SwiftUI ListView 没有访问 ForEach 循环

Posted 2023-02-24

【中文标题】SwiftUI ListView 没有访问 ForEach 循环

【英文标题】：SwiftUI ListView is not accessing the ForEach loop

【发布时间】：2021-07-13 21:04:32

【问题描述】：

我正在使用 SwiftUI（我是新的）和 Firebase 使用 Swift 做一个项目。

我想从我从 Firebase 检索并存储在字典数组中的数据中显示 List View 的信息，这工作正常，因为我可以在控制台的列表单元格中显示我想看到的信息，但 Swift没有访问我正在读取数组数据的 ForEach 循环。

我尝试过的：

将id: \.self 添加到 ForEach 循环中。 使 CourseInfo 结构符合 Hashable 协议。

然后我意识到它实际上并没有进入 ForEach 循环。

我会在下面留下我的代码。

谢谢。

Course.swift

import Foundation
import FirebaseAuth
import FirebaseFirestore

struct CourseInfo:Identifiable 
    let id = UUID()
    let courseName: String
    let totalStudents: Int
    let courseID: String


class Course: ObservableObject 
    let user = Auth.auth().currentUser
    let db = Firestore.firestore()
  
    @Published var courses = [CourseInfo]()
    
    func retreiveData() 
        // Check if the user is signed in.
        if user != nil 
            // if user is signed in --> retreive all of the user's courses and info.
            db.collection("courses").getDocuments()  [self] (querySnapshot, error) in
                // Check for errors.
                if let error = error 
                    print(error.localizedDescription)
                
                else  // if there are not errors.
                    for course in querySnapshot!.documents 
                        let courseInfo = course.data()
                        manageData(courseInfo)
                    
                
            
        
    // end retreiveData()
    
    private func manageData(_ courseInfo: [String : Any]) 
        var courseName: String = ""
        var students: [Any] = []
        var courseID: String = ""
        
        for (key, value) in courseInfo 
            if key == "Teacher" && value as! String == user!.uid 
                for (key, value) in courseInfo 
                    if key == "Course Name" 
                        courseName = value as! String
                    
                    else if key == "Course ID" 
                        courseID = value as! String
                    
                    else if key == "Students"
                        students = value as! Array<Any>
                    
                
                self.courses.append(CourseInfo(courseName: courseName, totalStudents: students.count, courseID: courseID))
            
        
        
     // end manageData()

CourseListView.swift

import SwiftUI

struct CourseListView: View 
    var thaCourse:[CourseInfo] = Course().courses
    
    var body: some View 
        List 
            ForEach(thaCourse)  course in
                CourseCell(course: course)
            
        
    


struct CourseCell: View 
    var course: CourseInfo
    
    var body: some View 
        VStack(alignment:.leading, spacing: 3) 
            
            Text(course.courseName)
                .font(.title2)
                .fontWeight(.semibold)
                .lineLimit(2)
                .minimumScaleFactor(0.5)
            
            Text("Total de alumnos: \(course.totalStudents)")
            
            Text("ID: \(course.courseID)")
        
    

【参考方案1】：

您需要在视图中将Course 类声明为@StateObject（或@ObservedObject）属性，然后通过该属性访问数组。你还需要获取你的数据，这里我在视图出现时使用onAppear

@StateObject var course: Course = Course()

var body: some View 
    List 
        ForEach(course.courses)  course in
            CourseCell(course: course)
        
    
    .onAppear 
        course.retreiveData()