SwiftUI ScrollView 不显示从 ObservableObject 获取的结果

Posted 2023-02-24

【中文标题】SwiftUI ScrollView 不显示从 ObservableObject 获取的结果

【英文标题】：SwiftUI ScrollView doesn't show fetched results from an ObservableObject

【发布时间】：2019-11-23 12:08:27

【问题描述】：

我正在尝试通过单击“获取”按钮从 api 获取数据，并通过 ScrollView 中的 ForEach 循环显示它们。

我正在使用 MVVM 模型。提取本身发生在 ObservableObject 类中。

不幸的是，ScrollView 没有显示内容。如果我使用 List 而不是 ScrollView 它可以正常工作。

你知道我在这里缺少什么吗？

非常感谢您的帮助！

import SwiftUI

struct Photo: Identifiable, Decodable 

    let id = UUID()
    let title: String


class ContentViewModel: ObservableObject 

    let api = "https://jsonplaceholder.typicode.com/photos"

    @Published var photos: [Photo] = []

    func fetchData() 
        print("Fetching started")
        guard let url = URL(string: api) else  return 

        URLSession.shared.dataTask(with: url)  data, _, _ in
            DispatchQueue.main.async 
                self.photos = try! JSONDecoder().decode([Photo].self, from: data!)
                print("Fetching successfull. Fetched \(self.photos.count) photos.")
            
        .resume()
    


struct ContentView: View 

    @ObservedObject var contentVM = ContentViewModel()

    var body: some View 
        NavigationView 
            ScrollView 
                ForEach(self.contentVM.photos)  photo in
                    Text(photo.title)
                
            
            .navigationBarTitle("Home")
            .navigationBarItems(trailing: Button(action: 

                self.contentVM.fetchData()

                , label: 
                    Text("Fetch")
            ))
        
    


struct ContentView_Previews: PreviewProvider 
    static var previews: some View 
        ContentView()
    

【参考方案1】：

你没有错过任何东西，我认为问题在于渲染内容。即使在您的示例数据显示在真实设备（iPhone 7 ios 13.1.1）上，但延迟很长。尝试减少内容或帮助ScrollView 对齐。我试过了——在设备上运行得更快，但只在设备上：

class ContentViewModel: ObservableObject 

    let api = "https://jsonplaceholder.typicode.com/photos"

    @Published var photos: [Photo] = []
    @Published var first100Photos: [Photo] = []

    func fetchData() 
        print("Fetching started")
        guard let url = URL(string: api) else  return 

        URLSession.shared.dataTask(with: url)  data, _, _ in
            DispatchQueue.main.async 
                self.photos = try! JSONDecoder().decode([Photo].self, from: data!)
                for index in 0...100 
                    self.first100Photos.append(self.photos[index])
                
                print("Fetching successfull. Fetched \(self.photos.count) photos.")
            
        .resume()
    


struct ContentView: View 

    @ObservedObject var contentVM = ContentViewModel()

    var body: some View 
        NavigationView 
            ScrollView(.vertical) 
                VStack 
                    ForEach(self.contentVM.first100Photos)  photo in
                        Text(photo.title)
                    
                

            
            .navigationBarTitle("Home")
            .navigationBarItems(trailing: Button(action: 

                self.contentVM.fetchData()

                , label: 
                    Text("Fetch")
            ))