Question

I’m working on an augmented reality app which uses an AVCaptureVideoPreviewLayer to display the video feed from the device’s camera. If you close and reopen the app (via pressing the Home button, not by force quitting) or put the phone to sleep and then wake it, the AVCaptureVideoPreviewLayer displays a black rectangle instead of the camera’s feed.

I am initializing the capture session as follows in my viewDidLoad:

captureSession = [[AVCaptureSession alloc] init];

AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
if (videoDevice) { 
    NSError *error;
    AVCaptureDeviceInput *videoIn = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    if (!error) {
        if ([captureSession canAddInput:videoIn])
            [captureSession addInput:videoIn];
        else
            NSLog(@"Couldn't add video input");
    } else
        NSLog(@"Couldn't create video input");
} else
    NSLog(@"Couldn't create video capture device");

[captureSession startRunning];

AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:captureSession];
previewLayer.frame = cameraView.bounds;
previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[[cameraView layer] addSublayer:previewLayer];

Answer 1

You will need to observe the interrupt flag of your AVCaptureSession using KVO and react upon it.

From the AVCaptureSession Reference:

interrupted

Indicates whether the receiver has been interrupted. (read-only)

@property(nonatomic, readonly, getter=isInterrupted) BOOL interrupted
Discussion

You can observe the value of this property using key-value observing

Available in iOS 4.0 and later. Declared In AVCaptureSession.h