Swift 迅捷为什么可以';你不能在两个视图之间传递发布者吗?
我只是想做一些这样的测试↓Swift 迅捷为什么可以';你不能在两个视图之间传递发布者吗?,swift,swiftui,combine,Swift,Swiftui,Combine,我只是想做一些这样的测试↓ 从第一个视图创建一个发布服务器 将其传递给第二视图 在第二个视图中使用某些属性绑定发布服务器,并尝试在屏幕上显示它 代码是↓ (第一视图) (第二视图) 结构响应视图:视图{ 让发布者:AnyPublisher @状态变量内容:String=“” var body:一些观点{ HStack{ VStack{ 文本(内容) .font(.system(大小:12)) .onAppear{{uu=self.publisher.assign(to:\.content,on:
2020-11-11 11:08:04.657375+0800 PandaServiceDemo[83721:1275181] Task <6B53516E-5127-4C5E-AD5F-893F1AEE77E8>.<1> finished with error [-999] Error Domain=NSURLErrorDomain Code=-999 "cancelled" UserInfo={NSErrorFailingURLStringKey=https://v.juhe.cn/joke/content/list.php?sort=asc&page=&pagesize=&time=1418816972&key=aa73ebdd8672a2b9adc9dbb2923184c8, NSLocalizedDescription=cancelled, NSErrorFailingURLKey=https://v.juhe.cn/joke/content/list.php?sort=asc&page=&pagesize=&time=1418816972&key=aa73ebdd8672a2b9adc9dbb2923184c8}
2020-11-11:08:04.657375+0800 PandaServiceDemo[83721:1275181]任务。已完成,错误为[-999]错误域=nsurErrorDomain代码=-999“已取消”用户信息={NSErrorFailingURLStringKey=https://v.juhe.cn/joke/content/list.php?sort=asc&page=&pagesize=&time=1418816972&key=aa73ebdd8672a2b9adc9dbb2923184c8,NSLocalizedDescription=已取消,NSErrorFailingURLKey=https://v.juhe.cn/joke/content/list.php?sort=asc&page=&pagesize=&time=1418816972&key=aa73ebdd8672a2b9adc9dbb2923184c8}
有人能告诉我发生了什么事,什么是做这件事的正确方法吗?好的,这项工作有两种方法:一种更好 方式1:
import SwiftUI
struct ContentView: View {
@State var urlForPublicsh: URL?
var body: some View {
VStack
{
Text(urlForPublicsh?.absoluteString ?? "nil")
.padding()
Button("Change the Publisher") {urlForPublicsh = URL(string: "https://stackoverflow.com")}
.padding()
SecondView(urlForPublicsh: $urlForPublicsh)
}
.onAppear()
{
urlForPublicsh = URL(string: "https://www.apple.com")
}
}
}
struct SecondView: View {
@Binding var urlForPublicsh: URL?
var body: some View {
Text(urlForPublicsh?.absoluteString ?? "nil")
.padding()
}
}
import SwiftUI
class UrlForPublicshModel: ObservableObject
{
static let shared = UrlForPublicshModel()
@Published var url: URL?
}
struct ContentView: View {
@StateObject var urlForPublicshModel = UrlForPublicshModel.shared
var body: some View {
VStack
{
Text(urlForPublicshModel.url?.absoluteString ?? "nil")
.padding()
Button("Change the Publisher") {urlForPublicshModel.url = URL(string: "https://stackoverflow.com")}
.padding()
SecondView()
}
.onAppear()
{
urlForPublicshModel.url = URL(string: "https://www.apple.com")
}
}
}
struct SecondView: View {
@ObservedObject var urlForPublicshModel = UrlForPublicshModel.shared
var body: some View {
Text(urlForPublicshModel.url?.absoluteString ?? "nil")
.padding()
}
}
方式2:
import SwiftUI
struct ContentView: View {
@State var urlForPublicsh: URL?
var body: some View {
VStack
{
Text(urlForPublicsh?.absoluteString ?? "nil")
.padding()
Button("Change the Publisher") {urlForPublicsh = URL(string: "https://stackoverflow.com")}
.padding()
SecondView(urlForPublicsh: $urlForPublicsh)
}
.onAppear()
{
urlForPublicsh = URL(string: "https://www.apple.com")
}
}
}
struct SecondView: View {
@Binding var urlForPublicsh: URL?
var body: some View {
Text(urlForPublicsh?.absoluteString ?? "nil")
.padding()
}
}
import SwiftUI
class UrlForPublicshModel: ObservableObject
{
static let shared = UrlForPublicshModel()
@Published var url: URL?
}
struct ContentView: View {
@StateObject var urlForPublicshModel = UrlForPublicshModel.shared
var body: some View {
VStack
{
Text(urlForPublicshModel.url?.absoluteString ?? "nil")
.padding()
Button("Change the Publisher") {urlForPublicshModel.url = URL(string: "https://stackoverflow.com")}
.padding()
SecondView()
}
.onAppear()
{
urlForPublicshModel.url = URL(string: "https://www.apple.com")
}
}
}
struct SecondView: View {
@ObservedObject var urlForPublicshModel = UrlForPublicshModel.shared
var body: some View {
Text(urlForPublicshModel.url?.absoluteString ?? "nil")
.padding()
}
}
您需要存储订阅,否则它将被取消初始化并自动取消 通常,这是这样做的:
var cancellables: Set<AnyCancellable> = []
// ...
publisher
.sink {...}
.store(in: &cancellables)
您应该小心使用上述方法,因为如果重新初始化
ResponseView
,它将获得发布者的副本(大多数发布者都是值类型),因此它将启动一个新请求
要避免这种情况,请将.share()
添加到发布服务器:
let publisher = URLSession(configuration: URLSessionConfiguration.default)
.dataTaskPublisher(...)
//...
.share()
.eraseToAnyPublisher()
这里的问题是,订阅没有存储在任何地方。您必须将其存储在
anycancelable
var中并保留订阅
在调试联合相关问题时使用.print()
操作符。我发现它非常有用
正确的方法是将发布者和订阅提取到一个
observeObject
中,并将其注入视图
或使用@StateObject
class DataProvider: ObservableObject {
@Published var content: String = ""
private var bag = Set<AnyCancellable>()
private let publisher: AnyPublisher<String, Never>
init() {
publisher = URLSession(configuration: URLSessionConfiguration.default)
.dataTaskPublisher(for: URLRequest(url: URL(string: "https://v.juhe.cn/joke/content/list.php?sort=asc&page=&pagesize=&time=1418816972&key=aa73ebdd8672a2b9adc9dbb2923184c8")!))
.map(\.data.description)
.print()
.replaceError(with: "Error!")
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
}
func loadData() {
publisher.assign(to: \.content, on: self).store(in: &bag)
}
}
struct ContentView: View {
@StateObject var dataProvider = DataProvider()
var body: some View {
NavigationView {
List {
NavigationLink(destination: ResponseView(dataProvider: dataProvider)) {
Text("Hello, World!")
}
}.navigationBarTitle("Title", displayMode: .inline)
}
}
}
struct ResponseView: View {
let dataProvider: DataProvider
var body: some View {
HStack {
VStack {
Text(dataProvider.content)
.font(.system(size: 12))
.onAppear {
self.dataProvider.loadData()
}
Spacer()
}
Spacer()
}
}
}
类数据提供程序:observeObject{
@已发布的变量内容:String=“”
私有变量包=集合()
私人出租出版商:AnyPublisher
init(){
publisher=URLSession(配置:URLSessionConfiguration.default)
.dataTaskPublisher(用于:url请求(url:url(字符串):https://v.juhe.cn/joke/content/list.php?sort=asc&page=&pagesize=&time=1418816972&key=aa73ebdd8672a2b9adc9dbb2923184c8")!))
.map(\.data.description)
.print()
.replaceError(带有:“Error!”)
.receive(在:DispatchQueue.main上)
.删除任何发布者()
}
func loadData(){
publisher.assign(到:\.content,在:self上)。store(在:&bag中)
}
}
结构ContentView:View{
@StateObject var dataProvider=dataProvider()
var body:一些观点{
导航视图{
名单{
导航链接(目标:响应视图(数据提供程序:数据提供程序)){
文本(“你好,世界!”)
}
}.navigationBarTitle(“标题”,显示模式:。内联)
}
}
}
结构响应视图:视图{
让数据提供者:数据提供者
var body:一些观点{
HStack{
VStack{
文本(dataProvider.content)
.font(.system(大小:12))
奥纳佩尔先生{
self.dataProvider.loadData()
}
垫片()
}
垫片()
}
}
}
请注意,我们使用了
@StateObject
来确保数据提供程序
实例在视图更新时不会被破坏。就SwiftUI而言,您犯了一个根本错误:从视图创建发布服务器。这意味着每隔一次都会创建一个新发布服务器entView
是实例化的,不管怎样,这种情况可能会发生很多次,SwiftUI不保证视图只实例化一次
您需要做的是将发布的数据提取到某个对象中,该对象要么从上游注入,要么由SwiftUI通过
@StateObject
进行管理。谢谢,这对我帮助很大。顺便说一句,因为@StateObject只在iOS14中工作。如果在IOS13中,我们可以做什么?@Shaggon我能想到的一种方法是使用一个大模型在顶层创建,然后注入下游。这样,您只有一个实例,并且在每个级别上,您只能发送该大模型所需的部分。唯一(大)的缺点是,该模型可以通过这种方法变大……在您的示例中,您不妨将@StateObject放在ResponseView中
class DataProvider: ObservableObject {
@Published var content: String = ""
private var bag = Set<AnyCancellable>()
private let publisher: AnyPublisher<String, Never>
init() {
publisher = URLSession(configuration: URLSessionConfiguration.default)
.dataTaskPublisher(for: URLRequest(url: URL(string: "https://v.juhe.cn/joke/content/list.php?sort=asc&page=&pagesize=&time=1418816972&key=aa73ebdd8672a2b9adc9dbb2923184c8")!))
.map(\.data.description)
.print()
.replaceError(with: "Error!")
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
}
func loadData() {
publisher.assign(to: \.content, on: self).store(in: &bag)
}
}
struct ContentView: View {
@StateObject var dataProvider = DataProvider()
var body: some View {
NavigationView {
List {
NavigationLink(destination: ResponseView(dataProvider: dataProvider)) {
Text("Hello, World!")
}
}.navigationBarTitle("Title", displayMode: .inline)
}
}
}
struct ResponseView: View {
let dataProvider: DataProvider
var body: some View {
HStack {
VStack {
Text(dataProvider.content)
.font(.system(size: 12))
.onAppear {
self.dataProvider.loadData()
}
Spacer()
}
Spacer()
}
}
}