Question

Now iOS devices has 0~2 cameras. How to detect them?

Answer 1

You iterate through the video devices…

NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
AVCaptureDevice *captureDevice = nil;

for (AVCaptureDevice *device in videoDevices) {
    if (device.position == AVCaptureDevicePositionFront) {
        //FRONT-FACING CAMERA EXISTS
    }
}

Of course you could also do this a bit quicker with a predicate, but i’ll leave that for you to work out ;)…. (HINT: use the filteredArrayUsingPredicate: method on the devicesWithMediaType:)