration)

An object you use to configure an app extension that provides a custom UI.

### Host app presentation

[Displaying the app extensions available to your app](/documentation/ExtensionKit/displaying-the-app-extensions-available-to-your-app)

Show the app extensions available to your app, so that people can approve, enable, or disable them.

[`EXHostViewController`](/documentation/ExtensionKit/EXHostViewController)

A view controller that hosts remote views provided by an app extension.

[`EXAppExtensionBrowserViewController`](/documentation/ExtensionKit/EXAppExtensionBrowserViewController)

A view controller that displays an interface to enable or disable the host app’s extensions.


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