Ios SwiftUI@ObservedObject在异步获取映像时未得到更新
我有一个应用程序,它从远程API获取一个带有图像URL的项目列表,然后它必须从该项目位置内的给定URL获取每个项目的图像。 问题是,当上下滚动从而从视图中删除列表项并将其移回视图时,它们确实会显示出来。然而,在初始加载时,它们始终处于“加载”状态,直到移出和移入。 我的代码:Ios SwiftUI@ObservedObject在异步获取映像时未得到更新,ios,swift,xcode,swiftui,combine,Ios,Swift,Xcode,Swiftui,Combine,我有一个应用程序,它从远程API获取一个带有图像URL的项目列表,然后它必须从该项目位置内的给定URL获取每个项目的图像。 问题是,当上下滚动从而从视图中删除列表项并将其移回视图时,它们确实会显示出来。然而,在初始加载时,它们始终处于“加载”状态,直到移出和移入。 我的代码: import SwiftUI struct ContentView: View { @EnvironmentObject var artObjectStore: ArtObjectStore @Stat
import SwiftUI
struct ContentView: View {
@EnvironmentObject var artObjectStore: ArtObjectStore
@State private var pageCount = 1
@State private var tappedLink: String? = nil
@Environment(\.imageCache) var cache: ImageCache
var body: some View {
NavigationView {
Form {
Section(header: Text("Art")) {
List {
ForEach(artObjectStore.artObjects, id: \.self) { artObject in
self.link(for: artObject)
}
Button(action: loadMore) {
Text("")
}
.onAppear {
DispatchQueue.global(qos: .background).asyncAfter(deadline: DispatchTime(uptimeNanoseconds: 10)) {
self.loadMore()
}
}
}
}
}
.navigationBarTitle("Art objects")
}
.onAppear(perform: loadMore)
}
func loadMore() {
pageCount += 1
artObjectStore.loadMore(pageCount)
}
private func link(for artObject: ArtObject) -> some View {
let selection = Binding(get: { self.tappedLink },
set: {
UIApplication.shared.endEditing()
self.tappedLink = $0
})
return NavigationLink(destination: DetailView(artObject: artObject, cache: self.cache),
tag: artObject.id,
selection: selection) {
HStack(alignment: .center) {
VStack(alignment: .leading){
Text("\(artObject.title)").font(.system(size: 12))
Text("\(artObject.principalOrFirstMaker)").font(.system(size: 9)).foregroundColor(.gray)
}
Spacer()
AsyncImage(
url: URL(string: artObject.headerImage.url)!,
cache: self.cache,
width: 200,
height: 50
)
}
}
}
}
extension UIApplication {
func endEditing() {
sendAction(#selector(UIResponder.resignFirstResponder), to: nil, from: nil, for: nil)
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
图像容器:
import SwiftUI
import Combine
import Foundation
class ImageLoader: ObservableObject {
let objectWillChange = ObservableObjectPublisher()
private var cancellable: AnyCancellable?
@Published var image: UIImage? {
willSet {
objectWillChange.send()
}
}
private let url: URL
private var cache: ImageCache?
init(url: URL, cache: ImageCache? = nil) {
self.url = url
self.cache = cache
}
deinit {
cancellable?.cancel()
}
private func cache(_ image: UIImage?) {
image.map { cache?[url] = $0 }
}
func load() {
if let image = cache?[url] {
self.image = image
return
}
cancellable = URLSession.shared.dataTaskPublisher(for: url)
.map { UIImage(data: $0.data) }
.replaceError(with: nil)
.handleEvents(receiveOutput: { [weak self] in self?.cache($0) })
.receive(on: DispatchQueue.main)
.assign(to: \.image, on: self)
}
func cancel() {
cancellable?.cancel()
}
}
struct AsyncImage: View {
@ObservedObject private var loader: ImageLoader
private let width: CGFloat?
private let height: CGFloat?
@State var spin = false
init(url: URL, cache: ImageCache? = nil, width: CGFloat? = nil, height: CGFloat? = nil) {
loader = ImageLoader(url: url, cache: cache)
self.width = width
self.height = height
}
var body: some View {
image
.onAppear(perform: loader.load)
.onDisappear(perform: loader.cancel)
}
private var image: some View {
Group {
if loader.image != nil {
Image(uiImage: loader.image!)
.resizable()
.aspectRatio(contentMode: .fit)
.frame(width: width, height: height)
} else {
Image("loadingCircle")
.resizable()
.frame(width: 20, height: 20)
.rotationEffect(.degrees(spin ? 360 : 0))
.animation(Animation.linear(duration: 0.8).repeatForever(autoreverses: false))
.onAppear() {
self.spin.toggle()
}
}
}
}
}
protocol ImageCache {
subscript(_ url: URL) -> UIImage? { get set }
}
struct TemporaryImageCache: ImageCache {
private let cache = NSCache<NSURL, UIImage>()
subscript(_ key: URL) -> UIImage? {
get { cache.object(forKey: key as NSURL) }
set { newValue == nil ? cache.removeObject(forKey: key as NSURL) : cache.setObject(newValue!, forKey: key as NSURL) }
}
}
struct ImageCacheKey: EnvironmentKey {
static let defaultValue: ImageCache = TemporaryImageCache()
}
extension EnvironmentValues {
var imageCache: ImageCache {
get { self[ImageCacheKey.self] }
set { self[ImageCacheKey.self] = newValue }
}
}
导入快捷界面
进口联合收割机
进口基金会
类ImageLoader:ObservableObject{
let objectWillChange=observeObjectPublisher()
私有var可取消:任何可取消?
@已发布的var图像:UIImage{
意志{
objectWillChange.send()
}
}
私有let url:url
私有变量缓存:ImageCache?
初始化(url:url,缓存:ImageCache?=nil){
self.url=url
self.cache=cache
}
脱硝{
可取消?.cancel()
}
专用func缓存(image:UIImage?){
image.map{cache?[url]=$0}
}
func load(){
如果让image=cache?[url]{
self.image=image
返回
}
Cancelable=URLSession.shared.dataTaskPublisher(for:url)
.map{UIImage(数据:$0.data)}
.replaceError(带:nil)
.handleEvents(receiveOutput:{[weak self]在self?.cache($0)中)
.receive(在:DispatchQueue.main上)
.assign(到:\.image,在:self上)
}
func cancel(){
可取消?.cancel()
}
}
结构异步映像:视图{
@ObservedObject私有变量加载程序:ImageLoader
私人出租宽度:CGFloat?
私人出租高度:CGFloat?
@状态变量spin=false
init(url:url,cache:ImageCache?=nil,宽度:CGFloat?=nil,高度:CGFloat?=nil){
loader=ImageLoader(url:url,缓存:缓存)
self.width=宽度
自我高度=高度
}
var body:一些观点{
形象
.onAppear(执行:loader.load)
.onDisappear(执行:loader.cancel)
}
私有var映像:一些视图{
团体{
如果loader.image!=nil{
图像(uiImage:loader.Image!)
.可调整大小()
.aspectRatio(内容模式:.fit)
.框架(宽度:宽度,高度:高度)
}否则{
图像(“加载循环”)
.可调整大小()
.框架(宽度:20,高度:20)
.旋转效果(.度(旋转360:0))
.animation(animation.linear(持续时间:0.8)。repeatForever(自动反转:false))
.onAppear(){
self.spin.toggle()
}
}
}
}
}
协议映像缓存{
下标(url:url)->UIImage?{get set}
}
结构临时ImageCache:ImageCache{
private let cache=NSCache()
下标(ukey:URL)->UIImage{
获取{cache.object(forKey:key作为NSURL)}
set{newValue==nil?cache.removeObject(forKey:key作为NSURL):cache.setObject(newValue!,forKey:key作为NSURL)}
}
}
结构ImageCacheKey:EnvironmentKey{
静态let defaultValue:ImageCache=TemporaryImageCache()
}
扩展环境值{
var-imageCache:imageCache{
获取{self[ImageCacheKey.self]}
设置{self[ImageCacheKey.self]=newValue}
}
}
我确实尝试在图像上添加willSet,但似乎不起作用。你能帮我吗?下面所有内容都是用Xcode 11.4/iOS 13.4测试的 修改后的图像
AsyncImage
我将Group
更改为VStack
,它开始更新
private var image: some View {
VStack { // << here !!
if loader.image != nil {
cache()函数没有被触发,我在那里添加了一个断点。很抱歉,我没有正确检查它,它不工作:(我确实得到了很多HTTP加载失败,0/0字节(错误代码:-999[1:89])我当时使用的是iOS 13.2,现在正在更新,也许是这个helps@Async-,只是想问一下您的URL是否有效,因为我测试了google image中的found,它确实存在。感觉像是一个非主线程更新。如果您在ContentView中调用loadMore而没有DispatchAsync,会发生什么情况。loadMore不必做任何事情,因为它如果只加载其他单元格,则问题在于ImageLoader.load()
class ImageLoader: ObservableObject {
@Published var image: UIImage?
private var cancellable: AnyCancellable?
private let url: URL
private var cache: ImageCache?
init(url: URL, cache: ImageCache? = nil) {
self.url = url
self.cache = cache
}
deinit {
cancellable?.cancel()
}
private func cache(_ image: UIImage?) {
self.image = image
image.map { cache?[url] = $0 }
}
func load() {
if let image = cache?[url] {
self.image = image
return
}
cancellable = URLSession.shared.dataTaskPublisher(for: url)
.map { UIImage(data: $0.data) }
.receive(on: DispatchQueue.main)
.replaceError(with: nil)
.sink(receiveValue: { [weak self] in self?.cache($0) })
}
func cancel() {
cancellable?.cancel()
}
}