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# uniqueID

A unique identifier for this photo settings instance.

```
var uniqueID: Int64 { get }
```

## Discussion

Creating a [`AVCapturePhotoSettings`](/documentation/AVFoundation/AVCapturePhotoSettings) instance automatically assigns a unique value to this property.

Use this property to track a photo capture request. After you call the [`capturePhoto(with:delegate:)`](/documentation/AVFoundation/AVCapturePhotoOutput/capturePhoto(with:delegate:)) method, the photo capture output calls your delegate object to provide information about the progress and results of the capture. Each delegate method includes a [`AVCaptureResolvedPhotoSettings`](/documentation/AVFoundation/AVCaptureResolvedPhotoSettings) whose [`uniqueID`](/documentation/AVFoundation/AVCapturePhotoSettings/uniqueID) property matches the [`uniqueID`](/documentation/AVFoundation/AVCapturePhotoSettings/uniqueID) value of the [`AVCapturePhotoSettings`](/documentation/AVFoundation/AVCapturePhotoSettings) object you used to request capture.

It is illegal to reuse a [`AVCapturePhotoSettings`](/documentation/AVFoundation/AVCapturePhotoSettings) instance for multiple captures. Calling the [`capturePhoto(with:delegate:)`](/documentation/AVFoundation/AVCapturePhotoOutput/capturePhoto(with:delegate:)) method throws an exception (<doc://com.apple.documentation/documentation/Foundation/NSExceptionName/invalidArgumentException>) if the `settings` object’s [`uniqueID`](/documentation/AVFoundation/AVCapturePhotoSettings/uniqueID) value matches that of any previously used settings object.

---

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