使用 AVCaptureSession 处理简单照片：收到错误“没有活动且已启用的视频连接”

Question

我开始使用 Xcode 和 swift 用我的 iPhone 拍摄简单的照片。我将几个示例项目归结为下面一个简单的类，该类派生自 AVCapturePhotoCaptureDelegate，具有 Initialize、TakePhoto 方法和回调 photoOutput——即非常简单。为了测试，我创建了一个带有“初始化”和“拍照”按钮的简单应用程序。

当我拍照并调用“photoOutput.capturePhoto”时，它会停止并出现异常“没有活动且已启用的视频连接。”

显然我在归结中错过了一些基本的东西。我从示例项目中遗漏的一件事是预览层...这是否需要活动预览才能运行？这就是缺少“视频”连接的意思吗？为什么会这样要求？

或者我还遗漏了什么？

非常感谢。

import UIKit
import AVFoundation

class cPhotoCaptureNormal: NSObject, AVCapturePhotoCaptureDelegate
{
    private let photoOutput = AVCapturePhotoOutput()
    
    public func Initialize()
    {
        
        let captureSession = AVCaptureSession()
        
        if let captureDevice = AVCaptureDevice.default(for: AVMediaType.video) {
            do {
                let input = try AVCaptureDeviceInput(device: captureDevice)
                if captureSession.canAddInput(input) {
                    captureSession.addInput(input)
                }
            } catch let error {
                print("Failed to set input device with error: \(error)")
            }
            
            if captureSession.canAddOutput(photoOutput) {
                captureSession.addOutput(photoOutput)
            }
            else
            {
                print("Failed to add output device")
            }

            captureSession.startRunning()
        }
    }
    
    public func TakePhoto()
    {
        let photoSettings = AVCapturePhotoSettings()
        if let photoPreviewType = photoSettings.availablePreviewPhotoPixelFormatTypes.first {
            photoSettings.previewPhotoFormat = [kCVPixelBufferPixelFormatTypeKey as String: photoPreviewType]
// EXCEPTION OCCURS ON FOLLOwING LINE
            photoOutput.capturePhoto(with: photoSettings, delegate: self)
        }
    }
    
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {
        guard let imageData = photo.fileDataRepresentation() else { return }
        let previewImage = UIImage(data: imageData)
        
        // ... post process and save UIImage
        

    }
}

Answer 1

假设您在调用

Initialize()

之前调用

TakePhoto()

函数，最有可能导致问题的原因是您的

AVCaptureSession

在

Initialize

结束时超出范围。将

captureSession

设为属性而不是局部变量。这将使会话保持活跃并允许您拍照。

您还应该在某个时候致电

captureSession.stopRunning()

。

class cPhotoCaptureNormal: NSObject, AVCapturePhotoCaptureDelegate {
    private let photoOutput = AVCapturePhotoOutput()
    private let captureSession = AVCaptureSession()
            
    public func initialize() {
        if let captureDevice = AVCaptureDevice.default(for: AVMediaType.video) {
            do {
                let input = try AVCaptureDeviceInput(device: captureDevice)
                if captureSession.canAddInput(input) {
                    captureSession.addInput(input)
                }
            } catch let error {
                print("Failed to set input device with error: \(error)")
            }
            
            if captureSession.canAddOutput(photoOutput) {
                captureSession.addOutput(photoOutput)
            } else {
                print("Failed to add output device")
            }

            captureSession.startRunning()
        }
    }
    
    public func takePhoto() {
        let photoSettings = AVCapturePhotoSettings()
        if let photoPreviewType = photoSettings.availablePreviewPhotoPixelFormatTypes.first {
            photoSettings.previewPhotoFormat = [kCVPixelBufferPixelFormatTypeKey as String: photoPreviewType]
            photoOutput.capturePhoto(with: photoSettings, delegate: self)
        }
    }
    
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {
        guard let imageData = photo.fileDataRepresentation() else { return }
        let previewImage = UIImage(data: imageData)
        
        // ... post process and save UIImage
    }
}

---

在一个不相关的注释中，Swift 中的标准做法是以小写字母开头的函数名称。只有类、结构和枚举名称以大写字母开头。