SwiftUI, selecting a row in a List programmatically

问题

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)
  }
}

trying to make the List selectable like this:

List(selection: $selection)

does not compile.
Compiler complains: Unable to infer complex closure return type; add explicit type to disambiguate

回答1:

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)
  }
}

回答2:

It won't compile because the tags are not unique. You are setting tag 1 twice. It can not identify the value, thats why List(selection: $selection) does not work either.

 List() {
      //List(selection: $selection)  {.  // should compile now
        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)
 }

来源：https://stackoverflow.com/questions/61838352/swiftui-selecting-a-row-in-a-list-programmatically

标签

list

macos

swiftui