UIImage keeps loading all time when scroll even store in NSCache - swift

Question

I am new in iOS programming. I am creating a simple app which loads image from a particular link ( firestore ). The images are completely downloaded from the server and visible on each cell of collectionview as usual. But the problem is that when when I scroll up or down then those images keeps loading again. I think it starts downloading again because when I turn off internet connection, those images are not being loaded anymore.

Here is how i set images in each cell

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! CollectionCell

    let explore = dataAppend[indexPath.item]
    //cell.imageDisplay.text = explore.title
    if let imageUrl = explore.image {
        cell.imageDisplay.loadImageWithData(urlString: imageUrl)
    }
    //print(explore.image)
    return cell
}

Here is how loading images look like loadImageWithData(urlString: imageUrl)

let imageCache = NSCache<NSString, UIImage>()

class CustomImageView : UIImageView {

var imageUrlString: String?

func loadImageWithData (urlString: String) {

    imageUrlString = urlString
    if let imageFromCache = imageCache.object(forKey: urlString as NSString){
        self.image = imageFromCache
    }
    image = nil
    let url = URL(string: urlString)
    URLSession.shared.dataTask(with: url!, completionHandler: { (data, response, error) in

        if let err = error {
            print(err.localizedDescription)
        }
        if let data = data {

            DispatchQueue.main.async {
                let imageToCache = UIImage(data: data)
                if self.imageUrlString == urlString {
                    self.image = imageToCache
                }
                imageCache.setObject(imageToCache!, forKey: urlString as NSString)
            }
        }
    }).resume()
}
}

Take the benefit of some third party libraries (SDWebImages or KingFisher).They do image caching in better way and handle some more scenarios. — Vikky, Aug 02 '18 at 05:34

Muhammed Azharudheen · Accepted Answer · 2018-08-02T04:57:14.393

2

 var imageCache = NSMutableDictionary()

class CustomImageView: UIImageView {

func loadImageUsingCacheWithUrlString(urlString: String) {

    self.image = nil

    if let img = imageCache.valueForKey(urlString) as? UIImage{
        self.image = img
         return 
    }
        let session = NSURLSession.sharedSession()
        let task = session.dataTaskWithURL(NSURL(string: urlString)!, completionHandler: { (data, response, error) -> Void in

            if(error == nil){

                if let img = UIImage(data: data!) {
                    imageCache.setValue(img, forKey: urlString)    // Image saved for cache
                    DispatchQuee.main.asyn{
                       self.image = img

                }


            }
        })
        task.resume()
    }
}

}

edited Aug 02 '18 at 04:57

answered Aug 02 '18 at 04:34

Muhammed Azharudheen

181
8

it really solve my problem, thank you. So i have one doubt that i want know it that, if user kill app then it will start to downloading again, right? How about facebook, even i kill app but still some images are still showing? Do you this technique? – Visal Sambo Aug 02 '18 at 04:47
if it is stored in cache, killing app will not remove the image, unless you clear cache. – Muhammed Azharudheen Aug 02 '18 at 04:48
Ohh! Now i kill my app and it starts downloading again? Why? – Visal Sambo Aug 02 '18 at 04:49
If I don’t kill app, i just enter background for few minutes and some images keep loading again. Why sir? – Visal Sambo Aug 02 '18 at 04:51
i edited answer please check the same. maybe you are declaring the cache inside the class. – Muhammed Azharudheen Aug 02 '18 at 04:57
I will check sir! – Visal Sambo Aug 02 '18 at 05:09
Will i use URLSession instead of NSURLSession ? – Visal Sambo Aug 02 '18 at 05:10
you can also go for sdwebimage or kingfisher library. they are doing good for imagecaching. – Muhammed Azharudheen Aug 02 '18 at 05:17

score 1 · Answer 2 · answered Aug 02 '18 at 11:05

You can instead use the Kingfisher library , handles the image caching itself you don't need to worry about it. For implementing see : https://github.com/onevcat/Kingfisher

with just one line of code you can set the image

imgView.kf.setImage(with: ImageResource(downloadURL: URL(string: imgUrl)!))

UIImage keeps loading all time when scroll even store in NSCache - swift

2 Answers2