Ios 异步图像加载到UITableViewCell后滚动时,Swift图像会变为错误图像
我正在尝试在FriendsTableView(UITableView)单元格中异步加载图片。图像加载良好,但当我滚动表格时,图像会更改几次,错误的图像被分配到错误的单元格 我已经尝试了在StackOverflow中可以找到的所有方法,包括向原始文件添加一个标记,然后检查它,但都不起作用。我还在验证应该使用indexPath更新的单元格,并检查该单元格是否存在。所以我不知道为什么会这样 这是我的密码:Ios 异步图像加载到UITableViewCell后滚动时,Swift图像会变为错误图像,ios,swift,image,uitableview,asynchronous,Ios,Swift,Image,Uitableview,Asynchronous,我正在尝试在FriendsTableView(UITableView)单元格中异步加载图片。图像加载良好,但当我滚动表格时,图像会更改几次,错误的图像被分配到错误的单元格 我已经尝试了在StackOverflow中可以找到的所有方法,包括向原始文件添加一个标记,然后检查它,但都不起作用。我还在验证应该使用indexPath更新的单元格,并检查该单元格是否存在。所以我不知道为什么会这样 这是我的密码: func tableView(tableView: UITableView, cellF
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("friendCell", forIndexPath: indexPath) as! FriendTableViewCell
var avatar_url: NSURL
let friend = sortedFriends[indexPath.row]
//Style the cell image to be round
cell.friendAvatar.layer.cornerRadius = 36
cell.friendAvatar.layer.masksToBounds = true
//Load friend photo asyncronisly
avatar_url = NSURL(string: String(friend["friend_photo_url"]))!
if avatar_url != "" {
getDataFromUrl(avatar_url) { (data, response, error) in
dispatch_async(dispatch_get_main_queue()) { () -> Void in
guard let data = data where error == nil else { return }
let thisCell = tableView.cellForRowAtIndexPath(indexPath)
if (thisCell) != nil {
let updateCell = thisCell as! FriendTableViewCell
updateCell.friendAvatar.image = UIImage(data: data)
}
}
}
}
cell.friendNameLabel.text = friend["friend_name"].string
cell.friendHealthPoints.text = String(friend["friend_health_points"])
return cell
}
这是因为UITableView重用单元格。以这种方式加载它们会导致异步请求在不同的时间返回,从而打乱顺序 我建议你使用一些图书馆,这将使你的生活更容易像翠鸟。它将为您下载和缓存图像。此外,您不必担心异步调用 您的代码与此类似:
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("friendCell", forIndexPath: indexPath) as! FriendTableViewCell
var avatar_url: NSURL
let friend = sortedFriends[indexPath.row]
//Style the cell image to be round
cell.friendAvatar.layer.cornerRadius = 36
cell.friendAvatar.layer.masksToBounds = true
//Load friend photo asyncronisly
avatar_url = NSURL(string: String(friend["friend_photo_url"]))!
if avatar_url != "" {
cell.friendAvatar.kf_setImageWithURL(avatar_url)
}
cell.friendNameLabel.text = friend["friend_name"].string
cell.friendHealthPoints.text = String(friend["friend_health_points"])
return cell
}
在cellForRowAtIndexPath上: 1) 为自定义单元格指定索引值。比如说,
cell.tag = indexPath.row
2) 在主线程上,在分配图像之前,通过将图像与标记匹配来检查图像是否属于相应的单元格
dispatch_async(dispatch_get_main_queue(), ^{
if(cell.tag == indexPath.row) {
UIImage *tmpImage = [[UIImage alloc] initWithData:imgData];
thumbnailImageView.image = tmpImage;
}});
});
更新 有一些很棒的开源库用于图像缓存,比如和。我建议您尝试其中之一,而不是编写自己的实现 结束更新 因此,为了让它工作,您需要做几件事。首先让我们看看缓存代码
// Global variable or stored in a singleton / top level object (Ex: AppCoordinator, AppDelegate)
let imageCache = NSCache<NSString, UIImage>()
extension UIImageView {
func downloadImage(from imgURL: String) -> URLSessionDataTask? {
guard let url = URL(string: imgURL) else { return nil }
// set initial image to nil so it doesn't use the image from a reused cell
image = nil
// check if the image is already in the cache
if let imageToCache = imageCache.object(forKey: imgURL as NSString) {
self.image = imageToCache
return nil
}
// download the image asynchronously
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if let err = error {
print(err)
return
}
DispatchQueue.main.async {
// create UIImage
let imageToCache = UIImage(data: data!)
// add image to cache
imageCache.setObject(imageToCache!, forKey: imgURL as NSString)
self.image = imageToCache
}
}
task.resume()
return task
}
}
要在TableView或CollectionView单元格中使用此选项,您需要在prepareforeuse
中将图像重置为nil,然后取消下载任务。(谢谢你指出这一点
请记住,即使您使用第三方库,您仍然希望在
prepareForReuse
中取消图像并取消任务。我所拥有的解决此问题的最佳方案是Swift 3或Swift 4
只需写这两行
cell.videoImage.image = nil
cell.thumbnailimage.setImageWith(imageurl!)
根据实施情况,可能有许多事情会导致这里的所有答案都不起作用(包括我的)。检查标记对我来说不起作用,检查缓存也不起作用,我有一个自定义的Photo类,其中包含完整的图像、缩略图和更多数据,因此我也必须注意这一点,而不仅仅是防止图像被不正确地重用。因为在下载完图像后,您可能会将图像分配给cell imageView,y您需要取消下载并在prepareForReuse()上重置所需的任何内容 例如,如果您正在使用类似SDWebImage的内容
override func prepareForReuse() {
super.prepareForReuse()
self.imageView.sd_cancelCurrentImageLoad()
self.imageView = nil
//Stop or reset anything else that is needed here
}
如果您已将imageview子类化并自行处理下载,请确保设置了在调用完成之前取消下载的方法,并在prepareforuse()上调用取消
e、 g
您也可以从UIViewController中取消此操作。此操作本身或与某些答案结合使用将很可能解决此问题。Swift 3
DispatchQueue.main.async(execute: {() -> Void in
if cell.tag == indexPath.row {
var tmpImage = UIImage(data: imgData)
thumbnailImageView.image = tmpImage
}
})
我只需实现一个自定义的UIImage
类就解决了这个问题,并且我做了一个String
条件,如下代码所示:
let imageCache = NSCache<NSString, UIImage>()
class CustomImageView: UIImageView {
var imageUrlString: String?
func downloadImageFrom(withUrl urlString : String) {
imageUrlString = urlString
let url = URL(string: urlString)
self.image = nil
if let cachedImage = imageCache.object(forKey: urlString as NSString) {
self.image = cachedImage
return
}
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: NSString(string: urlString))
if self.imageUrlString == urlString {
self.image = image
}
}
}
}).resume()
}
}
让imageCache=NSCache()
类CustomImageView:UIImageView{
var imageUrlString:String?
func downloadImageFrom(带URL urlString:String){
imageUrlString=urlString
让url=url(字符串:urlString)
self.image=nil
如果让cachedImage=imageCache.object(forKey:urlString作为NSString){
self.image=cachedImage
返回
}
URLSession.shared.dataTask(带有:url!,completionHandler:{(数据,响应,错误)的
如果错误!=nil{
打印(错误!)
返回
}
DispatchQueue.main.async{
如果让image=UIImage(数据:data!){
setObject(image,forKey:NSString(string:urlString))
如果self.imageUrlString==urlString{
self.image=image
}
}
}
})1.简历()
}
}
它适合我。如果目标是iOS 13或更高版本,您可以使用和。请参阅WWDC 2019视频
这样做的目的是让单元格跟踪“发布者”,并让prepareforeuse
:
class CustomCell: UITableViewCell {
@IBOutlet weak var customImageView: UIImageView!
private weak var task: URLSessionTask?
override func prepareForReuse() {
super.prepareForReuse()
task?.cancel()
customImageView?.image = nil
}
func setImage(to url: URL) {
task = ImageManager.shared.imageTask(for: url) { result in
switch result {
case .failure(let error): print(error)
case .success(let image): self.customImageView.image = image
}
}
}
}
- 取消先前的图像请求
- 将图像视图的
image
属性设置为nil
(或占位符);然后
- 启动另一个映像请求
例如:
extension ViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return objects.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "CustomCell", for: indexPath) as! CustomCell
let url = ...
cell.setImage(to: url)
return cell
}
}
class CustomCell: UITableViewCell {
@IBOutlet weak var customImageView: UIImageView!
private var subscriber: AnyCancellable?
override func prepareForReuse() {
super.prepareForReuse()
subscriber?.cancel()
customImageView?.image = nil
}
func setImage(to url: URL) {
subscriber = ImageManager.shared.imagePublisher(for: url, errorImage: UIImage(systemName: "xmark.octagon"))
.assign(to: \.customImageView.image, on: self)
}
}
其中:
class ImageManager {
static let shared = ImageManager()
private init() { }
private let session: URLSession = {
let configuration = URLSessionConfiguration.default
configuration.requestCachePolicy = .returnCacheDataElseLoad
let session = URLSession(configuration: configuration)
return session
}()
enum ImageManagerError: Error {
case invalidResponse
}
func imagePublisher(for url: URL, errorImage: UIImage? = nil) -> AnyPublisher<UIImage?, Never> {
session.dataTaskPublisher(for: url)
.tryMap { data, response in
guard
let httpResponse = response as? HTTPURLResponse,
200..<300 ~= httpResponse.statusCode,
let image = UIImage(data: data)
else {
throw ImageManagerError.invalidResponse
}
return image
}
.replaceError(with: errorImage)
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
}
}
class ImageManager {
static let shared = ImageManager()
private init() { }
private let session: URLSession = {
let configuration = URLSessionConfiguration.default
configuration.requestCachePolicy = .returnCacheDataElseLoad
let session = URLSession(configuration: configuration)
return session
}()
enum ImageManagerError: Error {
case invalidResponse
}
@discardableResult
func imageTask(for url: URL, completion: @escaping (Result<UIImage, Error>) -> Void) -> URLSessionTask {
let task = session.dataTask(with: url) { data, response, error in
guard let data = data else {
DispatchQueue.main.async { completion(.failure(error!)) }
return
}
guard
let httpResponse = response as? HTTPURLResponse,
200..<300 ~= httpResponse.statusCode,
let image = UIImage(data: data)
else {
DispatchQueue.main.async { completion(.failure(ImageManagerError.invalidResponse)) }
return
}
DispatchQueue.main.async { completion(.success(image)) }
}
task.resume()
return task
}
}
其中:
class ImageManager {
static let shared = ImageManager()
private init() { }
private let session: URLSession = {
let configuration = URLSessionConfiguration.default
configuration.requestCachePolicy = .returnCacheDataElseLoad
let session = URLSession(configuration: configuration)
return session
}()
enum ImageManagerError: Error {
case invalidResponse
}
func imagePublisher(for url: URL, errorImage: UIImage? = nil) -> AnyPublisher<UIImage?, Never> {
session.dataTaskPublisher(for: url)
.tryMap { data, response in
guard
let httpResponse = response as? HTTPURLResponse,
200..<300 ~= httpResponse.statusCode,
let image = UIImage(data: data)
else {
throw ImageManagerError.invalidResponse
}
return image
}
.replaceError(with: errorImage)
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
}
}
class ImageManager {
static let shared = ImageManager()
private init() { }
private let session: URLSession = {
let configuration = URLSessionConfiguration.default
configuration.requestCachePolicy = .returnCacheDataElseLoad
let session = URLSession(configuration: configuration)
return session
}()
enum ImageManagerError: Error {
case invalidResponse
}
@discardableResult
func imageTask(for url: URL, completion: @escaping (Result<UIImage, Error>) -> Void) -> URLSessionTask {
let task = session.dataTask(with: url) { data, response, error in
guard let data = data else {
DispatchQueue.main.async { completion(.failure(error!)) }
return
}
guard
let httpResponse = response as? HTTPURLResponse,
200..<300 ~= httpResponse.statusCode,
let image = UIImage(data: data)
else {
DispatchQueue.main.async { completion(.failure(ImageManagerError.invalidResponse)) }
return
}
DispatchQueue.main.async { completion(.success(image)) }
}
task.resume()
return task
}
}
类图像管理器{
静态let shared=ImageManager()
私有init(){}
私有let会话:URLSession={
let configuration=URLSessionConfiguration.default
configuration.requestCachePolicy=.returnCacheDataElseLoad
let session=URLSession(配置:配置)
返回会话
}()
枚举ImageManager错误:错误{
案例无效应答
}
@可丢弃结果
func imageTask(对于url:url,完成:@escaping(Result)->Void)->URLSessionTask{
让task=session.dataTask(with:url){data,response,中的错误
guard let data=其他数据{
DispatchQueue.main.async{completion(.failure(error!))}
返回
}
警卫
让httpResponse=响应为?HTTPURLResponse,
200..TableView重用单元格。请尝试以下操作:
import UIKit
class CustomViewCell: UITableViewCell {
@IBOutlet weak var imageView: UIImageView!
private var task: URLSessionDataTask?
override func prepareForReuse() {
super.prepareForReuse()
task?.cancel()
imageView.image = nil
}
func configureWith(url string: String) {
guard let url = URL(string: string) else { return }
task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if let data = data, let image = UIImage(data: data) {
DispatchQueue.main.async {
self.imageView.image = image
}
}
}
task?.resume()
}
}
因为TableView重用单元格。请在单元格类中尝试以下代码:
class CustomViewCell: UITableViewCell {
@IBOutlet weak var catImageView: UIImageView!
private var task: URLSessionDataTask?
override func prepareForReuse() {
super.prepareForReuse()
task?.cancel()
catImageView.image = nil
}
func configureWith(url string: String) {
guard let url = URL(string: string) else { return }
task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if let data = data, let image = UIImage(data: data) {
DispatchQueue.main.async {
self.catImageView.image = image
}
}
}
task?.resume()
}
}
我在我的模型中创建了一个新的UIImage变量,并在创建新模型实例时从那里加载图像/占位符。它工作得非常好。下载后在内存和磁盘上使用翠鸟缓存就是一个例子。
它取代了传统的UrlSession下载,避免了在向下滚动TableViewCell后重新下载UIImageView
class CustomViewCell: UITableViewCell {
@IBOutlet weak var catImageView: UIImageView!
private var task: URLSessionDataTask?
override func prepareForReuse() {
super.prepareForReuse()
task?.cancel()
catImageView.image = nil
}
func configureWith(url string: String) {
guard let url = URL(string: string) else { return }
task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if let data = data, let image = UIImage(data: data) {
DispatchQueue.main.async {
self.catImageView.image = image
}
}
}
task?.resume()
}
}
sucess
Image Size:
(460.0, 460.0)
Cache:
disk
Source:
network(Kingfisher.ImageResource(cacheKey: "https://avatars0.githubusercontent.com/u/5936?v=4", downloadURL: https://avatars0.githubusercontent.com/u/5936?v=4))
Original source:
network(Kingfisher.ImageResource(cacheKey: "https://avatars0.githubusercontent.com/u/5936?v=4", downloadURL: https://avatars0.githubusercontent.com/u/5936?v=4))