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# DDDiscoveryExtension

A specification that enables the framework to start and stop the extension’s discovery process.

```
protocol DDDiscoveryExtension : AppExtension
```

## Overview

Your extension adopts this protocol as the primary entry and exit points for device discovery.

The system calls your extension’s [`startDiscovery(session:)`](/documentation/DeviceDiscoveryExtension/DDDiscoveryExtension/startDiscovery(session:)) when <doc://com.apple.documentation/documentation/AVKit/AVRoutePickerView> displays so your extension can include a specific third-party device in the picker. When the picker UI dismisses or the user selects a device, the system calls your extension’s [`stopDiscovery(session:)`](/documentation/DeviceDiscoveryExtension/DDDiscoveryExtension/stopDiscovery(session:)) implementation to instruct it to perform any cleanup.

## Topics

### Controlling discovery

[`func startDiscovery(session: DDDiscoverySession)`](/documentation/DeviceDiscoveryExtension/DDDiscoveryExtension/startDiscovery(session:))

Begins the extension’s device discovery process.

[`func stopDiscovery(session: DDDiscoverySession)`](/documentation/DeviceDiscoveryExtension/DDDiscoveryExtension/stopDiscovery(session:))

Ends the extension’s device discovery process.

### Observing state changes

[`func didReceiveEvent(DDDeviceEvent)`](/documentation/DeviceDiscoveryExtension/DDDiscoveryExtension/didReceiveEvent(_:))

Provides a device event from the system to the extension.

## Relationships

### Inherits From

[`AppExtension`](/documentation/ExtensionFoundation/AppExtension)

---

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