快速选择器不选择项目

Question

我想在分段选择器中显示一小部分项目。我正在传递所选项目（默认情况下为 0）。选择器显示，但未选择任何项目，并且选择器对点击无响应（在模拟器中）。我有一个非常相似的选择器，它使用百分比值，并且可以正常工作。我猜这个问题与我传递给 ForEach 循环的闭包有关，但我不清楚我应该使用什么语法，如果这确实是问题。

代码如下：

@State private var originalUnit = 0
let sourceUnits = ["meters","kilometers","feet","yards","miles"]

var body: some View {
   NavigationView {
      Form {
         Section {
             Picker("Unit", selection $originalUnit) {
                 ForEach(sourceUnits, id: \.self {
                     Text($0)
                 }
             } .pickerStyle(.segmented)
         } header: {
             Text("Choose Unit")
         }
      }  .navigationTitle("MyApp")
    }
  }
}

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

对此的任何见解将不胜感激。提前致谢！

Answer 1

您的originalUnit (Int) 和sourceUnits (String) 之间存在类型不匹配。您的选择需要与类型匹配。

struct ContentView: View {
    @State private var originalUnit = "meters" //<-- Here
    let sourceUnits = ["meters","kilometers","feet","yards","miles"]
    
    var body: some View {
        NavigationView {
            Form {
                Section {
                    Picker("Unit", selection: $originalUnit) {
                        ForEach(sourceUnits, id: \.self) {
                            Text($0)
                        }
                    } .pickerStyle(.segmented)
                } header: {
                    Text("Choose Unit")
                }
            }  .navigationTitle("MyApp")
        }
    }
}

如果出于某种原因，您确实需要 originalUnit 成为 Int，则可以使用 enumerated（通常不是 ForEach 中大型集合的最有效方法，但这无关紧要对于这么小的东西），以便id 是索引并匹配originalUnit 的类型（Int）：

struct ContentView: View {
    @State private var originalUnit = 0
    let sourceUnits = ["meters","kilometers","feet","yards","miles"]
    
    var body: some View {
        NavigationView {
            Form {
                Section {
                    Picker("Unit", selection: $originalUnit) {
                        ForEach(Array(sourceUnits.enumerated()), id: \.0) { //<-- .0 is the index (Int)
                            Text($0.1) //<-- .1 is the original item String
                        }
                    } .pickerStyle(.segmented)
                } header: {
                    Text("Choose Unit")
                }
            }  .navigationTitle("MyApp")
        }
    }
}

Answer 2

您可以为您的选择器行设置tag。标签是任何hashable 类型。 请参考此代码使用任何类型的对象进行选择

struct TestView: View {
    @StateObject var viewModel = TestViewModel()
    var body: some View {
        VStack {
            Text(viewModel.selectedItem.title)
            Picker("Select item", selection: $viewModel.selectedItem) {
                ForEach(viewModel.items) { makeRowForItem($0) }
            }
        }
    }
    
    @ViewBuilder
    func makeRowForItem(_ item: Item) -> some View {
        Text(item.title).tag(item)
    }
}

struct Item: Identifiable, Hashable {
    var id = UUID().uuidString
    var title = "Untitled"
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }
}

class TestViewModel: ObservableObject {
    @Published var selectedItem: Item
    @Published var items: [Item]
    
    init() {
        let list = (1..<10).map { Item(title: "Untitled \($0)") }
        items = list
        selectedItem = list.first!
    }
}