无法将类型“(_) -> ()”的值转换为预期的参数类型“((Bool, Error?) -> Void)？”

Question

拜托，我需要帮助解决问题，我将语法 Swift 3 更改为 swift 4，现在我在识别所有 bugs.The 错误时遇到很多问题最后一行的 savePhoto 函数，completionHandler: { _ in

func takePhoto(_ previewLayer: AVCaptureVideoPreviewLayer, location: CLLocation?, completion: (() -> Void)? = nil) {
    guard let connection = stillImageOutput?.connection(with: AVMediaType.video) else { return }

    connection.videoOrientation = Helper.videoOrientation()

    queue.async {
      self.stillImageOutput?.captureStillImageAsynchronously(from: connection) {
        buffer, error in

        guard let buffer = buffer, error == nil && CMSampleBufferIsValid(buffer),
          let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(buffer),
          let image = UIImage(data: imageData)
          else {
            DispatchQueue.main.async {
              completion?()
            }
            return
        }

        self.savePhoto(image, location: location, completion: completion)
      }
    }
  }

  func savePhoto(_ image: UIImage, location: CLLocation?, completion: (() -> Void)? = nil) {
    PHPhotoLibrary.shared().performChanges({
      let request = PHAssetChangeRequest.creationRequestForAsset(from: image)
      request.creationDate = Date()
      request.location = location
    }, completionHandler: { _ in
        DispatchQueue.main.async {
          completion?()
        }
    })
  }

Answer 1

改写为：

}, completionHandler: { (_, _) in

根据 documentation，performChanges(_:completionHandler:) 中的完成处理程序接受两个参数，而不仅仅是一个。 _ in，你用的，只是一个单一参数的占位符。

Answer 2

正如您在错误消息中清楚看到的那样，completionHandler 传递了两个参数，而不是一个。

所以你必须写

}, completionHandler: { (_, _) in

但强烈建议您处理结果和潜在的错误。忽略错误会导致糟糕的用户体验。

无法将类型“(_) -> ()”的值转换为预期的参数类型“((Bool, Error?) -> Void)？”

Cannot convert value of type '(_) -> ()' to expected argument type '((Bool, Error?) -> Void)?'

ios

iphone

swift

swift3

ios9