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。
斯威夫特4
这个方法将从一个网站异步下载图像并缓存它:
func getImageFromWeb(_ urlString: String, closure: @escaping (UIImage?) -> ()) {
guard let url = URL(string: urlString) else {
return closure(nil)
}
let task = URLSession(configuration: .default).dataTask(with: url) { (data, response, error) in
guard error == nil else {
print("error: \(String(describing: error))")
return closure(nil)
}
guard response != nil else {
print("no response")
return closure(nil)
}
guard data != nil else {
print("no data")
return closure(nil)
}
DispatchQueue.main.async {
closure(UIImage(data: data!))
}
}; task.resume()
}
在使用:
getImageFromWeb("http://www.apple.com/euro/ios/ios8/a/generic/images/og.png") { (image) in
if let image = image {
let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
imageView.image = image
self.view.addSubview(imageView)
} // if you use an Else statement, it will be in background
}
Swift 3错误处理
let url = URL(string: arr[indexPath.row] as! String)
if url != nil {
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 {
if data != nil {
cell.imgView.image = UIImage(data:data!)
}else{
cell.imgView.image = UIImage(named: "default.png")
}
}
}
}
与扩展
extension UIImageView {
func setCustomImage(_ imgURLString: String?) {
guard let imageURLString = imgURLString else {
self.image = UIImage(named: "default.png")
return
}
DispatchQueue.global().async { [weak self] in
let data = try? Data(contentsOf: URL(string: imageURLString)!)
DispatchQueue.main.async {
self?.image = data != nil ? UIImage(data: data!) : UIImage(named: "default.png")
}
}
}
}
扩展使用
myImageView. setCustomImage("url")
具有缓存支持
let imageCache = NSCache<NSString, UIImage>()
extension UIImageView {
func loadImageUsingCacheWithURLString(_ URLString: String, placeHolder: UIImage?) {
self.image = nil
if let cachedImage = imageCache.object(forKey: NSString(string: URLString)) {
self.image = cachedImage
return
}
if let url = URL(string: URLString) {
URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
//print("RESPONSE FROM API: \(response)")
if error != nil {
print("ERROR LOADING IMAGES FROM URL: \(String(describing: error))")
DispatchQueue.main.async { [weak self] in
self?.image = placeHolder
}
return
}
DispatchQueue.main.async { [weak self] in
if let data = data {
if let downloadedImage = UIImage(data: data) {
imageCache.setObject(downloadedImage, forKey: NSString(string: URLString))
self?.image = downloadedImage
}
}
}
}).resume()
}
}
}
Swift 2.0:
1)
if let url = NSURL(string: "http://etc...") {
if let data = NSData(contentsOfURL: url) {
imageURL.image = UIImage(data: data)
}
}
OR
imageURL.image =
NSURL(string: "http:// image name...")
.flatMap { NSData(contentsOfURL: $0) }
.flatMap { UIImage(data: $0) }
2)将此方法添加到VC或Extension中。
func load_image(urlString:String)
{ let imgURL: NSURL = NSURL(string: urlString)!
let request: NSURLRequest = NSURLRequest(URL: imgURL)
NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) { (response: NSURLResponse?, data: NSData?, error: NSError?) in
if error == nil {
self.image_element.image = UIImage(data: data)
}
}
}
用法:
self.load_image(" url strig here")
Swift 4:一个简单的小图像加载器(例如:缩略图)，使用NSCache，总是运行在主线程上:
class ImageLoader {
private static let cache = NSCache<NSString, NSData>()
class func image(for url: URL, completionHandler: @escaping(_ image: UIImage?) -> ()) {
DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async {
if let data = self.cache.object(forKey: url.absoluteString as NSString) {
DispatchQueue.main.async { completionHandler(UIImage(data: data as Data)) }
return
}
guard let data = NSData(contentsOf: url) else {
DispatchQueue.main.async { completionHandler(nil) }
return
}
self.cache.setObject(data, forKey: url.absoluteString as NSString)
DispatchQueue.main.async { completionHandler(UIImage(data: data as Data)) }
}
}
}
用法:
ImageLoader.image(for: imageURL) { image in
self.imageView.image = image
}
