表单中的 SwiftUI 选择器不显示所选行

Question

我正在尝试使用一个选择器来显示当前选择了哪个选项。

试试下面的代码，它正确地选择了正确的选项，但选择器不显示选择了哪个选项：

import SwiftUI

struct ContentView: View {
@State var selectedIndex: Int = 0

let strings: [String] = {
    var strings: [String] = []
    for i in 0..<10 {
        strings.append("\(i)")
    }
    return strings
}()

var body: some View {
    NavigationView {
        VStack {
            Form {
                Picker(selection: $selectedIndex,
                       label: Text("Selected string: \(strings[selectedIndex])")) {
                    ForEach(0..<strings.count) {
                        Text(self.strings[$0]).tag($0)
                    }
                }
            }
        }
        .navigationBarTitle("Form Picker",
                            displayMode: NavigationBarItem.TitleDisplayMode.inline)
    }
}

}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

有谁知道可能有什么问题？使用 Xcode 11.1 和 iOS 13.1 观察到

Answer 1

我创建了一个简单的选择器，我称之为“ListPicker”，它应该符合要求。我已经编写了它，因此它在表单中运行良好；如果您在表单之外需要它，您将不得不修改它。如果您发现任何改进代码的方法，请添加评论；对于我们所有人来说，这仍然是一次学习经历。

// MARK: - LIST PICKER (PUBLIC)

struct ListPicker<Content: View>: View {
    @Binding var selectedItem: Int
    var label: () -> Content
    var data: [Any]

    var selectedLabel: String {
        selectedItem >= 0 ? "\(data[selectedItem])" : ""
    }

    var body: some View {
        NavigationLink(destination: ListPickerContent(selectedItem: self.$selectedItem, data: self.data)) {
            ListPickerLabel(label: self.label, value: "\(self.selectedLabel)")
        }
    }
}

// MARK: - INTERNAL

private struct ListPickerLabel<Content: View>: View {
    let label: () -> Content
    let value: String

    var body: some View {
        HStack(alignment: .center) {
            self.label()
            Spacer()
            Text(value)
                .padding(.leading, 8)
        }
    }
}

private struct ListPickerContentItem: View {
    let label: String
    let index: Int
    let isSelected: Bool
    var body: some View {
        HStack {
            Text(label)
            Spacer()
            if isSelected {
                Image(systemName: "checkmark")
                    .foregroundColor(.accentColor)
            }
        }.background(Color.white) // so the entire row is selectable
    }
}

private struct ListPickerContent: View {
    @Environment(\.presentationMode) var presentationMode
    @Binding var selectedItem: Int
    var data: [Any]
    var body: some View {
        List {
            ForEach(0..<data.count) { index in
                ListPickerContentItem(label: "\(self.data[index])", index: index, isSelected: index == self.selectedItem).onTapGesture {
                    self.selectedItem = index
                    self.presentationMode.wrappedValue.dismiss()
                }
            }
        }
    }
}

然后你可以像这样使用它：

@State var selectedCar: Int = 0
let cars = ["Jaguar", "Audi", "BMW", "Land Rover"]

Form {
    ListPicker(
        selectedItem: self.$selectedCar, 
        label: {
            Text("Cars")
        }, 
        data: self.cars
    )
}