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现如今几乎每个app基本都有扫描功能，提高了用户体验。所以掌握这项技能必不可少。

在开始写代码之前，我们需要先导入扫描二维码的框架<AVFoundation/AVFoundation.h>

//需要实现扫描二维码的代理方法 @interface ViewController ()
   
    //在stotyboard中添加一个扫描的视图和开始or暂停的按钮@property (weak, nonatomic) IBOutlet UIView *scanView;@property (weak, nonatomic) IBOutlet UIButton *button;@property (nonatomic ,strong) AVCaptureSession *captureSession;@property (nonatomic ,strong) AVCaptureVideoPreviewLayer *captureVideoPreviewLayer;@end
   

屏幕快照 2016-04-08 下午4.28.01.png

-(BOOL)startScanning{    [_button setTitle:@"stop" forState:UIControlStateNormal];    NSError *error = nil;    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];    //添加线程    dispatch_queue_t dispatchQueue;    dispatchQueue = dispatch_queue_create("ScanQRCodeQueue", NULL);    //设置代理方法    [captureMetadataOutput setMetadataObjectsDelegate:self queue:dispatchQueue];    [captureMetadataOutput setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];    //创建扫描view的layer层    _captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc]initWithSession:_captureSession];    //将图层设置为视频样式    [_captureVideoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];    //设置layer的位置    [_captureVideoPreviewLayer setFrame:_scanView.frame];    [self.view.layer addSublayer:_captureVideoPreviewLayer];    //开始扫描    [_captureSession startRunning];    return YES;}

停止扫描的方法

-(void)stopScanning{    //停止扫描    [_captureSession stopRunning];    //将会话置为nil    _captureSession = nil;    //将button切换回去    [_button setTitle:@"start" forState:UIControlStateNormal];}

扫描的代理方法，接收扫描结果

#pragma mark-----代理方法-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{    //判断扫描是否有数据    if (metadataObjects != nil && [metadataObjects count] > 0) {        AVMetadataMachineReadableCodeObject *metadataObject = [metadataObjects objectAtIndex:0];        NSString *result;         //判断的扫描的结果是否是二维码        if ([[metadataObject type] isEqualToString:AVMetadataObjectTypeQRCode]) {            result = metadataObject.stringValue;        }else{            NSLog(@"不是二维码");        }        //返回主线程，并将扫描的结果传回主线程        [self performSelectorOnMainThread:@selector(reportScanResult:) withObject:result waitUntilDone:NO];    }}-(void)reportScanResult:(NSString *)result{    //扫描完毕，停止扫描    [self stopScanning];    //创建对话框，将扫描结果以对话框的形式呈现    UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"提示" message:result preferredStyle:UIAlertControllerStyleAlert];    UIAlertAction *action = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {    }];    [alert addAction:action];    [self presentViewController:alert animated:YES completion:nil];}

- (IBAction)startScan:(UIButton *)sender {    //点击按钮的时候判断是否是没有在扫描状态，是则开始，不是就暂停    if ([sender.titleLabel.text isEqualToString:@"start"]) {        [self startScanning];    }else{        [self stopScanning];    }}

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