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。
我把这个问题的最佳答案的代码包装成一个单一的，可重用的类扩展UIImageView，所以你可以直接在你的故事板中使用异步加载UIImageViews(或从代码中创建它们)。
这是我的班级:
import Foundation
import UIKit
class UIImageViewAsync :UIImageView
{
override init()
{
super.init(frame: CGRect())
}
override init(frame:CGRect)
{
super.init(frame:frame)
}
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
func getDataFromUrl(url:String, completion: ((data: NSData?) -> Void)) {
NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: url)!) { (data, response, error) in
completion(data: NSData(data: data))
}.resume()
}
func downloadImage(url:String){
getDataFromUrl(url) { data in
dispatch_async(dispatch_get_main_queue()) {
self.contentMode = UIViewContentMode.ScaleAspectFill
self.image = UIImage(data: data!)
}
}
}
}
下面是如何使用它:
imageView.downloadImage("http://www.image-server.com/myImage.jpg")
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
}
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")
您可以使用pod SDWebImage来实现相同的功能。它很容易使用。你可以在SDWebImage这里获得文档
下面是示例代码
self.yourImage.sd_setImage(with: NSURL(string: StrUrl as String ) as URL!, placeholderImage: placeholderImage, options: SDWebImageOptions(rawValue: 0), completed: { (image, error, cacheType, imageURL) in
if( error != nil)
{
print("Error while displaying image" , (error?.localizedDescription)! as String)
}
})
