用于在 UICollectionView 中下载和显示图像的 UIImageView 扩展

Question

我制作并扩展了 UIImageView，它允许我异步下载图像，然后根据它们的特定索引（CollectionView 中的 IndexPath）将它们分配给它们的 ImageView。效果很好，唯一的问题是：

我在快速滚动和停止时仍然看到显示错误的图像。

有人可以帮帮我吗？这是我的代码：

// UIImageView 扩展：

extension ExtendedUIImageView {

func downloadFrom(link link:String, contentMode mode: UIViewContentMode, imageIndex: Int) {

    if (NSFileManager.defaultManager().fileExistsAtPath(link)) {
        self.image = UIImage(contentsOfFile: link)
        return
    }

    self.imageURL = NSURL(string: link)
    let url = NSURL(string: link)
    contentMode = mode

    NSURLSession.sharedSession().dataTaskWithURL(url!, completionHandler: { (data, response, error) -> Void in
        guard
            let httpURLResponse = response as? NSHTTPURLResponse where httpURLResponse.statusCode == 200,
            let mimeType = response?.MIMEType where mimeType.hasPrefix("image"),
            let data = data where error == nil,
            let image = UIImage(data: data)
            else { return }
        dispatch_async(dispatch_get_main_queue()) { () -> Void in
            if (url == self.imageURL) {
                self.image = image
            }
        }
    }).resume()
  }
}

// 我将像这样调用此方法：

self.previewImageView?.downloadFrom(link: localPath, contentMode: .ScaleAspectFill, imageIndex: cell.indexPath.item)

// 其中：

var previewImageView: ExtendedUIImageView?

请帮助我:-O

Answer 1

你好~我前段时间一直在尝试做同样的事情。这就是我所做的。这对我来说很简单，而且工作正常，没有任何问题。

import Foundation
import UIKit

extension UIImageView {


    //load image async from inaternet
    func loadFromURL(photoUrl:String){
        //NSURL
        let url = NSURL(string: photoUrl)
        //Request
        let request = NSURLRequest(URL:url!);
        //Session
        let session = NSURLSession.sharedSession()
        //Data task
        let datatask = session.dataTaskWithRequest(request) { (data:NSData?, response:NSURLResponse?, error:NSError?) -> Void in
            if error != nil {
                print(error?.localizedDescription)
            }
            dispatch_async(dispatch_get_main_queue()) {
                self.image = UIImage(data: data!)
            }
        }
        datatask.resume()
    }


}

Answer 2

使用 Kingfisher 进行缓存

import Foundation
import UIKit
import Kingfisher

public extension UIImageView {
    func loadAvatar(url: URL) {
        self.kf.setImage(with: url, placeholder: UIImage(named: "default-avatar"), options: [.transition(.fade(0.2))])
    }

    func setImageWithIndicator(url: URL) {
        self.kf.indicatorType = .activity
        self.kf.setImage(with: url)
    }
}

用于在 UICollectionView 中下载和显示图像的 UIImageView 扩展

UIImageView Extension for Downloading and Displaying Images in UICollectionView

uiimageview

uiimage

uicollectionview

nsurlsession

swift