iOS：导航后 AVCaptureOutput 停止工作

Question

我将摄像头视图用作条形码扫描仪，它可以扫描条形码并使用 Web 视图启动到另一个 viewcontroller 的 segue。这工作正常，我可以从网络视图导航回扫描仪并扫描另一个条形码而不会出现问题。但是，如果我离开带有摄像头的视图控制器并 return 导航到它，摄像头视图会加载但不再检测条形码。

@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

所以我已经设法解决了这个问题，但无法真正理解它的工作原理。

我没有在 viewDidLoad 期间异步加载 URL，而是通过 segue 传递 URL 并从包含 WebView 的 ViewController 中加载它。

除此之外，变量声明被封装在花括号 {} 中并且 @synthesize mWebView 被移除。我不知道为什么这会导致问题，所以任何可能的解释将不胜感激

iOS：导航后 AVCaptureOutput 停止工作

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ios

objective-c

avcapturesession

avcaptureoutput