我想从我的应用程序中的URL加载图像,所以我首先尝试了Objective-C和它的工作,但是,与Swift,我有一个编译错误:

'imageWithData'不可用:使用对象构造'UIImage(data:)'

我的函数:

@IBOutlet var imageView : UIImageView

override func viewDidLoad() {
    super.viewDidLoad()

    var url:NSURL = NSURL.URLWithString("http://myURL/ios8.png")
    var data:NSData = NSData.dataWithContentsOfURL(url, options: nil, error: nil)

    imageView.image = UIImage.imageWithData(data)// Error here
}

在objective - c中:

- (void)viewDidLoad {
    [super viewDidLoad];

    NSURL *url = [NSURL URLWithString:(@"http://myURL/ios8.png")];
    NSData *data = [NSData dataWithContentsOfURL:url];

    _imageView.image = [UIImage imageWithData: data];
    _labelURL.text = @"http://www.quentinroussat.fr/assets/img/iOS%20icon's%20Style/ios8.png";
 }

有人能解释一下为什么imageWithData:不能与Swift一起工作,我该如何解决这个问题。


当前回答

斯威夫特4::

这将在加载图像时显示加载器。 你可以使用NSCache临时存储图像

let imageCache = NSCache<NSString, UIImage>()
extension UIImageView {
    func loadImageUsingCache(withUrl urlString : String) {
        let url = URL(string: urlString)
        if url == nil {return}
        self.image = nil

        // check cached image
        if let cachedImage = imageCache.object(forKey: urlString as NSString)  {
            self.image = cachedImage
            return
        }

        let activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView.init(activityIndicatorStyle: .gray)
        addSubview(activityIndicator)
        activityIndicator.startAnimating()
        activityIndicator.center = self.center

        // if not, download image from url
        URLSession.shared.dataTask(with: url!, completionHandler: { (data, response, error) in
            if error != nil {
                print(error!)
                return
            }

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

        }).resume()
    }
}

用法:-

truckImageView.loadImageUsingCache(withUrl: currentTruck.logoString)

其他回答

Swift 4.1我创建了一个函数,只是传递图像url,图像生成后缓存键设置为完成块。

   class NetworkManager: NSObject {
  
  private var imageQueue = OperationQueue()
  private var imageCache = NSCache<AnyObject, AnyObject>()
  
  func downloadImageWithUrl(imageUrl: String, cacheKey: String, completionBlock: @escaping (_ image: UIImage?)-> Void) {
    
    let downloadedImage = imageCache.object(forKey: cacheKey as AnyObject)
    if let  _ = downloadedImage as? UIImage {
      completionBlock(downloadedImage as? UIImage)
    } else {
      let blockOperation = BlockOperation()
      blockOperation.addExecutionBlock({
        let url = URL(string: imageUrl)
        do {
          let data = try Data(contentsOf: url!)
          let newImage = UIImage(data: data)
          if newImage != nil {
            self.imageCache.setObject(newImage!, forKey: cacheKey as AnyObject)
            self.runOnMainThread {
              completionBlock(newImage)
            }
          } else {
            completionBlock(nil)
          }
        } catch {
          completionBlock(nil)
        }
      })
      self.imageQueue.addOperation(blockOperation)
      blockOperation.completionBlock = {
        print("Image downloaded \(cacheKey)")
      }
    }
  }
}
extension NetworkManager {
  fileprivate func runOnMainThread(block:@escaping ()->Void) {
    if Thread.isMainThread {
      block()
    } else {
      let mainQueue = OperationQueue.main
      mainQueue.addOperation({
        block()
      })
    }
  }
}

这是从URL加载/下载图像的工作代码。NSCache自动和显示占位符图像下载和加载实际图像(Swift 4 | Swift 5代码)。

func NKPlaceholderImage(image:UIImage?, imageView:UIImageView?,imgUrl:String,compate:@escaping (UIImage?) -> Void){
    
    if image != nil && imageView != nil {
        imageView!.image = image!
    }
    
    var urlcatch = imgUrl.replacingOccurrences(of: "/", with: "#")
    let documentpath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
    urlcatch = documentpath + "/" + "\(urlcatch)"
    
    let image = UIImage(contentsOfFile:urlcatch)
    if image != nil && imageView != nil
    {
        imageView!.image = image!
        compate(image)
        
    }else{
        
        if let url = URL(string: imgUrl){
            
            DispatchQueue.global(qos: .background).async {
                () -> Void in
                let imgdata = NSData(contentsOf: url)
                DispatchQueue.main.async {
                    () -> Void in
                    imgdata?.write(toFile: urlcatch, atomically: true)
                    let image = UIImage(contentsOfFile:urlcatch)
                    compate(image)
                    if image != nil  {
                        if imageView != nil  {
                            imageView!.image = image!
                        }
                    }
                }
            }
        }
    }
}

像这样使用:

// Here imgPicture = your imageView
// UIImage(named: "placeholder") is Display image brfore download and load actual image. 

NKPlaceholderImage(image: UIImage(named: "placeholder"), imageView: imgPicture, imgUrl: "Put Here your server image Url Sting") { (image) in }

如果你只是想加载图像(异步!)-只需添加这个小扩展到你的swift代码:

extension UIImageView {
    public func imageFromUrl(urlString: String) {
        if let url = NSURL(string: urlString) {
            let request = NSURLRequest(URL: url)
            NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) {
                (response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in
                if let imageData = data as NSData? {
                    self.image = UIImage(data: imageData)
                }
            }
        }
    }
}

然后这样用:

myImageView.imageFromUrl("https://robohash.org/123.png")

斯威夫特4::

这将在加载图像时显示加载器。 你可以使用NSCache临时存储图像

let imageCache = NSCache<NSString, UIImage>()
extension UIImageView {
    func loadImageUsingCache(withUrl urlString : String) {
        let url = URL(string: urlString)
        if url == nil {return}
        self.image = nil

        // check cached image
        if let cachedImage = imageCache.object(forKey: urlString as NSString)  {
            self.image = cachedImage
            return
        }

        let activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView.init(activityIndicatorStyle: .gray)
        addSubview(activityIndicator)
        activityIndicator.startAnimating()
        activityIndicator.center = self.center

        // if not, download image from url
        URLSession.shared.dataTask(with: url!, completionHandler: { (data, response, error) in
            if error != nil {
                print(error!)
                return
            }

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

        }).resume()
    }
}

用法:-

truckImageView.loadImageUsingCache(withUrl: currentTruck.logoString)

(Swift 4更新) 为了直接回答最初的问题,下面是发布的Objective-C代码片段的快速等效版本。

let url = URL(string: image.url)
let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
imageView.image = UIImage(data: data!)

免责声明:

需要注意的是,Data(contentsOf:)方法将在执行代码的同一线程中同步下载url的内容,因此不要在应用程序的主线程中调用此方法。

让相同的代码异步运行,而不阻塞UI的简单方法是使用GCD:

let url = URL(string: image.url)

DispatchQueue.global().async {
    let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
    DispatchQueue.main.async {
        imageView.image = UIImage(data: data!)
    }
}

也就是说,在现实生活中的应用程序中,如果您希望获得最佳的用户体验并避免同一映像的多次下载,您可能还希望不仅下载它们,而且缓存它们。已经有相当多的库可以无缝地做到这一点,而且它们都非常易于使用。我个人推荐翠鸟:

import Kingfisher

let url = URL(string: "url_of_your_image")
// this downloads the image asynchronously if it's not cached yet
imageView.kf.setImage(with: url) 

就是这样