如何使用NSCache从UICollectionView中的Web服务器异步加载图像

使用NScache从UICollectionView中的Web服务器加载图像时，我遇到一些问题.

I have some issues when loading images from a web-server in UICollectionView using NScache.

问题:

图像显示不正确:

1. 有时它们未显示在相应的单元格中

或

1. 图像在滚动变化

情况:

1. 我有3个数组，可以从Web服务器的viewDidLoad()函数中正确加载.这些数组是:vPrice，vTitle和vImages_api

1. I have 3 arrays whitch are properly loaded from the web-server in function viewDidLoad(). These arrays are: vPrice, vTitle and vImages_api

我对单元格的自定义类有:

my custom class for cell have:

• 价格标签:cell.lblPrice

• label for price: cell.lblPrice

标题标签:cell.lblTitle

label for title: cell.lblTitle

图片:cell.imgPicture

image: cell.imgPicture

我相信问题出在函数func collectionView(_ collectionView:UICollectionView，cellForItemAt indexPath:IndexPath)-> UICollectionViewCell

I belive that the problem is in function func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell

这可能与我使用NSCache的方式或我使用DispatchQueue的方式有关.

It could be related either to the way I use NSCache or to the way I use and when I use DispatchQueue.

代码:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = self.collectionViewPRODUSE.dequeueReusableCell(withReuseIdentifier: "customCell", for: indexPath) as! clsCustomCell

    cell.lblPrice.text = vPrice[indexPath.item]
    cell.lblTitle.text = vTitle[indexPath.item]

    cell.layer.borderColor = UIColor.lightGray.cgColor
    cell.layer.borderWidth = 0.5

    DispatchQueue.global(qos: .userInitiated).async {
        //background thread
        let ImageString = self.vImages_api[indexPath.item]
        let imageUrl = URL(string: ImageString)
        let imageData = NSData(contentsOf: imageUrl!)

        // main thread to update the UI
        DispatchQueue.main.async {
            let key1 = self.vImages_api[indexPath.item] as AnyObject
            //if i saved allready my image in cache, then i will load my image from cache
            if let imageFromCache = self.objCache.object(forKey: key1){
                cell.imgPicture.image = imageFromCache as! UIImage
            }
            else{//if my image is not in cache  ......
                        if imageData != nil {
                            let myPicture = UIImage(data: imageData! as Data)
                            cell.imgPicture.image = myPicture                 

                            //save my image in cache
                            self.objCache.setObject(myPicture!, forKey: ImageString as AnyObject)
                        }
            }
        }
    }

    return cell
}

编辑后的代码-版本II:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = self.collectionViewPRODUSE.dequeueReusableCell(withReuseIdentifier: "MyCustomCell", for: indexPath) as! clsCustomCell

    cell.lblPret.text = vPrice[indexPath.item]
    cell.lblTitlu.text = vTitle[indexPath.item]

    cell.layer.borderColor = UIColor.lightGray.cgColor
    cell.layer.borderWidth = 0.5
    let key1 = self.vImages_api[indexPath.item] as AnyObject

    if let imageFromCache = self.objCache.object(forKey: key1){
        cell.imgPicture.image = imageFromCache as! UIImage
    }else{
        DispatchQueue.global(qos: .background).async {
            let ImageString = self.vImages_api[indexPath.item]
            let imageUrl = URL(string: ImageString)
            let imageData = NSData(contentsOf: imageUrl!)
            let  myPicture = UIImage(data: imageData! as Data)
            self.objCache.setObject(poza!, forKey: ImageString as AnyObject)
                DispatchQueue.main.async {
                    if imageData != nil {
                        cell.imgPicture.image = myPicture
                    }
                }
        }

    }

    return cell
}

已编辑的代码-版本III

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = self.collectionViewPRODUSE.dequeueReusableCell(withReuseIdentifier: "celula_custom", for: indexPath) as! clsCustomCell
    cell.lblPret.text = vPrice[indexPath.item]
    cell.lblTitlu.text = vTitle[indexPath.item]

  NKPlaceholderImage(image: UIImage(named: "loading"), imageView: cell.imgPicture, imgUrl:  self.vImages_api[indexPath.item]
    ) { (image11) in
        cell.imgPicture.image = image11
    }
    cell.layer.borderColor = UIColor.lightGray.cgColor
    cell.layer.borderWidth = 0.5

    return cell
}