将Swiftui选择器与课堂

Question

我一直在努力让选择器从数组中返回对象。我的印象是，我要做的就是将对象作为标签包括在内，而选择最终将作为该对象。显然不是。任何帮助将不胜感激。

我的实际应用使用从Coredata提取的信息。

该测试应用程序中的预期结果是将选择的选择显示了做出选择的项目的右侧。

import SwiftUI

class Choice: Identifiable, Hashable
{
    let id: UUID
    var name = ""
    
    init()
    {
        self.id = UUID()
    }
    
    init(_ name: String)
    {
        self.id = UUID()
        self.name = name
    }
    
    static func == (lhs: Choice, rhs: Choice) -> Bool
    {
        return lhs.name < rhs.name
    }
    
    func hash(into hasher: inout Hasher)
    {
        hasher.combine(name)
    }
    
}

class Stuff: Identifiable
{
    let id: UUID
    var title: String
    var choice: Choice?
    
    init(_ title: String)
    {
        self.id = UUID()
        self.title = title
    }
}

struct ContentView: View
{
    let items = [Stuff("ABC"), Stuff("XYZ")]
    let choices = [Choice("ONE"),Choice("Two"), Choice("Three)")]
    
    @State var choice: Choice?
    
    var body: some View
    {
        VStack
        {
            ForEach(items)
            { item in
                HStack
                {
                    Text(item.title)
                    Picker("Choice", selection: $choice)
                    {
                        ForEach(choices)
                        {
                            c in
                            Text(c.name).tag(c)
                        }
                    }
                }
            }
            Spacer()
            ForEach(items)
            {
                item in
                HStack
                {
                    Text(item.title)
                    Spacer()
                    if let c = item.choice
                    {
                        Text(c.name)
                    } else
                    {
                        Text("No choice")
                    }
                }
            }
        }
    }
}

Answer 1

选择和标签应按类型匹配，目前不匹配，因此

// give initial value (anyway first is by default)
@State var choice: Choice = Choice("ONE")  // << here !!

时还需要修复修复

static func == (lhs: Choice, rhs: Choice) -> Bool
{
    return lhs.name == rhs.name    // << here !!
}

在用Xcode 13.4 / ios 15.5进行测试

Answer 2

下面的建议肯定有所帮助，但正如指出的那样，有几个错误/假设使原始方法粗略。我通过创建一个单独的视图来展示每行/（列表项目）并将选择器分开，从而结合了建议并更改了策略。

import SwiftUI

struct Choice: Identifiable, Hashable
{
    let id: UUID
    var name = ""
    
    init()
    {
        self.id = UUID()
    }
    
    init(_ name: String)
    {
        self.id = UUID()
        self.name = name
    }
    
    static func == (lhs: Choice, rhs: Choice) -> Bool
    {
        return lhs.name == rhs.name
    }
    
    func hash(into hasher: inout Hasher)
    {
        hasher.combine(name)
    }
    
}

struct Stuff: Identifiable
{
    let id: UUID
    var title: String
    var choice: Choice?
    
    init(_ title: String)
    {
        self.id = UUID()
        self.title = title
    }
}

struct ContentView: View
{
    @State var items = [Stuff("ABC"), Stuff("XYZ")]
    
    @State var idx = 0
    
    var body: some View
    {
        VStack
        {
            ForEach($items)
            { $item in
                ItemLine(item: $item)
            }
            Spacer()
            ForEach(items)
            {
                item in
                HStack
                {
                    Text(item.title)
                    Spacer()
                    if let c = item.choice
                    {
                        Text(c.name)
                    } else
                    {
                        Text("No choice")
                    }
                }
            }.id(idx)
            Button("Refresh")
            {
                idx = idx + 1
            }
        }.padding()
    }
    
    struct ItemLine: View
    {
        @Binding var item: Stuff
        
        let choices = [Choice("One"),Choice("Two"), Choice("Three")]
        
        var body: some View
        {
            HStack
            {
                Text(item.title)
                Picker("Choice", selection: $item.choice)
                {
                    ForEach(choices)
                    {
                        c in
                        Text(c.name).tag(Optional(c))
                    }
                }
            }
        }
    }
}