之前总觉得二维码扫描很高大上，其实apple工程师早就为我们提供了便捷的方法。二维码扫描第三方的库也挺多的，不过效率高的当属系统提供的扫描方法。
二维码扫描主要用到了以下几个类：AVCaptureDevice,AVCaptureDeviceInput,AVCaptureMetadataOutput,AVCaptureSession,AVCaptureVideoPreviewLayer
它们之间的关系看这篇文章
扫描的核心代码如下：（最后附上完整代码）
//获取摄像设备AVCaptureDevice * device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];if (!device) return;//创建输入流AVCaptureDeviceInput * input = [AVCaptureDeviceInput deviceInputWithDevice:device error:nil];if (!input) return;//创建输出流AVCaptureMetadataOutput * output = [[AVCaptureMetadataOutput alloc]init];if (!output) return;output.rectOfInterest = CGRectMake(0.1, 0, 0.9, 1);//设置代理 在主线程里刷新[output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];//初始化链接对象_session = [[AVCaptureSession alloc]init];//高质量采集率[_session setSessionPreset:AVCaptureSessionPresetHigh];if ([_session canAddInput:input]) {[_session addInput:input];}else{return;}if ([_session canAddOutput:output]) {[_session addOutput:output];}else{return;}//设置扫码支持的编码格式(如下设置条形码和二维码兼容)output.metadataObjectTypes=@[AVMetadataObjectTypeQRCode,AVMetadataObjectTypeEAN13Code, AVMetadataObjectTypeEAN8Code, AVMetadataObjectTypeCode128Code];AVCaptureVideoPreviewLayer * layer = [AVCaptureVideoPreviewLayer layerWithSession:_session];layer.videoGravity = AVLayerVideoGravityResizeAspectFill;layer.frame = self.view.layer.bounds;[self.view.layer insertSublayer:layer atIndex:0];//开始捕获[_session startRunning];完整代码地址
