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

干净的方式:

extension URL {
    var favIcon16: UIImage? { getFav(ofSize: .s) }
    var favIcon32: UIImage? { getFav(ofSize: .m) }
    var favIcon64: UIImage? { getFav(ofSize: .l) }
    var favIcon128: UIImage? { getFav(ofSize: .xl) }
    var favIcon256: UIImage? { getFav(ofSize: .xxl) }
    var favIcon512: UIImage? { getFav(ofSize: .xxxl) }

    private func getFav(ofSize s: FavSize) -> UIImage? {
        guard UIApplication.shared.canOpenURL(self),
              let favUrl = URL(string: "https://www.google.com/s2/favicons?sz=\(s.rawValue)&domain=\(self.absoluteURL)"),
              let data = try? Data(contentsOf: favUrl)
        else { return nil }
        return UIImage(data: data)
 }
    private enum FavSize: Int, CaseIterable { case s = 16, m = 32, l = 64, xl = 128, xxl = 256, xxxl = 512 }
}

和用法:

let myUrl = URL(string: "http://facebook.com")
myImgView.image = myUrl.favIcon16

其他回答

斯威夫特5

extension UIImageView {
    func load(url: URL) {
        DispatchQueue.global().async { [weak self] in
            if let data = try? Data(contentsOf: url) {
                if let image = UIImage(data: data) {
                    DispatchQueue.main.async {
                        self?.image = image
                    }
                }
            }
        }
    }
}

使用

override func awakeFromNib() {
    super.awakeFromNib()
   if let url = URL(string:"<imageURLHere>"){
     imgView.load(url: url)
   }
}

你需要做的是:

UIImage(data: data)

在Swift中,他们已经用规则构造函数取代了大多数Objective C工厂方法。

See:

https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/InteractingWithObjective-CAPIs.html#//apple_ref/doc/uid/TP40014216-CH4-XID_26

斯威夫特2。x答案下载图像到文件(与Leo Dabus的答案相反,它将图像存储在内存中)。根据Leo Dabus的回答和Rob的回答,从完成处理程序的NSURLSession DownloadTaskWithRequest中获取数据:

    // Set download vars
    let downloadURL = NSURL() // URL to download from
    let localFilename = "foobar.png" // Filename for storing locally 

    // Create download request
    let task = NSURLSession.sharedSession().downloadTaskWithURL(downloadURL) { location, response, error in
        guard location != nil && error == nil else {
            print("Error downloading message: \(error)")
            return
        }

        // If here, no errors so save message to permanent location
        let fileManager = NSFileManager.defaultManager()
        do {
            let documents = try fileManager.URLForDirectory(.DocumentDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: false)
            let fileURL = documents.URLByAppendingPathComponent(localFilename)
            try fileManager.moveItemAtURL(location!, toURL: fileURL)
            self.doFileDownloaded(fileURL, localFilename: localFilename)
            print("Downloaded message @ \(localFilename)")
        } catch {
            print("Error downloading message: \(error)")
        }
    }

    // Start download
    print("Starting download @ \(downloadURL)")
    task.resume()


// Helper function called after file successfully downloaded
private func doFileDownloaded(fileURL: NSURL, localFilename: String) {

    // Do stuff with downloaded image

}
class ImageStore: NSObject { 
    static let imageCache = NSCache<NSString, UIImage>()
}

extension UIImageView {
    func url(_ url: String?) {
        DispatchQueue.global().async { [weak self] in
            guard let stringURL = url, let url = URL(string: stringURL) else {
                return
            }
            func setImage(image:UIImage?) {
                DispatchQueue.main.async {
                    self?.image = image
                }
            }
            let urlToString = url.absoluteString as NSString
            if let cachedImage = ImageStore.imageCache.object(forKey: urlToString) {
                setImage(image: cachedImage)
            } else if let data = try? Data(contentsOf: url), let image = UIImage(data: data) {
                DispatchQueue.main.async {
                    ImageStore.imageCache.setObject(image, forKey: urlToString)
                    setImage(image: image)
                }
            }else {
                setImage(image: nil)
            }
        }
    }
}

用法:

let imageView = UIImageView()
imageView.url("image url")

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")