captureOutput：didOutputMetadataObjects：fromConnection：多次触发多次触发

Question

captureOutput：didOutputMetadataObjects：fromConnection：多次重命名。我需要将扫描值传递给服务器，以便多次调用服务器进行一次扫描

Answer 1

这是同一个问题 Delegate method being invoked multiple times, even after returning to a view

正如Apple文档所说：＆＃34;这种方法可能经常被调用，您的实现应该有效地防止捕获性能问题，包括丢弃的元数据对象＆＃34;。

处理多次调用执行以下操作：

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection
{
    id capturedData;
        if ([metadataObjects count] > 0) {
            // handle your captured data here

            [self performSelectorOnMainThread:@selector(stopReading:) withObject:capturedData waitUntilDone:NO];

        }

}

stopReading：方法看起来（假设您的_session是AVCaptureSession对象而_prevLayer是您之前使用过的AVCaptureVideoPreviewLayer）：

-(void)stopReading:(id) data{
    NSLog(@"stop reading");
    [_session stopRunning];
    _session = nil;
    [_prevLayer removeFromSuperlayer];
// do what you want with captured data
    [self.delegate didScanBarCodeWithContext:data];
}