SwiftUI，以编程方式在列表中选择一行 [英] SwiftUI, selecting a row in a List programmatically

问题描述

我想以编程方式设置列表中的选定行.
在下面的示例中，通过2个按钮.

I want to set the selected row in a List programmatically.
In my example below via 2 Buttons.

struct ContentView: View {

  @State private var selection = 2

  var body: some View {
    VStack {
      List() {
      //List(selection: $selection)  {.  // does not compile
        Text("Line 0").tag(1)
        Text("Line 1").tag(1)
        Text("Line 2").tag(2)
        Text("Line 3").tag(3)
        Text("Line 4").tag(4)
        Text("Line 5").tag(5)
      }
      .listStyle(SidebarListStyle())
      Text("Selected Item :\(self.selection)")
      HStack {
        Button(action: {if (self.selection < 5 ) { self.selection += 1 }} ) {Text("⬇︎")}
        Button(action: {if (self.selection > 0 ) { self.selection -= 1 }} ) {Text("⬆︎")}
      }
    }
    .frame(maxWidth: .infinity, maxHeight: .infinity)
  }
}

试图使列表像这样可选:

trying to make the List selectable like this:

List(selection: $selection)  

无法编译.
编译器抱怨:无法推断复杂的闭包返回类型；添加显式类型以消除歧义

推荐答案

选择类型必须是可选的.查找下面的固定代码.

Selection type must be optional. Find below fixed code.

struct TestListSelectionOnAction: View {

  @State private var selection: Int? = 2 // optional !!

  var body: some View {
    VStack {
      List(selection: $selection)  {
        Text("Line 0").tag(0)
        Text("Line 1").tag(1)
        Text("Line 2").tag(2)
        Text("Line 3").tag(3)
        Text("Line 4").tag(4)
        Text("Line 5").tag(5)
      }
      .listStyle(SidebarListStyle())
      Text("Selected Item :\(self.selection ?? -1)")
      HStack {
        Button(action: {
            if (self.selection! < 5 ) { self.selection! += 1 }} ) {Text("⬇︎")}
        Button(action: {
            if (self.selection! > 0 ) { self.selection! -= 1 }} ) {Text("⬆︎")}
      }
    }
    .frame(maxWidth: .infinity, maxHeight: .infinity)
  }
}

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