下载图像后,我创建了一个函数,返回图像的垂直值。
但是,图像的垂直值将失败,并返回CGFloat值。
此源代码将下载并返回。

extension HomeViewController : PinterestLayoutDelegate
{
    func collectionView(_ collectionView: UICollectionView, heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat
    {
        let arts = self.artList

        let model = arts![indexPath.row]

        let urlString = model.url!
        let urll = NSURL(string: urlString)

        return downloadImage(from: urll! as URL)
    }
}

extension HomeViewController
{
    func getData(from url: URL, completion: @escaping (Data?, URLResponse?, Error?) -> ())
    {
        URLSession.shared.dataTask(with: url, completionHandler: completion).resume()
    }

    func downloadImage(from url: URL) -> CGFloat
    {
        getData(from: url)
        { data, response, error in
        guard let data = data, error == nil else { return }
            {
                let image = UIImage(data: data)
                let heightInPoints = image!.size.height
                return heightInPoints
            }
        }
    }
}

但我有个错误
return heightInPoints

错误状态
void函数中意外的非void返回值
请帮帮我。

最佳答案

问题是你想在一个完成块中返回一个值,你需要

func downloadImage(from url: URL,completion(_ value:CGFloat) -> Void )
{
    getData(from: url)
    { data, response, error in
    guard let data = data, error == nil else { return }
        {
            let image = UIImage(data: data)
            let heightInPoints = image!.size.height
            completion(heightInPoints)
        }
    }
}

顺便说一句,你不能这样做
return downloadImage(from: urll! as URL)

由于downloadImage是异步方法,它的响应依赖于网络状态,而不是代码中的串行状态,所以它的调用看起来像
// array of heights
var arr = [CGFloat]()
let urll = URL(string: urlString)
downloadImage(from: urll!) { (value) in
  print(value)
  // append the value to it's corresponding index in an array of floats
  DispatchQueue.main.async {
    self.collectionview.reloadData()
  }
}

如果可能的话,您需要有一个预定义的图像高度列表,如果不可能,则获取所有高度,然后刷新集合

09-10 04:11
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