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。
一个快速的黑客，如果你想快速检查图像从url
let imageURL = NSURL(string: "https://farm2.staticflickr.com/1591/26078338233_d1466b7da2_m.jpg")
let imagedData = NSData(contentsOfURL: imageURL!)!
imageView?.image = UIImage(data: imagedData)
我在一个tableview中实现了一个只有图像的自定义单元格
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell{
let cell = tableView.dequeueReusableCellWithIdentifier("theCell", forIndexPath: indexPath) as! customTableViewCell
let imageURL = NSURL(string: "https://farm2.staticflickr.com/1591/26078338233_d1466b7da2_m.jpg")
let imagedData = NSData(contentsOfURL: imageURL!)!
cell.imageView?.image = UIImage(data: imagedData)
return cell
}
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()
})
}
}
}
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")
一个快速的黑客，如果你想快速检查图像从url
let imageURL = NSURL(string: "https://farm2.staticflickr.com/1591/26078338233_d1466b7da2_m.jpg")
let imagedData = NSData(contentsOfURL: imageURL!)!
imageView?.image = UIImage(data: imagedData)
我在一个tableview中实现了一个只有图像的自定义单元格
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell{
let cell = tableView.dequeueReusableCellWithIdentifier("theCell", forIndexPath: indexPath) as! customTableViewCell
let imageURL = NSURL(string: "https://farm2.staticflickr.com/1591/26078338233_d1466b7da2_m.jpg")
let imagedData = NSData(contentsOfURL: imageURL!)!
cell.imageView?.image = UIImage(data: imagedData)
return cell
}
(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
