iOS: AVCaptureOutput stops working after navigation - ios

Question

I'm using the camera view as a barcode scanner that scans a barcode and launches a segue to another viewcontroller with a webview. This is working fine, and I can navigate back to the scanner from the webview and scan another barcode without issue. However, if I navigate away from the view controller with the camera and return to it, the camera view loads but no longer detects barcodes.
#implementation ProductScanViewController
NSString *loadUrl;
AVCaptureSession *_captureSession;
AVCaptureDevice *_videoDevice;
AVCaptureDeviceInput *_videoInput;
AVCaptureVideoPreviewLayer *_previewLayer;
BOOL _running;
AVCaptureMetadataOutput *_metadataOutput;
#synthesize mWebView;
- (void)viewDidLoad {
[super viewDidLoad];
NSURL *url = [NSURL URLWithString:loadUrl];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSOperationQueue *queue = [[NSOperationQueue alloc]init];
[NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{if([data length] > 0 && error == nil)[mWebView loadRequest:request]; else if (error != nil) NSLog(#"Error: %", error);}
];
[self setupCaptureSession];
}
- (void)setupCaptureSession {
// 1
if (_captureSession){
return;
}
// 2
_videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
if (!_videoDevice) {
return;
}
// 3
_captureSession = [[AVCaptureSession alloc] init];
// 4
_videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:_videoDevice error:nil];
// 5
if ([_captureSession canAddInput:_videoInput]) {
[_captureSession addInput:_videoInput];
}
// 6
_previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
_previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
// capture and process the metadata
_metadataOutput = [[AVCaptureMetadataOutput alloc] init];
dispatch_queue_t metadataQueue =
dispatch_queue_create("com.1337labz.featurebuild.metadata", 0);
[_metadataOutput setMetadataObjectsDelegate:self
queue:metadataQueue];
if ([_captureSession canAddOutput:_metadataOutput]) {
[_captureSession addOutput:_metadataOutput];
}
}
#pragma mark - Delegate functions
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputMetadataObjects:(NSArray *)metadataObjects
fromConnection:(AVCaptureConnection *)connection {
[metadataObjects enumerateObjectsUsingBlock:^(AVMetadataObject *obj,
NSUInteger idx,
BOOL *stop) {
if ([obj isKindOfClass: [AVMetadataMachineReadableCodeObject class]]) {
//NSLog(#"Capture Output started");
// 3
AVMetadataMachineReadableCodeObject *code = (AVMetadataMachineReadableCodeObject*)
[_previewLayer transformedMetadataObjectForMetadataObject:obj];
// 4
Barcode * barcode = [Barcode processMetadataObject:code];
for (NSString * str in self.allowedBarcodeTypes) {
if([barcode.getBarcodeType isEqualToString:str]){
[self validBarcodeFound:(barcode)];
return;
}
}
}
}];
}
- (void) validBarcodeFound:(Barcode *)barcode{
NSLog(#"Found Barcode");
[self stopRunning];
[self.foundBarcodes addObject:barcode];
//[self showBarcodeAlert:barcode];
NSString *alertMessage = #"";
alertMessage = [alertMessage stringByAppendingString:[barcode getBarcodeType]];
NSLog([barcode getBarcodeData]);
NSLog(alertMessage);
NSLog([NSString stringWithFormat:#"%#", barcode.getBarcodeData]);
if ([barcode.getBarcodeType isEqualToString:#"org.iso.QRCode"])
{
if ([[NSString stringWithFormat:#"%lu",(unsigned long)[self.foundBarcodes count]-1] length] > 0){
NSString *input = [barcode getBarcodeData];
[NSString stringWithFormat:#"%lu",(unsigned long)[self.foundBarcodes count]-1];
NSLog(input);
if ([input length] >= 13)
{
input = [input substringToIndex:12];
}
loadUrl = [[#"http://www.mywebsite.co.uk/" stringByAppendingString:input] stringByAppendingString:#"?utm_source=iphone"];
NSLog(loadUrl);
dispatch_sync(dispatch_get_main_queue(), ^{
[self performSegueWithIdentifier:#"toWebView" sender:self];
});
}
}

Answer 1

So I've managed to fix this but can't give any real understanding of why it works.
Instead of loading the URL asynchronously during viewDidLoad, I passed the URL with the segue and loaded it from within the ViewController containing the WebView.
Further to this, the variable declarations were encapsulated in curly brackets {} and the #synthesize mWebView was removed. I've no idea why that was causing issues so any possible explanation would be appreciated