iOS app crashes while touching screen for autofocus in camera

Question

In my app I am scanning QR codes using camera, In case if user touches screen it should autofocus at that point but sometimes app crashes. Here is code for that function in which app crashes at code line device.focusPointOfInterest = focusPoint

/** Touch the screen for autofocus */
    public override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard touches.first?.view == view,
              let touchPoint = touches.first,
              let device = videoCaptureDevice
        else { return }
        
        let videoView = view
        let screenSize = videoView!.bounds.size
        let xPoint = touchPoint.location(in: videoView).y / screenSize.height
        let yPoint = 1.0 - touchPoint.location(in: videoView).x / screenSize.width
        let focusPoint = CGPoint(x: xPoint, y: yPoint)
        
        do {
            try device.lockForConfiguration()
        } catch {
            return
        }
        
        // Focus to the correct point, make continiuous focus and exposure so the point stays sharp when moving the device closer
        device.focusPointOfInterest = focusPoint
        device.focusMode = .continuousAutoFocus
        device.exposurePointOfInterest = focusPoint
        device.exposureMode = AVCaptureDevice.ExposureMode.continuousAutoExposure
        device.unlockForConfiguration()
    }

Logs for crashes (only relevant part is attached)

Last Exception Backtrace:
0   CoreFoundation                  0x180f37c60 __exceptionPreprocess + 216 
(NSException.m:200)
1   libobjc.A.dylib                 0x198767ee4 objc_exception_throw + 56 (objc- 
exception.mm:565)
2   AVFCapture                      0x1a45297f4 -[AVCaptureFigVideoDevice         
setFocusPointOfInterest:] + 276 (AVCaptureFigVideoDevice.m:0)
3   QR Code Creator Scanner         0x1021f13bc specialized 
CodeScannerView.ScannerViewController.touchesBegan(_:with:) + 508 
(CodeScannerView.swift:307)
4   QR Code Creator Scanner         0x1021f010c 
CodeScannerView.ScannerViewController.touchesBegan(_:with:) + 12 (<compiler- 
generated>:0)
5   QR Code Creator Scanner         0x1021f010c @objc 
CodeScannerView.ScannerViewController.touchesBegan(_:with:) + 120
6   UIKitCore                       0x1833c099c forwardTouchMethod + 316 
(UIResponder.m:2039)
7   UIKitCore                       0x183341ed0 -[UIWindow _sendTouchesForEvent:] + 
624 (UIWindow.m:2960)

The Line of code causing crash is

 device.focusPointOfInterest = focusPoint

I am not ale to understand actual reason of crash.

Answer 1

Please check if CGPoint is valid or not or check if Device Supports Focus ?

I'm updating code check if it works in your case

public override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
guard let touch = touches.first,
      touch.view == view,
      let device = videoCaptureDevice,
      device.isFocusModeSupported(.continuousAutoFocus),
      device.isExposureModeSupported(.continuousAutoExposure) else {
    return
}

let videoView = view
let screenSize = videoView!.bounds.size
let xPoint = touch.location(in: videoView).y / screenSize.height
let yPoint = 1.0 - touch.location(in: videoView).x / screenSize.width
let focusPoint = CGPoint(x: xPoint, y: yPoint)

do {
    try device.lockForConfiguration()
    if device.isFocusPointOfInterestSupported {
        device.focusPointOfInterest = focusPoint
        device.focusMode = .continuousAutoFocus
    }
    if device.isExposurePointOfInterestSupported {
        device.exposurePointOfInterest = focusPoint
        device.exposureMode = .continuousAutoExposure
    }
    device.unlockForConfiguration()
} catch {
    print("Failed to lock device configuration: \(error)")
  }
}