返回函数内部无效 [英] Void Inside of Return function

问题描述

我正在尝试创建一个用于点击图片的自定义类。在里面，我想创建一个 clickPicture 函数，它返回一个 UIImage 。但是， captureStillImageAsynchronously 是一个 void 。我怎样才能返回我从那里收到的图像？谢谢。

  func clickPicture（） - > UIImage的？如果让videoConnection = stillImageOutput？.connection（withMediaType：AVMediaTypeVideo）{
 
 videoConnection.videoOrientation = .portrait 
 stillImageOutput？.captureStillImageAsynchronously（from：videoConnection， completionHandler：{（sampleBuffer，error） - >无效
 
如果sampleBuffer！= nil {
 
 let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation（sampleBuffer）
 let dataProvider = CGDataProvider（data：imageData！）
 let cgImageRef = CGImage（jpegDataProviderSource：dataProvider !, decode：nil，shouldInterpolate：true，intent：.defaultIntent）
 $ b $ image image = UIImage（cgImage： cgImageRef !, scale：1，orientation：.right）
 
 return image //在void函数中出现意外的非void返回值
 
} 
 return nil //无效
 
中意外的非void返回值}）
 
} 
 
 return nil 
} 
  

中的意外的nil发现后，这是未受挑战的＃2 Swift问题。

这个方法描述得非常好：
$ b

捕捉静止图像异步。

您不能从包含异步任务的方法返回任何内容。

你需要一个完成块：

  func clickPicture（完成：（UIImage？） - > Void）{
 
 guard让videoConnection = stillImageOutput？.connection（withMediaType：AVMediaTypeVideo）else {completion（nil）} 
 
 videoConnection.videoOrientation = .portrait 
 stillImageOutput？.captureStillImageAsynchronously（from：videoConnection ，completionHandler：{（sampleBuffer，error） - > void in 
 
 guard let buffer = sampleBuffer else {completion（nil）} 
 
 let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation（buffer ）
 let dataProvider = CGDataProvider（data：imageData！）
 let cgImageRef = CG Image（jpegDataProviderSource：dataProvider !, decode：nil，shouldInterpolate：true，intent：.defaultIntent）
 
 let image = UIImage（cgImage：cgImageRef !, scale：1，orientation：.right）
 
完成（图片）
 
}）
} 
  

然后调用它：

  clickPicture {image in 
 if unwrappedImage = image {
 //用unwrappedImage做一些事情
} 
} 
  

I am trying to create a custom class for clicking pictures. Inside of it, I would like to create a clickPicture function that returns a UIImage. However, the captureStillImageAsynchronously is a void. How can I return the image I receive from that? Thanks.

func clickPicture() -> UIImage? {

    if let videoConnection = stillImageOutput?.connection(withMediaType: AVMediaTypeVideo) {

        videoConnection.videoOrientation = .portrait
        stillImageOutput?.captureStillImageAsynchronously(from: videoConnection, completionHandler: { (sampleBuffer, error) -> Void in

            if sampleBuffer != nil {

                let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(sampleBuffer)
                let dataProvider = CGDataProvider(data: imageData!)
                let cgImageRef = CGImage(jpegDataProviderSource: dataProvider!, decode: nil, shouldInterpolate: true, intent: .defaultIntent)

                let image = UIImage(cgImage: cgImageRef!, scale: 1, orientation: .right)

                return image //Unexpected non-void return value in void function

            }
            return nil //Unexpected non-void return value in void

        })

    }

    return nil
}

解决方案

That's the unchallenged #2 Swift question after unexpected nil found while unwrapping an optional.

The method describes pretty well what is does :

capture still image asynchronously.

You cannot return anything from a method which contains an asynchronous task.
You need a completion block:

func clickPicture(completion:(UIImage?) -> Void) {

    guard let videoConnection = stillImageOutput?.connection(withMediaType: AVMediaTypeVideo)  else { completion(nil) }

    videoConnection.videoOrientation = .portrait
    stillImageOutput?.captureStillImageAsynchronously(from: videoConnection, completionHandler: { (sampleBuffer, error) -> Void in

        guard let buffer = sampleBuffer else { completion(nil) }

        let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(buffer)
        let dataProvider = CGDataProvider(data: imageData!)
        let cgImageRef = CGImage(jpegDataProviderSource: dataProvider!, decode: nil, shouldInterpolate: true, intent: .defaultIntent)

        let image = UIImage(cgImage: cgImageRef!, scale: 1, orientation: .right)

        completion(image) 

    })
}

and call it this way:

clickPicture { image in 
   if unwrappedImage = image {
     // do something with unwrappedImage
   } 
}

这篇关于返回函数内部无效的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！