SwiftUI, selecting a row in a List programmatically - list

Question

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

Answer 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)
}
}

Answer 2

thanks to Introspect： https://github.com/siteline/SwiftUI-Introspect
handle iPad Sidebar unable to set default row & make selected style visible in initial:
Example:
struct TempData: Identifiable {
var id: Int
var title: String
}
struct TempView: View {
// handle selection nil: when detail view pushs view, selection == nil
#State private var keepSelection: Int = 2
// bind list selected row
#State private var selection: Int? = 2 // set default row
private var dataArr: [TempData] = [TempData(id: 1, title: "one"),
TempData(id: 2, title: "two"),
TempData(id: 3, title: "three")]
var body: some View {
List(selection: $selection) {
ForEach(dataArr.indices) { index in
NavigationLink(destination: Text("\(dataArr[index].title)").onAppear {
keepSelection = (selection != nil ? selection! : keepSelection)
}, tag: dataArr[index].id, selection: $selection) {
HStack {
Text("\(dataArr[index].title)")
}
}
.introspectTableViewCell(customize: { cell in
// import Introspect
// https://github.com/siteline/SwiftUI-Introspect
cell.selectionStyle = .none
cell.backgroundColor = .systemGroupedBackground
})
.tag(dataArr[index].id) // or use enum
.listRowBackground(keepSelection == dataArr[index].id ? Color.accentColor.cornerRadius(10.0): Color(UIColor.systemGroupedBackground).cornerRadius(10))
}
}
}
}

Answer 3

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)
}