SwiftUI - 如何将数据附加到嵌套结构？

Question

我有一个连接到结构的学生类 - 详细信息。其中有一个嵌套结构 - 主题。我知道如何附加到普通结构或类，但我在尝试附加到嵌套结构时遇到了困难。我所拥有的是一个表格，其中询问学生的姓名和科目数量，之后他们必须输入科目名称和等级。然后，按 Toolbar items/NavigationBarItems 中的保存按钮。

class Students: ObservableObject {
    @Published var details = [Details]()
}

struct Details: Identifiable {
    let id = UUID()
    let name: String
    
    struct Subjects: Identifiable {
        let id = UUID()
        let name: String
        let grade: String
    }
    
    let subjects: [Subjects]
}

视图类：

import SwiftUI

struct TestStudentView: View {
    @StateObject var students = Students()
    @State private var name = ""
    @State private var numberOfSubjects = ""
    @State private var subject = [String](repeating: "", count: 10)
    @State private var grade = [String](repeating: "", count: 10)
    @State private var details = [Details.Subjects]()
    var body: some View {
        NavigationView {
            Group {
                Form {
                    Section(header: Text("Student details")) {
                        TextField("Name", text: $name)
                        TextField("Number of subjects", text: $numberOfSubjects)
                    }
                    
                    let count = Int(numberOfSubjects) ?? 0
                    Text("Count: \(count)")
                    Section(header: Text("Subject grades")) {
                        if count>0 && count<10 {
                            ForEach(0 ..< count) { number in
                                TextField("Subject", text: $subject[number])
                                TextField("Grade", text: $grade[number])
                            }
                        }
                    }
                }
                VStack {
                    ForEach(students.details) { student in
                        Text(student.name)
                        ForEach(student.subjects) { subject in
                            HStack {
                                Text("Subject: \(subject.name)")
                                Text("Grade: \(subject.grade)")
                            }
                        }
                    }
                }
            }
            .navigationTitle("Student grades")
            .navigationBarItems(trailing:
                    Button(action: {
                        //let details = Details(name: name, subjects: [Details.Subjects(name: "Physics", grade: "A"), Details.Subjects(name: "Computer Science", grade: "A*")])
                        //students.details.append(details)
                        //^Above to append
                    }, label: {
                    Text("Save")
                })
            )
        }
    }
}

我尝试创建一个 [Subjects] 类型的变量，但在输入文本字段值后不允许我附加到它，它给了我错误：“类型 '()' 不能符合 'View';只有结构/枚举/类类型可以符合协议”（这是有道理的，因为它需要一个按钮）。一旦使用 ForEach 按下保存按钮，我也尝试过附加它，但这也会给我同样的错误。

Answer 1

我认为您希望模型更改由您的 Students 班级负责。尝试向Students 添加一个公共方法并从您的视图中调用它，如下所示：

class Students: ObservableObject {
    @Published var details = [Details]()
  
  public func addDetails(_ details : Details) {
    details.append(details)
  }
}

然后在视图中的按钮操作中，将students.details.append(details) 替换为对此方法的调用：

let details = Details(name: name, subjects: [Details.Subjects(name: "Physics", grade: "A"), Details.Subjects(name: "Computer Science", grade: "A*")])
students.details.append(details)

这就是你想要做的吗？

Answer 2

您的视图试图为单个视图做太多事情。您尝试在单个视图中添加学生和成绩。 Asperi 的答案是正确的。但是，您的错误表明您的代码有其他问题。尝试在隔离环境中运行下面的代码，它应该可以正常工作。 现在我只是为每个成绩添加了一个保存按钮，它将始终将成绩添加到第一个学生。

import SwiftUI

class Students: ObservableObject {
    @Published var details = [Details]()
}

struct Details: Identifiable {
    let id = UUID()
    let name: String
    
    struct Subjects: Identifiable {
        let id = UUID()
        let name: String
        let grade: String
    }
    
    var subjects: [Subjects]
}

struct TestStudentView: View {
    @StateObject var students = Students()
    @State private var name = ""
    @State private var numberOfSubjects = ""
    @State private var subject = [String](repeating: "", count: 10)
    @State private var grade = [String](repeating: "", count: 10)
    @State private var details = [Details.Subjects]()
    var body: some View {
        NavigationView {
            Group {
                Form {
                    Section(header: Text("Student details")) {
                        TextField("Name", text: $name)
                        TextField("Number of subjects", text: $numberOfSubjects)
                    }
                    
                    let count = Int(numberOfSubjects) ?? 0
                    Text("Count: \(count)")
                    Section(header: Text("Subject grades")) {
                        if count>0 && count<10 {
                            ForEach(0 ..< count) { number in
                                TextField("Subject", text: $subject[number])
                                TextField("Grade", text: $grade[number])
                                Button(action: {
                                    if students.details.count > 0 {
                                        var test = students.details[0]
                                        students.details[0].subjects.append(Details.Subjects(name: subject[number], grade: grade[number]))
                                    }
                                }) {
                                    Text("Save")
                                }
                            }
                        }
                    }
                }
                VStack {
                    ForEach(students.details) { student in
                        Text(student.name)
                        ForEach(student.subjects) { subject in
                            HStack {
                                Text("Subject: \(subject.name)")
                                Text("Grade: \(subject.grade)")
                            }
                        }
                    }
                }
            }
            .navigationTitle("Student grades")
            .navigationBarItems(trailing:
                    Button(action: {
                        let details = Details(name: name, subjects: [Details.Subjects(name: "Physics", grade: "A"), Details.Subjects(name: "Computer Science", grade: "A*")])
                        students.details.append(details)
                        //^Above to append
                    }, label: {
                    Text("Save")
                })
            )
        }
    }
}