一、扫描二维码需要4个对象

// 1.输入设备 
@property (nonatomic, strong) AVCaptureDeviceInput *deviceInput;
// 2.输出设备   metadata 元数据
@property (nonatomic, strong) AVCaptureMetadataOutput *metadataOutput;
// 3.会话  连接输入和输出设备
@property (nonatomic, strong) AVCaptureSession *session;
// 4.预览界面  预览摄像头采集到的信息   -->特殊的图层
@property (nonatomic, strong) AVCaptureVideoPreviewLayer *previewLayer;

二、实例化 并配置 各对象

    // 1.输入设备  -->键盘  摄像头  麦克风
    // 默认是后置摄像头
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    self.deviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:device error:nil];
    // 2.输出设备  -->解析数据
    self.metadataOutput = [[AVCaptureMetadataOutput alloc] init];
    // 设置输出设备代理 在扫描到信息时可执行回调
    [self.metadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    // 3.会话 -->连接输入和输出设备
    self.session = [[AVCaptureSession alloc] init];
    if ([self.session canAddInput:self.deviceInput]) {
        [self.session addInput:self.deviceInput];
    }
    if ([self.session canAddOutput:self.metadataOutput]) {
        [self.session addOutput:self.metadataOutput];
    }
    // 设置需要解析的数据类型
    self.metadataOutput.metadataObjectTypes = @[AVMetadataObjectTypeQRCode];
    // 4.预览界面  -->预览摄像头采集到的信息   -->特殊的图层
    self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session];
    self.previewLayer.frame = self.view.bounds;
    [self.view.layer addSublayer:self.previewLayer];
    // 5.开启会话
    [self.session startRunning];

三、扫描到信息时的回调,如果不主动取消,会一直调用.

#pragma mark - AVCaptureMetadataOutputObjectsDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{
    
    //关闭会话
    [self.session stopRunning];
    [self.previewLayer removeFromSuperlayer];  
    [self dismissViewControllerAnimated:YES completion:nil];

    //使用Safari 控制器 加载页面
    if ([[metadataObjects.firstObject stringValue] hasPrefix:@"http"]||[[metadataObjects.firstObject stringValue] hasPrefix:@"https"]) {
        SFSafariViewController *safarVC = [[SFSafariViewController alloc]initWithURL:[NSURL URLWithString:[metadataObjects.firstObject stringValue]]];
        [self presentViewController:safarVC animated:YES completion:nil];
        
    }
   
//使用 block 进行数据逆传
        self.complete([metadataObjects.firstObject stringValue]);   
}

四、可以自定义一个 view 完成 UI 页面设置
有两个地方需要注意:

需要改变 view 的 layer -->AVCaptureVideoPreviewLayer
需要将会话 session 传给 view

#import "NEQRPreview.h"

@interface NEQRPreview ()
@property (nonatomic, strong) UIImageView *imageView;
@property (nonatomic, strong) UIImageView *lineImageView;
@property (nonatomic, strong) NSTimer *timer;

@end

@implementation NEQRPreview
//给 session 赋值
- (void)setSession:(AVCaptureSession *)session{
    _session = session;
    AVCaptureVideoPreviewLayer *layer = (AVCaptureVideoPreviewLayer *) self.layer;
    layer.session = session;

}
//改变 View layer
+(Class)layerClass{
    return [AVCaptureVideoPreviewLayer class];
}

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self initUiConfig];
    }
    return self;
}

//在一个视图中设置二维码UI的垃圾代码
- (void)initUiConfig
{
    //设置背景图片
    _imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"pick_bg.png"]];
    //设置位置到界面的中间
    _imageView.frame = CGRectMake(self.bounds.size.width * 0.5 - 140, self.bounds.size.height * 0.5 - 140, 280, 280);
    
    NSLog(@"%@",NSStringFromCGRect( _imageView.frame));
    
    //添加到视图上
    [self addSubview:_imageView];
    
    //初始化二维码的扫描线的位置
    _lineImageView = [[UIImageView alloc] initWithFrame:CGRectMake(30, 10, 220, 2)];
    _lineImageView.image = [UIImage imageNamed:@"line.png"];
    [_imageView addSubview:_lineImageView];
    
    //开启定时器
    _timer = [NSTimer scheduledTimerWithTimeInterval:3 target:self selector:@selector(animation) userInfo:nil repeats:YES];
}

- (void)animation
{
    [UIView animateWithDuration:2.8 delay:0 options:UIViewAnimationOptionCurveLinear animations:^{
        
        _lineImageView.frame = CGRectMake(30, 260, 220, 2);
        
    } completion:^(BOOL finished) {
        _lineImageView.frame = CGRectMake(30, 10, 220, 2);
    }];
}

@end

注意:

如出现以下提示

This app has crashed because it attempted to access privacy-sensitive data without a usage description. The app's Info.plist must contain an NSCameraUsageDescription key with a string value explaining to the user how the app uses this data.

解决方法 :

在 Info.plist中加入 NSCameraUsageDescription 字段即可.

DEMO：GitHub