AVCaptureMetadataOutput，rectOfInterest扫描外部

Question

所以我正在尝试使用AVCaptureMetadataOutput来扫描QR码。我遇到的问题是扫描可能发生在预览区域之外，即使我使用rectOfInterest看到下图：

以下是代码：

- (void)capture
{

session = [[AVCaptureSession alloc] init];
device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

if ( [device lockForConfiguration:NULL] == YES ) {

    CGPoint point = CGPointMake(0.5,0.5);
    [device setFocusPointOfInterest:point];
    [device setFocusMode:AVCaptureFocusModeContinuousAutoFocus];
    [device unlockForConfiguration];

}

NSError *error = nil;

AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
                                                                    error:&error];
if (!input)
{
    NSLog(@"Error: %@", error);
    return;
}

[session addInput:input];


//Add the metadata output device
output = [[AVCaptureMetadataOutput alloc] init];
[output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[session addOutput:output];

output.metadataObjectTypes = @[AVMetadataObjectTypeQRCode, AVMetadataObjectTypeCode128Code];

output.rectOfInterest = self.livevideo.bounds;

newCaptureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
newCaptureVideoPreviewLayer.frame = self.livevideo.bounds;
newCaptureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[self.livevideo.layer insertSublayer:newCaptureVideoPreviewLayer above:self.livevideo.layer];

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

[session startRunning];

}

- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputMetadataObjects:(NSArray *)metadataObjects
   fromConnection:(AVCaptureConnection *)connection
{
AVMetadataMachineReadableCodeObject *barCodeObject;
CGRect highlightViewRect = CGRectZero;

for (AVMetadataObject *metadata in metadataObjects)
{

    for (NSString *type in output.metadataObjectTypes) {
        if ([metadata.type isEqualToString:type])
        {

            barCodeObject = (AVMetadataMachineReadableCodeObject *)[newCaptureVideoPreviewLayer transformedMetadataObjectForMetadataObject:(AVMetadataMachineReadableCodeObject *)metadata];

            highlightViewRect = barCodeObject.bounds;
            @try {
                NSString *code =[barCodeObject stringValue];
                NSLog(@"Read  type: %@", type);
                self.barcode.text = code;
            }
            @catch (NSException *exception) {
                NSLog(@"%@", exception.reason);
            }

            break;
        }
    }

}

highlightView.frame = highlightViewRect;
}

Answer 1

那是documented behavior：

  

不会返回其边界与rectOfInterest不相交的元数据对象。

因此，如果QR码与矩形相交，则会检测到它。