ios - objective-c 停止扫描 AV Foundation

Question

我正在使用 objective-c 和 AV Foundation 来扫描条形码。我下面的代码完全按照我的意愿执行，它会调出相机并扫描条形码并找到条形码。我的问题是当扫描并找到条形码时，我想停止扫描并停止使用相机...我该如何完成？

AVCaptureSession *_session;
    AVCaptureDevice *_device;
    AVCaptureDeviceInput *_input;
    AVCaptureMetadataOutput *_output;
    AVCaptureVideoPreviewLayer *_prevLayer;

    UIView *_highlightView;
    UILabel *_label;

_highlightView = [[UIView alloc] init];
    _highlightView.autoresizingMask = UIViewAutoresizingFlexibleTopMargin|UIViewAutoresizingFlexibleLeftMargin|UIViewAutoresizingFlexibleRightMargin|UIViewAutoresizingFlexibleBottomMargin;
    _highlightView.layer.borderColor = [UIColor greenColor].CGColor;
    _highlightView.layer.borderWidth = 3;
    [self.view addSubview:_highlightView];

    _label = [[UILabel alloc] init];
    _label.frame = CGRectMake(0, self.view.bounds.size.height - 40, self.view.bounds.size.width, 40);
    _label.autoresizingMask = UIViewAutoresizingFlexibleTopMargin;
    _label.backgroundColor = [UIColor colorWithWhite:0.15 alpha:0.65];
    _label.textColor = [UIColor whiteColor];
    _label.textAlignment = NSTextAlignmentCenter;
    _label.text = @"(none)";
    [self.view addSubview:_label];

    _session = [[AVCaptureSession alloc] init];
    _device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    NSError *error = nil;

    _input = [AVCaptureDeviceInput deviceInputWithDevice:_device error:&error];
    if (_input) {
        [_session addInput:_input];
    } else {
        NSLog(@"Error: %@", error);
    }

    _output = [[AVCaptureMetadataOutput alloc] init];
    [_output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    [_session addOutput:_output];

    _output.metadataObjectTypes = [_output availableMetadataObjectTypes];

    _prevLayer = [AVCaptureVideoPreviewLayer layerWithSession:_session];
    _prevLayer.frame = self.view.bounds;
    _prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    [self.view.layer addSublayer:_prevLayer];

    [_session startRunning];

    [self.view bringSubviewToFront:_highlightView];
    [self.view bringSubviewToFront:_label];


- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection
{
    CGRect highlightViewRect = CGRectZero;
    AVMetadataMachineReadableCodeObject *barCodeObject;
    NSString *detectionString = nil;
    NSArray *barCodeTypes = @[AVMetadataObjectTypeUPCECode, AVMetadataObjectTypeCode39Code, AVMetadataObjectTypeCode39Mod43Code,
                              AVMetadataObjectTypeEAN13Code, AVMetadataObjectTypeEAN8Code, AVMetadataObjectTypeCode93Code, AVMetadataObjectTypeCode128Code,
                              AVMetadataObjectTypePDF417Code, AVMetadataObjectTypeQRCode, AVMetadataObjectTypeAztecCode];

    for (AVMetadataObject *metadata in metadataObjects) {
        for (NSString *type in barCodeTypes) {
            if ([metadata.type isEqualToString:type])
            {
                barCodeObject = (AVMetadataMachineReadableCodeObject *)[_prevLayer transformedMetadataObjectForMetadataObject:(AVMetadataMachineReadableCodeObject *)metadata];
                highlightViewRect = barCodeObject.bounds;
                detectionString = [(AVMetadataMachineReadableCodeObject *)metadata stringValue];
                break;
            }
        }

        if (detectionString != nil)
        {
            _label.text = detectionString;
            //[_session stopRunning];
            break;
        }
        else
            _label.text = @"(none)";
    }

    _highlightView.frame = highlightViewRect;
}

Answer 1

做与开始时相反的事情。你说:

[_session startRunning];

现在说:

[_session stopRunning];

你说:

[self.view.layer addSublayer:_prevLayer];

现在说:

[_prevLayer removeFromSuperlayer];