我正在研究从 url 异步显示图像。我尝试创建一个新线程来下载图像，然后刷新
main threadfunc asyncLoadImg(product:Product,imageView:UIImageView){
let downloadQueue = dispatch_queue_create("com.myApp.processdownload", nil)
dispatch_async(downloadQueue){
let data = NSData(contentsOfURL: NSURL(string: product.productImage)!)
var image:UIImage?
if data != nil{
image = UIImage(data: data!)
}
dispatch_async(dispatch_get_main_queue()){
imageView.image = image
}
}
}
当我尝试调试时，当涉及到dispatch_async(downloadQueue)时，它会跳出func。有什么建议吗？谢谢
**Swift 5.0+ 更新代码：
extension UIImageView {
func imageFromServerURL(_ URLString: String, placeHolder: UIImage?) {
self.image = nil
//If imageurl's imagename has space then this line going to work for this
let imageServerUrl = URLString.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed) ?? ""
if let url = URL(string: imageServerUrl) {
URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
//print("RESPONSE FROM API: \(response)")
if error != nil {
print("ERROR LOADING IMAGES FROM URL: \(error)")
DispatchQueue.main.async {
self.image = placeHolder
}
return
}
DispatchQueue.main.async {
if let data = data {
if let downloadedImage = UIImage(data: data) {
self.image = downloadedImage
}
}
}
}).resume()
}
}
}
现在，无论您需要什么地方，只需执行此操作即可从服务器 url 加载图像：
简单！
在
extensionSwift3NSCacheimport UIKit
let imageCache = NSCache<NSString, AnyObject>()
extension UIImageView {
func loadImageUsingCache(withUrl urlString : String) {
let url = URL(string: urlString)
self.image = nil
// check cached image
if let cachedImage = imageCache.object(forKey: urlString as NSString) as? UIImage {
self.image = cachedImage
return
}
// if not, download image from url
URLSession.shared.dataTask(with: url!, completionHandler: { (data, response, error) in
if error != nil {
print(error!)
return
}
DispatchQueue.main.async {
if let image = UIImage(data: data!) {
imageCache.setObject(image, forKey: urlString as NSString)
self.image = image
}
}
}).resume()
}
}
希望有帮助！
继续 Shobhakar Tiwari 的回答，我认为在这些情况下，在出现错误时使用默认图像以及出于加载目的通常很有帮助，因此我将其更新为包含可选的默认图像：
斯威夫特3
extension UIImageView {
public func imageFromServerURL(urlString: String, defaultImage : String?) {
if let di = defaultImage {
self.image = UIImage(named: di)
}
URLSession.shared.dataTask(with: NSURL(string: urlString)! as URL, completionHandler: { (data, response, error) -> Void in
if error != nil {
print(error ?? "error")
return
}
DispatchQueue.main.async(execute: { () -> Void in
let image = UIImage(data: data!)
self.image = image
})
}).resume()
}
}
此解决方案使滚动速度非常快，而无需不必要的图像更新。 您必须将 url 属性添加到我们的单元格类中：
class OfferItemCell: UITableViewCell {
@IBOutlet weak var itemImageView: UIImageView!
@IBOutlet weak var titleLabel: UILabel!
var imageUrl: String?
}
并添加扩展名：
import Foundation
import UIKit
let imageCache = NSCache<AnyObject, AnyObject>()
let imageDownloadUtil: ImageDownloadUtil = ImageDownloadUtil()
extension OfferItemCell {
func loadImageUsingCacheWithUrl(urlString: String ) {
self.itemImageView.image = nil
if let cachedImage = imageCache.object(forKey: urlString as AnyObject) as? UIImage {
self.itemImageView.image = cachedImage
return
}
DispatchQueue.global(qos: .background).async {
imageDownloadUtil.getImage(url: urlString, completion: {
image in
DispatchQueue.main.async {
if self.imageUrl == urlString{
imageCache.setObject(image, forKey: urlString as AnyObject)
self.itemImageView.image = image
}
}
})
}
}
}
您还可以改进它并将一些代码提取到更通用的单元类（即 CustomCellWithImage）中，以使其更具可重用性。
这段代码可能对您有帮助。
let cacheKey = indexPath.row
if(self.imageCache?.objectForKey(cacheKey) != nil){
cell.img.image = self.imageCache?.objectForKey(cacheKey) as? UIImage
}else{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), {
if let url = NSURL(string: imgUrl) {
if let data = NSData(contentsOfURL: url) {
let image: UIImage = UIImage(data: data)!
self.imageCache?.setObject(image, forKey: cacheKey)
dispatch_async(dispatch_get_main_queue(), {
cell.img.image = image
})
}
}
})
}
使用此图像将下载并缓存，而不会滞后于表格视图滚动
加载没有
in SWIFT 4blinkchanging imagesUIImageView//MARK: - 'asyncImagesCashArray' is a global varible cashed UIImage
var asyncImagesCashArray = NSCache<NSString, UIImage>()
class AyncImageView: UIImageView {
//MARK: - Variables
private var currentURL: NSString?
//MARK: - Public Methods
func loadAsyncFrom(url: String, placeholder: UIImage?) {
let imageURL = url as NSString
if let cashedImage = asyncImagesCashArray.object(forKey: imageURL) {
image = cashedImage
return
}
image = placeholder
currentURL = imageURL
guard let requestURL = URL(string: url) else { image = placeholder; return }
URLSession.shared.dataTask(with: requestURL) { (data, response, error) in
DispatchQueue.main.async { [weak self] in
if error == nil {
if let imageData = data {
if self?.currentURL == imageURL {
if let imageToPresent = UIImage(data: imageData) {
asyncImagesCashArray.setObject(imageToPresent, forKey: imageURL)
self?.image = imageToPresent
} else {
self?.image = placeholder
}
}
} else {
self?.image = placeholder
}
} else {
self?.image = placeholder
}
}
}.resume()
}
}
在
UITableViewCellclass CatCell: UITableViewCell {
//MARK: - Outlets
@IBOutlet weak var catImageView: AyncImageView!
//MARK: - Variables
var urlString: String? {
didSet {
if let url = urlString {
catImageView.loadAsyncFrom(url: url, placeholder: nil)
}
}
}
override func awakeFromNib() {
super.awakeFromNib()
}
}
最好的方法之一是使用SDWebImage。
快速示例：
import SDWebImage
imageView.sd_setImage(with: URL(string: "ImageUrl"), placeholderImage: UIImage(named: "placeholder.png"))
目标 C 示例：
#import <SDWebImage/UIImageView+WebCache.h>
[imageView sd_setImageWithURL:[NSURL URLWithString:@"ImageUrl"]
placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
从 Swift 5.5 开始，它就像调用一个函数一样简单：
imageView.setImage(url: myImageURL, placeholder: thePlaceholder)
使用这个简单的扩展：
extension UIImageView {
func setImage(url: URL, placeholder: UIImage?) {
self.image = placeholder
Task { [weak self] in
let (data, _) = try await URLSession.shared.data(from: url)
self?.image = UIImage(data: data)
}
}
}
请注意，将使用
placeholder