iOS关于ZXing扫码在控制器dissmiss导致崩溃的问题

最近因为项目中有扫码登录的需求，一开始用的是系统的AVFoundation库实现的扫码功能

@property (nonatomic,strong) AVCaptureSession *captureSession;//捕捉会话

@property (nonatomic,strong) AVCaptureDeviceInput *deviceInput;//输入流

@property (nonatomic,strong) AVCaptureMetadataOutput *metaDataOutput;//输出流

@property (nonatomic,strong) AVCaptureVideoPreviewLayer *videoPreviewLayer;//预览图层

//开始扫描
- (void)startCapture{
    if (![self requestDeviceAuthorization]) {
        [[UUCommon shareInstance] uu_alertWithTitle:@"没有相机访问权限" message:@"请在设置->通用->相机中允许访问" centerStr:@"去设置" centerItem:^{
            NSURL *url = [[NSURL alloc] initWithString:UIApplicationOpenSettingsURLString];// 跳转至系统设置
            [[UIApplication sharedApplication] openURL:url];
        }];
        return;
    }
    
    [self.captureSession beginConfiguration];
    if ([self.captureSession canAddInput:self.deviceInput]) {
        [self.captureSession addInput:self.deviceInput];
    }
    // 设置数据输出类型，需要将数据输出添加到会话后，才能指定元数据类型，否则会报错
    if ([self.captureSession canAddOutput:self.metaDataOutput]) {
        [self.captureSession addOutput:self.metaDataOutput];
        //设置扫码支持的编码格式(如下设置条形码和二维码兼容)
        NSArray *types = @[AVMetadataObjectTypeQRCode,AVMetadataObjectTypeEAN13Code, AVMetadataObjectTypeEAN8Code, AVMetadataObjectTypeCode128Code,AVMetadataObjectTypeCode93Code];
        self.metaDataOutput.metadataObjectTypes =types;
    }
    [self.captureSession commitConfiguration];
    [self.captureSession startRunning];
}

//停止扫描
- (void)stopCapture{
    [self.captureSession stopRunning];
    [self.shadowView uu_scanStop];
}

#pragma mark - 请求权限
- (BOOL)requestDeviceAuthorization{
    
    AVAuthorizationStatus deviceStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
    if (deviceStatus == AVAuthorizationStatusRestricted ||
        deviceStatus ==AVAuthorizationStatusDenied){
        return NO;
    }
    return YES;
}

#pragma mark - AVCaptureMetadataOutputObjectsDelegate
- (void)captureOutput:(AVCaptureOutput *)output didOutputMetadataObjects:(NSArray<__kindof AVMetadataObject *> *)metadataObjects fromConnection:(AVCaptureConnection *)connection{
    //获取到扫描的数据
    AVMetadataMachineReadableCodeObject *dateObject = (AVMetadataMachineReadableCodeObject *) [metadataObjects lastObject];
    [self.captureSession stopRunning];
    NSLog("%@", dateObject.stringValue);
}

后来参考一下第三方的ZXing库，可以解决系统扫码识别乱码问题，主要是和安卓端保持一致，就开始修改成ZXing的扫码：

//导入头文件
#import <ZXingObjC/ZXingObjC.h>
//遵循代理<ZXCaptureDelegate>
//ZXCapture捕获器
@property (nonatomic, strong) ZXCapture *capture;             //ZXCapture捕获器

//加载ZXCapture捕获器
- (void)setupCapture {
self.capture = [[ZXCapture alloc] init];
    self.capture.camera = self.capture.back;
    //自动聚焦
    self.capture.focusMode = AVCaptureFocusModeContinuousAutoFocus;
    [self.view.layer addSublayer:self.capture.layer];
    self.capture.delegate = self;
}

//开始扫描
- (void)startCapture {
    if (![self requestDeviceAuthorization]) {
        [self alertWithTitle:@"没有相机权限" message:@"请在设置-通用-相机-允许访问" leftStr:@"去设置" rightStr:@"取消" leftItem:^{
            NSURL *openURL = [NSURL URLWithString:UIApplicationOpenSettingsURLString];
            [[UIApplication sharedApplication] openURL:openURL];
        } rightItem:^{
            
        }];
        
        return;
    }
    
    //TODO:ZXing捕获器
    [self.capture start];
}

//停止扫描
- (void)stopCapture {
    //TODO:ZXing停止扫码
    [self.capture stop];
}

#pragma mark - ZXCaptureDelegate
- (void)captureResult:(ZXCapture *)capture result:(ZXResult *)result {
    if (!result) return;
    
    if (self.capture.layer.superlayer) {
        if (result.barcodeFormat == kBarcodeFormatQRCode) {
            AudioServicesPlaySystemSound(kSystemSoundID_Vibrate);
            
            [self stopCapture];
            
            NSLog(@"识别的二维码的内容 = %@", result.text);
        }
    }
}

这就完了？等等，扫码的功能是实现了，本例中用到的是模态出的扫描二维码页面，dismiss的时候在iOS13的机型上会闪退。通过百度大法后才知道ZXing库需要在控制器dismiss的前移除layer，不然会导致崩溃。

修复的代码：
self.capture.delegate = nil;
[self.capture.layer removeFromSuperlayer];