Ios 是否有一种方法可以使用URLSession.shared.dataTask并行请求多个不同的资源
我在这里找到了一段关于如何在没有任何中断的情况下同时下载图像的代码Ios 是否有一种方法可以使用URLSession.shared.dataTask并行请求多个不同的资源,ios,swift,urlsession,nsurlsessiondatatask,Ios,Swift,Urlsession,Nsurlsessiondatatask,我在这里找到了一段关于如何在没有任何中断的情况下同时下载图像的代码 func loadImageRobsAnswer(with urlString: String?) { // cancel prior task, if any weak var oldTask = currentTask currentTask = nil oldTask?.cancel() // reset imageview's image self.im
func loadImageRobsAnswer(with urlString: String?) {
// cancel prior task, if any
weak var oldTask = currentTask
currentTask = nil
oldTask?.cancel()
// reset imageview's image
self.image = nil
// allow supplying of `nil` to remove old image and then return immediately
guard let urlString = urlString else { return }
// check cache
if let cachedImage = DataCache.shared.object(forKey: urlString) {
self.transition(toImage: cachedImage as? UIImage)
//self.image = cachedImage
return
}
// download
let url = URL(string: urlString)!
currentURL = url
let task = URLSession.shared.dataTask(with: url) { [weak self] data, response, error in
self?.currentTask = nil
if let error = error {
if (error as NSError).domain == NSURLErrorDomain && (error as NSError).code == NSURLErrorCancelled {
return
}
print(error)
return
}
guard let data = data, let downloadedImage = UIImage(data: data) else {
print("unable to extract image")
return
}
DataCache.shared.saveObject(object: downloadedImage, forKey: urlString)
if url == self?.currentURL {
DispatchQueue.main.async {
self?.transition(toImage: downloadedImage)
}
}
}
// save and start new task
currentTask = task
task.resume()
}
public extension UIImageView {
private static var taskKey = 0
private static var urlKey = 0
private var currentTask: URLSessionTask? {
get { return objc_getAssociatedObject(self, &UIImageView.taskKey) as? URLSessionTask }
set { objc_setAssociatedObject(self, &UIImageView.taskKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) }
}
private var currentURL: URL? {
get { return objc_getAssociatedObject(self, &UIImageView.urlKey) as? URL }
set { objc_setAssociatedObject(self, &UIImageView.urlKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) }
}}}
class DataRequest {
private static var taskKey = 0
private static var urlKey = 0
static let shared = DataRequest()
typealias ImageDataCompletion = (_ image: UIImage?, _ error: Error? ) -> Void
private var currentTask: URLSessionTask? {
get { return objc_getAssociatedObject(self, &DataRequest.taskKey) as? URLSessionTask }
set { objc_setAssociatedObject(self, &DataRequest.taskKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) }
}
private var currentURL: URL? {
get { return objc_getAssociatedObject(self, &DataRequest.urlKey) as? URL }
set { objc_setAssociatedObject(self, &DataRequest.urlKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) }
}
func downloadImage(with urlString: String?, completion: @escaping ImageDataCompletion) {
weak var oldTask = currentTask
currentTask = nil
oldTask?.cancel()
guard let urlString = urlString else { return }
if let cachedImage = DataCache.shared.object(forKey: urlString) {
DispatchQueue.main.async {
completion(cachedImage as? UIImage ,nil)
}
// self.transition(toImage: cachedImage as? UIImage)
//self.image = cachedImage
return
}
// download
let url = URL(string: urlString)!
currentURL = url
let task = URLSession.shared.dataTask(with: url) { [weak self] data, response, error in
self?.currentTask = nil
if let error = error {
if (error as NSError).domain == NSURLErrorDomain && (error as NSError).code == NSURLErrorCancelled {
return
}
completion(nil,nil)
return
}
guard let data = data, let downloadedImage = UIImage(data: data) else {
print("unable to extract image")
return
}
DataCache.shared.saveObject(object: downloadedImage, forKey: urlString)
if url == self?.currentURL {
DispatchQueue.main.async {
completion(downloadedImage ,nil)
}
}
}
// save and start new task
currentTask = task
task.resume()
}
extension UIImageView {
func setImage(url: String?) {
self.image = nil
DataRequest.shared.downloadImage(with: url) { (image, error) in
DispatchQueue.main.async {
self.image = image
}
}
}
}
URLSession.shared.dataTaskUIImageViewobjc\u getAssociatedObjectobjc\u setAssociatedObjectDataRequestUIImageViewUIImageViewUIButtonUIImageViewobjc\u getAssociatedObjectobjc\u setAssociatedObjectDataRequestDataRequestDataRequestUIImageViewUIImageViewprivate var taskKey: Void?
extension UIImageView {
private static let imageProcessingQueue = DispatchQueue(label: Bundle.main.bundleIdentifier! + ".imageprocessing", attributes: .concurrent)
private var savedTask: URLSessionTask? {
get { return objc_getAssociatedObject(self, &taskKey) as? URLSessionTask }
set { objc_setAssociatedObject(self, &taskKey, newValue, .OBJC_ASSOCIATION_RETAIN) }
}
/// Set image asynchronously.
///
/// - Parameters:
/// - url: `URL` for image resource.
/// - placeholder: `UIImage` of placeholder image. If not supplied, `image` will be set to `nil` while request is underway.
/// - shouldResize: Whether the image should be scaled to the size of the image view. Defaults to `true`.
func setImage(_ url: URL, placeholder: UIImage? = nil, shouldResize: Bool = true) {
savedTask?.cancel()
savedTask = nil
image = placeholder
if let image = ImageCache.shared[url] {
DispatchQueue.main.async {
UIView.transition(with: self, duration: 0.1, options: .transitionCrossDissolve, animations: {
self.image = image
}, completion: nil)
}
return
}
var task: URLSessionTask!
let size = bounds.size * UIScreen.main.scale
task = URLSession.shared.dataTask(with: url) { [weak self] data, response, error in
guard
error == nil,
let httpResponse = response as? HTTPURLResponse,
(200..<300) ~= httpResponse.statusCode,
let data = data
else {
return
}
UIImageView.imageProcessingQueue.async { [weak self] in
var image = UIImage(data: data)
if shouldResize {
image = image?.scaledAspectFit(to: size)
}
ImageCache.shared[url] = image
DispatchQueue.main.async {
guard
let self = self,
let savedTask = self.savedTask,
savedTask.taskIdentifier == task.taskIdentifier
else {
return
}
self.savedTask = nil
UIView.transition(with: self, duration: 0.1, options: .transitionCrossDissolve, animations: {
self.image = image
}, completion: nil)
}
}
}
task.resume()
savedTask = task
}
}
class ImageCache {
static let shared = ImageCache()
private let cache = NSCache<NSURL, UIImage>()
private var observer: NSObjectProtocol?
init() {
observer = NotificationCenter.default.addObserver(forName: UIApplication.didReceiveMemoryWarningNotification, object: nil, queue: nil) { [weak self] _ in
self?.cache.removeAllObjects()
}
}
deinit {
NotificationCenter.default.removeObserver(observer!)
}
subscript(url: URL) -> UIImage? {
get {
return cache.object(forKey: url as NSURL)
}
set {
if let data = newValue {
cache.setObject(data, forKey: url as NSURL)
} else {
cache.removeObject(forKey: url as NSURL)
}
}
}
}
话虽如此，我们确实应该将并发请求限制在合理的范围内（一次4-6个），以便在之前的请求完成（或取消）之前，它们不会尝试启动，以避免超时。典型的解决方案是使用异步
操作maxConcurrentOperationCountformat.opaqueextension UIImage {
/// Resize the image to be the required size, stretching it as needed.
///
/// - parameter newSize: The new size of the image.
/// - parameter contentMode: The `UIView.ContentMode` to be applied when resizing image.
/// Either `.scaleToFill`, `.scaleAspectFill`, or `.scaleAspectFit`.
///
/// - returns: Return `UIImage` of resized image.
func scaled(to newSize: CGSize, contentMode: UIView.ContentMode = .scaleToFill) -> UIImage? {
switch contentMode {
case .scaleToFill:
return filled(to: newSize)
case .scaleAspectFill, .scaleAspectFit:
let horizontalRatio = size.width / newSize.width
let verticalRatio = size.height / newSize.height
let ratio: CGFloat!
if contentMode == .scaleAspectFill {
ratio = min(horizontalRatio, verticalRatio)
} else {
ratio = max(horizontalRatio, verticalRatio)
}
let sizeForAspectScale = CGSize(width: size.width / ratio, height: size.height / ratio)
let image = filled(to: sizeForAspectScale)
let doesAspectFitNeedCropping = contentMode == .scaleAspectFit && (newSize.width > sizeForAspectScale.width || newSize.height > sizeForAspectScale.height)
if contentMode == .scaleAspectFill || doesAspectFitNeedCropping {
let subRect = CGRect(
x: floor((sizeForAspectScale.width - newSize.width) / 2.0),
y: floor((sizeForAspectScale.height - newSize.height) / 2.0),
width: newSize.width,
height: newSize.height)
return image?.cropped(to: subRect)
}
return image
default:
return nil
}
}
/// Resize the image to be the required size, stretching it as needed.
///
/// - parameter newSize: The new size of the image.
///
/// - returns: Resized `UIImage` of resized image.
func filled(to newSize: CGSize) -> UIImage? {
let format = UIGraphicsImageRendererFormat()
format.opaque = false
format.scale = scale
return UIGraphicsImageRenderer(size: newSize, format: format).image { _ in
draw(in: CGRect(origin: .zero, size: newSize))
}
}
/// Crop the image to be the required size.
///
/// - parameter bounds: The bounds to which the new image should be cropped.
///
/// - returns: Cropped `UIImage`.
func cropped(to bounds: CGRect) -> UIImage? {
// if bounds is entirely within image, do simple CGImage `cropping` ...
if CGRect(origin: .zero, size: size).contains(bounds) {
return cgImage?.cropping(to: bounds * scale).flatMap {
UIImage(cgImage: $0, scale: scale, orientation: imageOrientation)
}
}
// ... otherwise, manually render whole image, only drawing what we need
let format = UIGraphicsImageRendererFormat()
format.opaque = false
format.scale = scale
return UIGraphicsImageRenderer(size: bounds.size, format: format).image { _ in
let origin = CGPoint(x: -bounds.minX, y: -bounds.minY)
draw(in: CGRect(origin: origin, size: size))
}
}
/// Resize the image to fill the rectange of the specified size, preserving the aspect ratio, trimming if needed.
///
/// - parameter newSize: The new size of the image.
///
/// - returns: Return `UIImage` of resized image.
func scaledAspectFill(to newSize: CGSize) -> UIImage? {
return scaled(to: newSize, contentMode: .scaleAspectFill)
}
/// Resize the image to fit within the required size, preserving the aspect ratio, with no trimming taking place.
///
/// - parameter newSize: The new size of the image.
///
/// - returns: Return `UIImage` of resized image.
func scaledAspectFit(to newSize: CGSize) -> UIImage? {
return scaled(to: newSize, contentMode: .scaleAspectFit)
}
/// Create smaller image from `Data`
///
/// - Parameters:
/// - data: The image `Data`.
/// - maxSize: The maximum edge size.
/// - scale: The scale of the image (defaults to device scale if 0 or omitted.
/// - Returns: The scaled `UIImage`.
class func thumbnail(from data: Data, maxSize: CGFloat, scale: CGFloat = 0) -> UIImage? {
guard let imageSource = CGImageSourceCreateWithData(data as CFData, nil) else {
return nil
}
return thumbnail(from: imageSource, maxSize: maxSize, scale: scale)
}
/// Create smaller image from `URL`
///
/// - Parameters:
/// - data: The image file URL.
/// - maxSize: The maximum edge size.
/// - scale: The scale of the image (defaults to device scale if 0 or omitted.
/// - Returns: The scaled `UIImage`.
class func thumbnail(from fileURL: URL, maxSize: CGFloat, scale: CGFloat = 0) -> UIImage? {
guard let imageSource = CGImageSourceCreateWithURL(fileURL as CFURL, nil) else {
return nil
}
return thumbnail(from: imageSource, maxSize: maxSize, scale: scale)
}
private class func thumbnail(from imageSource: CGImageSource, maxSize: CGFloat, scale: CGFloat) -> UIImage? {
let scale = scale == 0 ? UIScreen.main.scale : scale
let options: [NSString: Any] = [
kCGImageSourceThumbnailMaxPixelSize: maxSize * scale,
kCGImageSourceCreateThumbnailFromImageAlways: true
]
if let scaledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, options as CFDictionary) {
return UIImage(cgImage: scaledImage, scale: scale, orientation: .up)
}
return nil
}
}
extension CGSize {
static func * (lhs: CGSize, rhs: CGFloat) -> CGSize {
return CGSize(width: lhs.width * rhs, height: lhs.height * rhs)
}
}
extension CGPoint {
static func * (lhs: CGPoint, rhs: CGFloat) -> CGPoint {
return CGPoint(x: lhs.x * rhs, y: lhs.y * rhs)
}
}
extension CGRect {
static func * (lhs: CGRect, rhs: CGFloat) -> CGRect {
return CGRect(origin: lhs.origin * rhs, size: lhs.size * rhs)
}
}