swiftui-picker不显示选定的值

Question

初始位置：从数据库中填充两个选择器，其中第二个取决于第一个。我遵循此从上一个挑选器-CoreData/swiftui picker值示例，并且效果很好。 只有一个问题：第二个选择器未显示所选值。

    @State var courtSelected = 0
    @State var judgeSelected = 0

HStack{
    Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
        ForEach(0..<courts.count){ court in
            Text("\(courts[court].name ?? "Unknown")")
        }
    }
}
HStack {
    Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
        ForEach(Array(courts[courtSelected].courtsJudges! as! Set<Judges>), id: \.self) { judge in
            Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
        }
    }
}

仅差异：

1. 从NSSET到数组的修改
2. 我必须更改@binding var judgeselectected：int to @state，因为否则我必须将选择从App sctruct开始的参数选择作为参数。

在标签中打印$ judgessel的$ judgesselect示出了此VAR永远不会更改。

Answer 1

您的选择和演示文稿的类型有所不同，因此请添加标签：

Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
    ForEach(0..<courts.count){ court in
        Text("\(courts[court].name ?? "Unknown")").tag(court)  // << here !!
    }
}

第二个Picker Presents对象，因此选择也应该是一个对象，例如

@State var judgeSelected: Judges? = nil

接下来显示类似的情况，因此应有用 https://stackoverflow.com/a/a/68815871/12299030

Answer 2

尝试这样的事情：

    HStack{
        Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
            ForEach(0..<courts.count){ court in
                Text("\(courts[court].name ?? "Unknown")")
            }
        }
    }
    HStack {
        Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
            // -- here
            ForEach(Array(Set(courts[courtSelected].courtsJudges!)), id: \.self) { judge in  
                Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
            }
        }.id(UUID())   // <-- here
    }
}

还请注意第二个使用 set 的的。 PS，请勿使用强制解开，即。您的代码中没有！。

edit-1：为了避免使用arrayliteral的错误，请尝试以下：

    HStack {
        Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
            if let theJudges = courts[courtSelected].courtsJudges {
                ForEach(Array(Set(theJudges)), id: \.self) { judge in
                    Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
                }
            }
        }.id(UUID())
    }

edit-2：

这是我的测试代码，允许第二个选择器
取决于第一个选择器。我同时使用了id标记和标签
必须匹配选择类型。

由于您没有显示法院和法官的结构代码，
我为这些创建了一些示例结构。
您将必须调整代码以适合您的结构。

使用 struct struct的id在第二个挑选器中的tag中使用。
但是，还有其他方法可以使用int标签，例如使用数组索引，例如：

struct Judge: Identifiable, Hashable {
    var id: Int
    var gender: String?
    var name: String?
    var title: String?
}

struct Court: Identifiable, Hashable {
    var id: Int
    var name: String?
    var courtsJudges: [Judge]?
}

struct ContentView: View {
    @State var courtSelected = 0
    @State var judgeSelected = 0
    
    @State var courts: [Court] = [
        Court(id: 0, name: "one",
              courtsJudges: [
                Judge(id: 0, gender: "Male", name: "name1", title: "title1"),
                Judge(id: 1, gender: "Male", name: "name2", title: "title2"),
                Judge(id: 2, gender: "Male", name: "name3", title: "title3")
              ]),
        Court(id: 1, name: "two",
              courtsJudges: [
                Judge(id: 3, gender: "Female", name: "name7", title: "title7"),
                Judge(id: 4, gender: "Female", name: "name8", title: "title8"),
                Judge(id: 5, gender: "Female", name: "name9", title: "title9")
              ])
    ]

    var body: some View {
        VStack (spacing: 77) {
            HStack{
                Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
                    ForEach(0..<courts.count) { court in
                        Text("\(courts[court].name ?? "Unknown")").tag(court)
                    }
                }
            }
            HStack {
                Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
                    if let theJudges = courts[courtSelected].courtsJudges {
                        ForEach(Array(Set(theJudges))) { judge in
                            Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
                                .tag(judge.id)
                        }
                    }
                }.id(UUID())
            }
        }.padding()
    }
}

替代：：

 HStack {
     Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
         if let theJudges = courts[courtSelected].courtsJudges, let arr = Array(Set(theJudges)) {
             ForEach(arr.indices, id: \.self) { index in
                 Text("\(arr[index].gender ?? "") \(arr[index].title ?? "") \(arr[index].name ?? "")")
                     .tag(index)
             }
         }
     }.id(UUID())
 }

Answer 3

首先：感谢迄今为止的所有大力帮助。

直到现在将所有内容都结合在一起。

以下代码会创建一个选择器，但未显示选择。更改为放射线，您无法选择任何东西。

这是我的编辑代码

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Courts.name, ascending: true)],
        animation: .default
    )
    private var courts: FetchedResults<Courts>
    
    @State var courtSelected = 0
    @State var judgeSelected = 0
    
    var body: some View {
        HStack{
            Picker(selection: $courtSelected, label: Text("Gericht")){
                ForEach(0..<courts.count){ court in
                    Text("\(courts[court].name ?? "Unknown")").tag(court)
                }
            }
        }
        HStack {
            Picker(selection: $judgeSelected, label: Text("Richter \(judgeSelected)")){
                ForEach(Array(courts[courtSelected].courtsJudges as! Set<Judges>), id: \.self) { judge in
                    Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")").tag(judge)
                }
            }.id(UUID())
        }
    }
}

下一个代码仍然会导致错误

HStack {
    Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
        if let theJudges = courts[courtSelected].courtsJudges {
            ForEach(Array(Set(theJudges)), id: \.self) { judge in
                Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
            }
        }
    }.id(UUID())
}

net/3yq36.jpg“ rel =“ nofollow noreferrer 要去其他任何地方，因为一开始就没有显示任何东西，并且收音机是灰色的。

是，因为选择器2取决于选择器1，并且当选择了Picker 1中的值时会更改？

这全都用于XCode 13.4.1上的MacOS

Answer 4

我创建了一个具有核心数据的完整新项目，添加了两个实体（法院和法官），每个实体都有两个属性（ID和名称）。

然后我只做出了这个观点：

import SwiftUI
import CoreData

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Courts.name, ascending: true)],
        animation: .default
    )
    private var courts: FetchedResults<Courts>
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Judges.name, ascending: true)],
        animation: .default
    )
    private var judges: FetchedResults<Judges>
    
    @State var courtSelected = 0
    @State var judgeSelected = 0
    
    var body: some View {
        if(courts.count > 0) {
            HStack{
                Picker(selection: $courtSelected, label: Text("Gericht")){
                    ForEach(0..<courts.count){ court in
                        Text("\(courts[court].name ?? "Unknown")").tag(court)
                    }
                }
            }
            HStack {
                Picker(selection: $judgeSelected, label: Text("Richter \(judgeSelected)")){
                    ForEach(Array(courts[courtSelected].courtsJudges as! Set<Judges>), id: \.self) { judge in
                        Text("\(judge.name ?? "")").tag(judge)
                    }
                }.id(UUID())
            }
            HStack {
                Button("neue Gerichte") {
                    addItem()
                    addJudges()
                }
            }
        }
    }
    
    private func addItem() {
        for id in 0..<3 {
            let newItem = Courts(context: viewContext)
            newItem.id = UUID()
            newItem.name = "Gericht Nr. \(id)"
            
            
            do {
                try viewContext.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nsError = error as NSError
                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
            }
        }
        
    }
    
    
    private func addJudges() {
        for cd in 0..<courts.count {
            for jd  in 0..<3 {
                let newJudge = Judges(context: viewContext)
                newJudge.id = UUID()
                newJudge.name = "Richter \(jd) am Gericht \(courts[cd].name)"
                newJudge.judgesCourts = courts[cd]
                
                try? viewContext.save()
            }
        }
    }
    
}

结果：两个采摘者都可以，第一个ist还可以，第二个显示正确的法官，但它们不是“可选”的。