NSError *error;
AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:&error];
if (error)
{
NSLog(@"%@", [error domain]);
return;
}
self.captureSession = [[AVCaptureSession alloc] init];
[self.captureSession addInput:input];
AVCaptureMetadataOutput *captureMetadataOutput = [[AVCaptureMetadataOutput alloc] init];
[self.captureSession addOutput:captureMetadataOutput];
[captureMetadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[captureMetadataOutput setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];
AVCaptureVideoPreviewLayer *layer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.captureSession];
[layer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
[layer setFrame:self.view.layer.bounds];
[self.view.layer addSublayer:layer];
self.videoPreviewLayer = layer;
[self.captureSession startRunning];
一切顺利，扫描的效率很高。
可出现了一个问题，我只想在屏幕中的小框内扫描，而不是整个屏幕都可以扫描，类似于微信的效果。
查看文档后发现AVCaptureMetadataOutput类有一个属性rectOfInterest。
rectOfInterest的默认值是CGRectMake(0,0,1,1)
0和1是相对于屏幕的比例，而不是具体的数值。
而且x和y，width和height的位置都互换了。
添加代码：
CGRect lensRect = self.lensView.frame;
CGFloat screenW = ScreenSize.width;
CGFloat screenH = ScreenSize.height;
CGRect rectInterest = CGRectMake(CGRectGetMinY(lensRect) / screenH,
((screenW-CGRectGetWidth(lensRect)))/2/screenW,
CGRectGetHeight(lensRect) / screenH,
CGRectGetWidth(lensRect) / screenW);
[captureMetadataOutput setRectOfInterest:rectInterest];
大功告成！
