iOS 原生扫码

iOS 可以自己识别二维码，完全不用去找第三方文件。
摄像头用AVFoundation来实现：

@property (strong, nonatomic) AVCaptureSession *session;//整个捕捉过程的中心@property (strong, nonatomic) AVCaptureDeviceInput *inputDevice;//输入设备@property (strong, nonatomic) AVCaptureMetadataOutput *metadataOutput;//输出设备@property (strong, nonatomic) AVCaptureVideoPreviewLayer *previewLayer;//预览层

NSError *err = nil;//init session_session = [[AVCaptureSession alloc]init];_session.sessionPreset = AVCaptureSessionPresetHigh;//图像质量，设置的高点，识别的准点//add inputAVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];_inputDevice = [AVCaptureDeviceInput deviceInputWithDevice:device error:&err];if (!err) {  if ([_session canAddInput:_inputDevice]) {     [_session addInput:_inputDevice];  }}else{  NSLog(@"err: %@", err);}//add output，output有多种，包括输出图片、视频文件等。AVCaptureMetadataOutput逐帧向代理发送数据_metadataOutput = [[AVCaptureMetadataOutput alloc]init];[_metadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];/*一般扫码的UI中都有一个maskView，所以应特别注意表示识别范围的属性rectOfInterest:它的四个值的范围都是0-1，表示比例，x对应的恰恰是距离左上角的垂直距离，y对应的是距离左上角的水平距离。*/_metadataOutput.rectOfInterest = CGRectMake(...);if ([_session canAddOutput:_metadataOutput]) {        [_session addOutput:_metadataOutput];}_metadataOutput.metadataObjectTypes = @[AVMetadataObjectTypeQRCode];//要捕捉的数据是二维码//init preview_previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:_session];_previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;_previewLayer.frame = _screenRect;[self.view.layer insertSublayer:_previewLayer atIndex:0];[_session startRunning];

处理二维码的方法在代理中：

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{if ([metadataObjects count] > 0) {//捕捉到了二维码   [_session stopRunning];//关闭摄像头   AVMetadataMachineReadableCodeObject *metadataObject = metadataObjects[0];//得到该二维码对象，然后进行处理   NSString *value = metadataObject.stringValue;//用最粗暴的方式，直接拿了value        NSLog(@"%@", value);    ...}

需要注意的有：

-(void)viewDidDisappear:(BOOL)animated{    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{//如果在主线程上关闭，会崩溃        [_session stopRunning];    });}