如何快速将多个图像从 URL 保存到本地存储？

Question

I am developing Restaurant app. There are 340 foods data. I am getting this data from backend that developed with Laravel. App is working well in online. But, although network is turned off, All foods data should be displayed in app. So, I tried to save foods data to local. It is good to save text data to local(exactly, UserDefaults and FileSystem). But, when I try to save images to local from urls, It occur error and don't save to local exactly.

Have you ever seen such problems? If yes, I appreciate your help. Thanks

Answer 1

I don't know exactly what error you faced, but I think the answer to the link can help you.

• How do I make JSON data persistent for offline use (Swift 4)

Additionally, image data would be good to be cached.
If you communicate based on URLSession , you can process caching as below.

• Saving an Image to a Cache

  Cache.imageCache.setObject(image, forKey: url.absoluteString as NSString)

• Bring up cached images

  let cacheImage = Cache.imageCache.object(forKey: url.absoluteString as NSString)

Code

class Cache {
   static let imageCache = NSCache<NSString, UIImage>()
}


extension UIImageView {
  func imageDownload(url: URL, contentMode mode: UIView.ContentMode = .scaleAspectFit) {
    if let cacheImage = Cache.imageCache.object(forKey: url.absoluteString as NSString) {
        DispatchQueue.main.async() { [weak self] in
            self?.contentMode = mode
            self?.image = cacheImage
        }
    }
    else {
        var request = URLRequest(url: url)
        request.httpMethod = "GET"

        URLSession.shared.dataTask(with: request) { data, response, error in
            guard
                let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200,
                let mimeType = response?.mimeType, mimeType.hasPrefix("image"),
                let data = data, error == nil,
                let image = UIImage(data: data)
                else {
                    print("Download image fail : \(url)")
                    return
            }

            DispatchQueue.main.async() { [weak self] in
                print("Download image success \(url)")

                Cache.imageCache.setObject(image, forKey: url.absoluteString as NSString)

                self?.contentMode = mode
                self?.image = image
            }
         }.resume()
      }
   }
}

To make caching more convenient, use a library called Kingfisher .

• Kingfisher

Answer 2

You need to manage lazy loadings, you can use SDWebImages instead of manage it manually

SDWebImages will automatically manage your images caches and will also load them without internet here is a simple usage of it

add pod in podfile

pod 'SDWebImage'

usagae:

import SDWebImage

imageView.sd_setImage(with: URL(string: "http://www.example.com/path/to/image.jpg"), placeholderImage: UIImage(named: "placeholder.png"))