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添加选择器以更改Observable类中的数据

picker observable swiftui swift

Atharv Salokhe · 技术社区 · 8 月前

我试图使用选择器通过自定义结构更改存储在类中的值。我正在尝试制作一个列出课程名称和成绩的应用程序。拾取器位于一个名为HStack的文件夹中。我无法使用选择器更改特定元素(在本例中为grade)的值。我使用Observable类,因为我有多个视图需要访问该类。

这是我的一些代码,

struct courseItem: Identifiable{
    var id = UUID()
    let name: String
    let grade: String
}
@Observable
class Courses{
    var items = [courseItem]()
}
struct ContentView: View{
    @State private var courses = Courses()
    let grades = ["A", "B", "C"]
    var body: some View{
        List{
            ForEach(courses.items){ item in 
                HStack{
                    Text(item.name)
                    Spacer()
                    Picker("Grade", selection: item.grade){
                        ForEach(grades, id: \.self){
                            Text($0)
                        }
                    }
                }
            }
     
        }
    }
}

我知道 item.grade 应该是有约束力的,但我这样做时出错了。现在我收到一个错误,说编译器无法在合理的时间内对表达式进行类型检查。任何帮助都将不胜感激。

1 回复 | 直到 8 月前

workingdog support Ukraine 8 月前

尝试使用绑定的方法 $ 如示例代码所示, ...to change the value of a particular element, (in this example, grade)

struct courseItem: Identifiable {
    let id = UUID()  // <--- here
    var name: String
    var grade: String  // <--- here
}

@Observable class Courses {
    // <--- for testing
    var items: [courseItem] = [courseItem(name: "name-1", grade: "A"),
                               courseItem(name: "name-2", grade: "B"),
                               courseItem(name: "name-3", grade: "C")
    ]
}

struct ContentView: View {
    @State private var courses = Courses()
    
    let grades = ["A", "B", "C"]
    
    var body: some View{
        List{
            ForEach($courses.items){ $item in   // <--- here
                HStack{
                    Text(item.name)
                    Spacer()
                    Picker("Grade", selection: $item.grade) {  // <--- here
                        ForEach(grades, id: \.self) {
                            Text($0)
                        }
                    }
                }
            }
        }
    }
}

如果你想通过 courses 对于其他视图,您可以使用 @Bindable var courses: Courses 以允许编辑所需的属性,例如:

struct ContentView: View {
    @State private var courses = Courses() // <--- here, only one source of truth data

    var body: some View {
        TestOtherView(courses: courses) // <--- here
    }
}

struct TestOtherView: View {
    @Bindable var courses: Courses  // <--- here
    
    let grades = ["A", "B", "C"]
    
    var body: some View {
        List{
            ForEach($courses.items){ $item in   // <--- here
                HStack{
                    Text(item.name)
                    Spacer()
                    Picker("Grade", selection: $item.grade) {  // <--- here
                        ForEach(grades, id: \.self) {
                            Text($0)
                        }
                    }
                }
            }
        }
    }
}

注意,如果你想通过 课程 对于许多其他观点,考虑使用 @Environment(Courses.self) private var courses 请参阅以下文档 Managing model data in your app .

例如:

struct ContentView: View{
    @State private var courses = Courses()

    var body: some View{
        TestOtherView()
            .environment(courses) // <--- here
    }
}

struct TestOtherView: View{
    @Environment(Courses.self) private var courses  // <--- here
    let grades = ["A", "B", "C"]
    
    var body: some View{
        @Bindable var courses = courses  // <--- here
        List{
            ForEach($courses.items){ $item in   // <--- here
                HStack{
                    Text(item.name)
                    Spacer()
                    Picker("Grade", selection: $item.grade) {  // <--- here
                        ForEach(grades, id: \.self) {
                            Text($0)
                        }
                    }
                }
            }
        }
    }
}