Fatal Exception: NSInvalidArgumentException *** Can't add a nil AVCaptureInput about mtbbarcodescanner

[mikebuss]

Thanks @jaybowong. It looks like this exception was caused by nil being returned by deviceInputWithDevice:error: instead of a valid AVCaptureDeviceInput.

According to the documentation for this method, it looks like this could happen if the device is no longer available or in use:

This method returns an instance of AVCaptureDeviceInput that can be used to capture data from an AVCaptureDevice in an AVCaptureSession. This method attempts to open the device for capture, taking exclusive control of it if necessary. If the device cannot be opened because it is no longer available or because it is in use, for example, this method returns nil, and the optional outError parameter points to an NSError describing the problem.

It's possible the user granted camera access to your app, started scanning, then rejected permission, and attempted to start scanning again. Another possibility is they were using the camera in another app and quickly switched over to yours, not giving the camera enough time to unlock for use.

Either way, I think this issue highlights an area of MTBBarcodeScanner that can be improved: instead of silently (or loudly, in this case!) failing when errors occur in the AVFoundation methods, I think it should propagate those errors back to the startScanning method so the user of MTBBarcodeScanner can act on the error.

With my latest update, if the deviceInputWithDevice:error: fails with an error, that error will then be available in the two new scanning methods (Note an error parameter has been added):

- (void)startScanningWithError:(NSError **)error;
- (void)startScanningWithResultBlock:(void (^)(NSArray *codes))resultBlock error:(NSError **)error;

Since this changes the method signature, I'm going to release this at MTBBarcodeScanner v3.0.0. Thanks again!

[mikebuss]

This is now in v3.0.0. Thanks!