参考文档

在实际开发中，最方便的还是直接使用第三方如SYQRCodeViewController 和QRCodeReaderViewController。

ZBar

ZBar和ZXing都可以实现扫描二维码，后者更可以生成二维码，但两者都已停止更新维护，并且iOS 8.0后系统也有了自己的二维码生成的扫描。所以第三方就略显尴尬,事实上原生API也是效率最高的。

#import <ZBarSDK.h>
@interface ViewController ()<ZBarReaderViewDelegate>
{
    ZBarReaderView *readerView;
}
@end

//当然先要获得获得授权并判断相机是否可用
- (IBAction)gogoAction:(UIButton *)sender {
    
    //初始化照相机窗口
    readerView = [[ZBarReaderView alloc]init];
    //设置代理
    readerView.readerDelegate = self;
    //自定义大小
    //readerView.frame = CGRectMake(100, 100, 300, 300);
    //设置扫描区域，标准坐标。
    //如果要在readerView上添加控件最好再自定义一个透明view
    readerView.frame=self.view.bounds;
    self.readerView.scanCrop= CGRectMake(0.25,0.3,0.5,0.5）
   
    readerView.center = self.view.center;
    readerview.backgroundColor = [UIColor clearColor];
    readerview.torchMode = NO；//关闭闪光灯
    readerView.allowsPinchZoom = YES;//允许手势变焦
     readerViewshowsFPS = YES;//显示帧率

    //添加到父视图
    [self.view addSubview:readerView];
    //二维码/条形码识别设置
    ZBarImageScanner *scanner = reader.scanner;
    [scanner setSymbology:ZBAR_I25
                   config:ZBAR_CFG_ENABLE
                       to:0];
    //必须启动
    [ readerView start];
  }

/*********ZBarReaderViewDelegate***********/
//扫描开始
-(void)readerViewDidStart:(ZBarReaderView *)readerView{
     readerView.hidden = NO;
}
//扫描停止
- (void) readerView: (ZBarReaderView*) readerView didStopWithError: (NSError*) error{
     readerView.hidden = YES;
}
//扫描到二维码
- (void) readerView: (ZBarReaderView*) readerView  didReadSymbols: (ZBarSymbolSet*) symbols  fromImage: (UIImage*) image{

    //对扫描到的二维码进行解析
    ZBarSymbol *symbol = nil;
     for (symbol in symbols) {
        break;
     }
    NSString *text = symbol.data;
    NSLog(@"%@",text);
    
    //不停止的话会连续扫描
    [readerView stop];
}

AVFoundation

1. 导入库文件
   AVFoundatio.framework CoreImage.framework
2. 代码示例

#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>
#import <CoreImage/CoreImage.h>

@interface ViewController()<AVCaptureMetadataOutputObjectsDelegate>
//捕获会话
@property (nonatomic,strong) AVCaptureSession *session;
//预览图层，可以通过输出设备展示被捕获的数据流。
@property (nonatomic,strong) AVCaptureVideoPreviewLayer *previewLayer;
@end

@implementation ViewController
- (IBAction)scanAction:(UIButton *)sender {
    //实例化拍摄设备
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    //设置输出设备
    NSError *error = nil;
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
    if (error)      return;//没有照相机
   
    //实例化拍摄元数据输出
    AVCaptureMetadataOutput *output=[[AVCaptureMetadataOutput alloc]init];
    //设置输出数据代理
    [output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    
    //实例化拍摄会话
    AVCaptureSession *session =[[AVCaptureSession alloc]init];
    [session setSessionPreset:AVCaptureSessionPresetHigh];//预设输出质量
    //添加会话输入
    [session addInput:input];
    //添加会话输出
    [session addOutput:output];
    //添加会话输出条码类型
    [output setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];
    self.session = session;
    
    //实例化预览图层
    AVCaptureVideoPreviewLayer *preview = [AVCaptureVideoPreviewLayer layerWithSession:_session];
    preview.videoGravity = AVLayerVideoGravityResizeAspectFill;
    //preview.frame = CGRectMake(0, 0, 300, 300);
    preview.frame = [UIScreen mainScreen].bounds;
    //将图层插入当前视图
    [self.view.layer insertSublayer:preview atIndex:100];
    self.previewLayer = preview;
    
    //启动会话
    [_session startRunning];
  }

 //AVCaptureMetadataOutputObjectsDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{
    // 会频繁的扫描，调用代理方法
    // 1. 如果扫描完成，停止会话
    [self.session stopRunning];
    // 2. 删除预览图层
    [self.previewLayer removeFromSuperlayer];
    // 3. 设置界面显示扫描结果
    //判断是否有数据
    NSString *str = nil;
    if (metadataObjects.count > 0) {
        AVMetadataMachineReadableCodeObject *obj = metadataObjects[0];
        //如果需要对url或者名片等信息进行扫描，可以在此进行扩展
        str  = obj.stringValue;
        NSLog(@"%@",str);
    }
    //结束扫描
    [self dismissViewControllerAnimated:NO
                             completion:^{
        UIAlertController *alert = [UIAlertController alertControllerWithTitle:nil message:str preferredStyle:UIAlertControllerStyleAlert];
        UIAlertAction *action = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:nil];
        [alert addAction:action];
        [self presentViewController:alert animated:YES completion:nil];
    }];
}