iOS使用AVFoundation实现二维码扫描

    #import <AVFoundation/AVFoundation.h>

    static const char *kScanQRCodeQueueName = "ScanQRCodeQueue";

    @interface ViewController () <AVCaptureMetadataOutputObjectsDelegate>
    .....
    @property (nonatomic) AVCaptureSession *captureSession;
    @property (nonatomic) AVCaptureVideoPreviewLayer *videoPreviewLayer;
    @property (nonatomic) BOOL lastResult;
    @end

    - (BOOL)startReading
    {
        // 获取 AVCaptureDevice 实例
        NSError * error;
        AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
        // 初始化输入流
        AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:&error];
        if (!input) {
            NSLog(@"%@", [error localizedDescription]);
            return NO;
        }
        // 创建会话
        _captureSession = [[AVCaptureSession alloc] init];
        // 添加输入流
        [_captureSession addInput:input];
        // 初始化输出流
        AVCaptureMetadataOutput *captureMetadataOutput = [[AVCaptureMetadataOutput alloc] init];
        // 添加输出流
        [_captureSession addOutput:captureMetadataOutput];

        // 创建dispatch queue.
        dispatch_queue_t dispatchQueue;
        dispatchQueue = dispatch_queue_create(kScanQRCodeQueueName, NULL);
        [captureMetadataOutput setMetadataObjectsDelegate:self queue:dispatchQueue];
        // 设置元数据类型 AVMetadataObjectTypeQRCode
        [captureMetadataOutput setMetadataObjectTypes:[NSArray arrayWithObject:AVMetadataObjectTypeQRCode]];

        // 创建输出对象
        _videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
        [_videoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
        [_videoPreviewLayer setFrame:_sanFrameView.layer.bounds];
        [_sanFrameView.layer addSublayer:_videoPreviewLayer];
        // 开始会话
        [_captureSession startRunning];

        return YES;
    }

    - (void)stopReading
    {
        // 停止会话
        [_captureSession stopRunning];
        _captureSession = nil;
    }

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects
  fromConnection:(AVCaptureConnection *)connection
{
    if (metadataObjects != nil && [metadataObjects count] > 0) {
        AVMetadataMachineReadableCodeObject *metadataObj = [metadataObjects objectAtIndex:0];
        NSString *result;
        if ([[metadataObj type] isEqualToString:AVMetadataObjectTypeQRCode]) {
            result = metadataObj.stringValue;
        } else {
            NSLog(@"不是二维码");
        }
        [self performSelectorOnMainThread:@selector(reportScanResult:) withObject:result waitUntilDone:NO];
    }
}

  - (void)reportScanResult:(NSString *)result
  {
      [self stopReading];
      if (!_lastResult) {
          return;
      }
      _lastResut = NO;
      UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"二维码扫描"
                                                      message:result
                                                     delegate:nil
                                            cancelButtonTitle:@"取消"
                                            otherButtonTitles: nil];
      [alert show];
      // 以下处理了结果，继续下次扫描
      _lastResult = YES;
  }