首相介绍相关的类

AVCaptureSession

AVCaptureSession 它是管理捕获活动并协调来自输入设备的数据流以捕获输出的对象。
要执行实时或离线捕获，您需要实例化一个 AVCaptureSession 对象并添加适当的输入（例如 AVCaptureDeviceInput ）和输出（例如 AVCaptureMovieFileOutput ）。 以下代码片段说明了如何配置捕获设备以记录音频：

AVCaptureSession *captureSession = [[AVCaptureSession alloc] init];
AVCaptureDevice *audioCaptureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
NSError *error = nil;
AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioCaptureDevice error:&error];
if (audioInput) {
    [captureSession addInput:audioInput];
}
else {
    // Handle the failure.
}

AVCaptureDevice

为捕获会话提供输入（例如音频或视频）并提供针对硬件特定捕获功能的控制的设备。

// 方法1
// Choose the back dual camera if available, otherwise default to a wide angle camera.
    AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithDeviceType:AVCaptureDeviceTypeBuiltInDuoCamera mediaType:AVMediaTypeVideo position:AVCaptureDevicePositionBack];
    if ( ! videoDevice ) {
        // If the back dual camera is not available, default to the back wide angle camera.
        videoDevice = [AVCaptureDevice defaultDeviceWithDeviceType:AVCaptureDeviceTypeBuiltInWideAngleCamera mediaType:AVMediaTypeVideo position:AVCaptureDevicePositionBack];
        // In some cases where users break their phones, the back wide angle camera is not available. In this case, we should default to the front wide angle camera.
        if ( ! videoDevice ) {
            videoDevice = [AVCaptureDevice defaultDeviceWithDeviceType:AVCaptureDeviceTypeBuiltInWideAngleCamera mediaType:AVMediaTypeVideo position:AVCaptureDevicePositionFront];
        }
    }

// 新方法1
+ (instancetype)discoverySessionWithDeviceTypes:(NSArray<AVCaptureDeviceType> *)deviceTypes mediaType:(NSString *)mediaType position:(AVCaptureDevicePosition)position;

// 方法2
AVCaptureDevice *device = [AVCaptureDevice
                               defaultDeviceWithMediaType:AVMediaTypeVideo];

AVCaptureInput

用于向捕获会话提供输入数据的对象的抽象超类。
要将AVCaptureInput对象与会话关联，请在会话上调用 addInput：。
AVCaptureInput对象具有一个或多个端口（AVCaptureInputPort的实例），它们可以生成每个数据流一个。 例如，呈现一个视频数据流的AVCaptureDevice对象具有一个端口。

AVCaptureDeviceInput

AVCaptureDeviceInput 它是捕获输入类，提供从捕获设备到捕获会话（AVCaptureSession）的媒体。
AVCaptureDeviceInput 是AVCaptureInput 的一个具体子类，用于从AVCaptureDevice 对象捕获数据。

AVCaptureDeviceInput *videoDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    if ( ! videoDeviceInput ) {
        NSLog( @"Could not create video device input: %@", error );
        return;
    }
    if ( [self.session canAddInput:videoDeviceInput] ) {
        [self.session addInput:videoDeviceInput];
    }

AVCaptureOutput

AVCaptureOutput 是描述 AVCaptureSession 对象的输出目标的抽象基类。
AVCaptureOutput提供了一个抽象接口，用于将捕获输出目标（例如文件和视频预览）连接到捕获会话（AVCaptureSession 的实例）。 捕获输出可以具有由AVCaptureConnection 对象表示的多个连接，每个连接对象从捕获输入（AVCaptureInput的实例）接收的每个媒体流。 捕获输出在首次创建时没有任何连接。 将输出添加到捕获会话时，将创建将媒体数据从该会话的输入映射到其输出的连接。
您可以使用addOutput（_ :)将具体的AVCaptureOutput 实例添加到捕获会话。

// 照片输出
AVCapturePhotoOutput *photoOutput = [[AVCapturePhotoOutput alloc] init];
    if ( [self.session canAddOutput:photoOutput] ) {
        [self.session addOutput:photoOutput];
    }
//视频输出
AVCaptureMovieFileOutput *movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
if ( [self.session canAddOutput:movieFileOutput] )
    {
        [self.session beginConfiguration];
        [self.session addOutput:movieFileOutput];
        self.session.sessionPreset = AVCaptureSessionPresetHigh;
        AVCaptureConnection *connection = [movieFileOutput connectionWithMediaType:AVMediaTypeVideo];
        if ( connection.isVideoStabilizationSupported ) {
            connection.preferredVideoStabilizationMode = AVCaptureVideoStabilizationModeAuto;
        }
        [self.session commitConfiguration];
    }
// 元数据
 AVCaptureMetadataOutput *output2 = [[AVCaptureMetadataOutput alloc] init];
    [_session addOutput:output2];
    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
    [output2 setMetadataObjectsDelegate:self queue:queue];

AVCaptureVideoPreviewLayer

核心动画层，可以在捕获视频时显示。
AVCaptureVideoPreviewLayer 是CALayer 的子类，用于在视频被输入设备捕获时用于显示视频。
您可以将此预览图层与AV捕获会话结合使用，如以下代码段所示：

AVCaptureSession *captureSession = <#Get a capture session#>;
AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:captureSession];
UIView *aView = <#The view in which to present the layer#>;
previewLayer.frame = aView.bounds; // Assume you want the preview layer to fill the view.
[aView.layer addSublayer:previewLayer];

二维码扫描

主要代码：

 NSError *error = nil;
    
    // 初始化会话
    _session = [[AVCaptureSession alloc] init];
    
    // 设置会话设置输出质量
    _session.sessionPreset = AVCaptureSessionPresetMedium;
 
    // 获取需要的设备
    AVCaptureDevice *device = [AVCaptureDevice
                               defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
                                                                        error:&error];
    if (!input) {
        // Handling the error appropriately.
    }
    [_session addInput:input];
    
    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
 // 
    AVCaptureMetadataOutput *output2 = [[AVCaptureMetadataOutput alloc] init];
    [_session addOutput:output2];
    [output2 setMetadataObjectsDelegate:self queue:queue];
    
// 设置为二维码类型（AVMetadataObjectTypeQRCode），
// 还有其他类型，可以去接口文件里查看
    [output2 setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];

    // Start the session running to start the flow of data
    [_session startRunning];
    
    //预览层的生成，实时获取摄像头数据
    self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_session];
    self.previewLayer.frame = CGRectMake(0, 64, 300, 304);
    self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    [self.view.layer addSublayer:self.previewLayer];

代理：<AVCaptureMetadataOutputObjectsDelegate>

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
    if (metadataObjects.count > 0) {
        //获得扫描数据，最后一个是最新扫描的数据
        AVMetadataMachineReadableCodeObject *object = [metadataObjects lastObject];
        // 结果  object.stringValue
        dispatch_async(dispatch_get_main_queue(), ^{
            _label.text = object.stringValue;
        });
    } else {
        dispatch_async(dispatch_get_main_queue(), ^{
            _label.text = @"没有扫描到数据";
        });
        
    }
}