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。
从服务器加载图像:-
func downloadImage(from url: URL , success:@escaping((_ image:UIImage)->()),failure:@escaping ((_ msg:String)->())){
print("Download Started")
getData(from: url) { data, response, error in
guard let data = data, error == nil else {
failure("Image cant download from G+ or fb server")
return
}
print(response?.suggestedFilename ?? url.lastPathComponent)
print("Download Finished")
DispatchQueue.main.async() {
if let _img = UIImage(data: data){
success(_img)
}
}
}
}
func getData(from url: URL, completion: @escaping (Data?, URLResponse?, Error?) -> ()) {
URLSession.shared.dataTask(with: url, completionHandler: completion).resume()
}
用法:-
if let url = URL(string: "http://www.apple.com/euro/ios/ios8/a/generic/images/og.png") {
self.downloadImage(from:url , success: { (image) in
print(image)
}, failure: { (failureReason) in
print(failureReason)
})
}
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)
}
})
(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