iOS：原生二维码扫描

　　做iOS的二维码扫描，有两个第三方库可以选择，ZBar和ZXing。今天要介绍的是iOS7.0后AVFoundation框架提供的原生二维码扫描。

首先需要添加AVFoundation.framework框架到你工程中build phase的"Link Binary With Libraries"之下，然后就可以开始了。

　　一、做好准备工作，搭建UI

　　UI效果如图

　　IBOutlet、IBAction如下：

@property (weak, nonatomic) IBOutlet UIView *viewPreview;
@property (weak, nonatomic) IBOutlet UILabel *lblStatus;
@property (weak, nonatomic) IBOutlet UIButton *startBtn;
- (IBAction)startStopReading:(id)sender;

　　接下来就都是代码的事情了

　　二、控制器ViewController.h

　　首先导入AVFoundation框架

#import <AVFoundation/AVFoundation.h>

　　然后控制器实现AVCaptureMetadataOutputObjectsDelegate协议

@interface ViewController ()<AVCaptureMetadataOutputObjectsDelegate>

　　整体property如下：

@property (strong, nonatomic) UIView *boxView;
@property (nonatomic) BOOL isReading;
@property (strong, nonatomic) CALayer *scanLayer;

-(BOOL)startReading;
-(void)stopReading;

//捕捉会话
@property (nonatomic, strong) AVCaptureSession *captureSession;
//展示layer
@property (nonatomic, strong) AVCaptureVideoPreviewLayer *videoPreviewLayer;

　　然后在ViewDidLoad方法中初始化

- (void)viewDidLoad {
    [super viewDidLoad];

    _captureSession = nil;
     _isReading = NO;
    
}

　　接下来实现startReading方法（这可就是重点咯）

- (BOOL)startReading {
    NSError *error;
    
    //1.初始化捕捉设备（AVCaptureDevice），类型为AVMediaTypeVideo
    AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    
    //2.用captureDevice创建输入流
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:&error];
    if (!input) {
        NSLog(@"%@", [error localizedDescription]);
        return NO;
    }
    
    //3.创建媒体数据输出流
    AVCaptureMetadataOutput *captureMetadataOutput = [[AVCaptureMetadataOutput alloc] init];
    
    //4.实例化捕捉会话
    _captureSession = [[AVCaptureSession alloc] init];
    
    //4.1.将输入流添加到会话
    [_captureSession addInput:input];
    
    //4.2.将媒体输出流添加到会话中
    [_captureSession addOutput:captureMetadataOutput];
    
    //5.创建串行队列，并加媒体输出流添加到队列当中
    dispatch_queue_t dispatchQueue;
    dispatchQueue = dispatch_queue_create("myQueue", NULL);
    //5.1.设置代理
    [captureMetadataOutput setMetadataObjectsDelegate:self queue:dispatchQueue];
    
    //5.2.设置输出媒体数据类型为QRCode
    [captureMetadataOutput setMetadataObjectTypes:[NSArray arrayWithObject:AVMetadataObjectTypeQRCode]];
    
    //6.实例化预览图层
    _videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
    
    //7.设置预览图层填充方式
    [_videoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
    
    //8.设置图层的frame
    [_videoPreviewLayer setFrame:_viewPreview.layer.bounds];
    
    //9.将图层添加到预览view的图层上
    [_viewPreview.layer addSublayer:_videoPreviewLayer];
    
    //10.设置扫描范围
    captureMetadataOutput.rectOfInterest = CGRectMake(0.2f, 0.2f, 0.8f, 0.8f);
    
    //10.1.扫描框
    _boxView = [[UIView alloc] initWithFrame:CGRectMake(_viewPreview.bounds.size.width * 0.2f, _viewPreview.bounds.size.height * 0.2f, _viewPreview.bounds.size.width - _viewPreview.bounds.size.width * 0.4f, _viewPreview.bounds.size.height - _viewPreview.bounds.size.height * 0.4f)];
    _boxView.layer.borderColor = [UIColor greenColor].CGColor;
    _boxView.layer.borderWidth = 1.0f;
    
    [_viewPreview addSubview:_boxView];
    
    //10.2.扫描线
    _scanLayer = [[CALayer alloc] init];
    _scanLayer.frame = CGRectMake(0, 0, _boxView.bounds.size.width, 1);
    _scanLayer.backgroundColor = [UIColor brownColor].CGColor;
    
    [_boxView.layer addSublayer:_scanLayer];
    
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.2f target:self selector:@selector(moveScanLayer:) userInfo:nil repeats:YES];
    [timer fire];

    //10.开始扫描
    [_captureSession startRunning];
    return YES;
}

　　实现AVCaptureMetadataOutputObjectsDelegate协议方法

#pragma mark - AVCaptureMetadataOutputObjectsDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection
{
    //判断是否有数据
    if (metadataObjects != nil && [metadataObjects count] > 0) {
        AVMetadataMachineReadableCodeObject *metadataObj = [metadataObjects objectAtIndex:0];
        //判断回传的数据类型
        if ([[metadataObj type] isEqualToString:AVMetadataObjectTypeQRCode]) {
            [_lblStatus performSelectorOnMainThread:@selector(setText:) withObject:[metadataObj stringValue] waitUntilDone:NO];
            
            [self performSelectorOnMainThread:@selector(stopReading) withObject:nil waitUntilDone:NO];
            _isReading = NO;
        }
    }
}

　　实现计时器方法moveScanLayer:(NSTimer *)timer

- (void)moveScanLayer:(NSTimer *)timer
{
    CGRect frame = _scanLayer.frame;
    if (_boxView.frame.size.height < _scanLayer.frame.origin.y) {
        frame.origin.y = 0;
        _scanLayer.frame = frame;
    }else{
        
        frame.origin.y += 5;
        
        [UIView animateWithDuration:0.1 animations:^{
            _scanLayer.frame = frame;
        }];
    }
}

　　实现开始和停止方法

- (IBAction)startStopReading:(id)sender {
        if (!_isReading) {
            if ([self startReading]) {
                [_startBtn setTitle:@"Stop" forState:UIControlStateNormal];
                [_lblStatus setText:@"Scanning for QR Code"];
            }
        }
        else{
            [self stopReading];
            [_startBtn setTitle:@"Start!" forState:UIControlStateNormal];
        }
        
        _isReading = !_isReading;
}

-(void)stopReading{
    [_captureSession stopRunning];
    _captureSession = nil;
    [_scanLayer removeFromSuperlayer];
    [_videoPreviewLayer removeFromSuperlayer];
}

　　大功告成

　　示例源码地址：https://github.com/WuKongCoo1/QRCodeReader