In Swift how do I programmatically select a navigation link in a list

Question

In a Swift navigation split view once all of the data has been loaded from core data (indicated by the isLoading variable being equal to false) the Progress View stops being displayed but the detail view is now empty. What I would like have happen at this point is for the Summary view to be displayed. I think this would require programmatically setting the list selection to "Home". How do I need to modify my code to accomplish this? Below is the code.

struct ContentView: View {
    @State private var selection: String?
    @ObservedObject private var vooVM: VOOViewModel
    @ObservedObject private var vfiaxVM: VFIAXViewModel
    @ObservedObject private var prinVM: PrincipalViewModel
    init(vooVM: VOOViewModel, vfiaxVM: VFIAXViewModel, prinVM: PrincipalViewModel) {
        self.vooVM = vooVM
        self.vfiaxVM = vfiaxVM
        self.prinVM = prinVM
    }
    let myList = ["Home", "VOO Chart", "VOO List", "VFIAX Chart", "VFIAX List", "Principal Chart", "Principal List"]
    var body: some View {
        NavigationSplitView {
            List(myList, id: \.self, selection: $selection) { listItem in
                NavigationLink(value: listItem) {
                    Text(listItem)
                } // end navigation link
            } // end list
            .navigationSplitViewColumnWidth(250)
        } detail: {
            if vooVM.isloading == true || vfiaxVM.isloading == true || prinVM.isloading == true {
                Spacer()
                ProgressView()
                    .navigationSplitViewColumnWidth(950)
                Spacer()
            } else if selection == "Home" {
                Summary(vooVM: vooVM, vfiaxVM: vfiaxVM, prinVM: prinVM)
                    .navigationSplitViewColumnWidth(950)
            } else if selection == "VOO Chart" {
                LineChart(passedInArray: vooVM.values1)
                    .navigationSplitViewColumnWidth(950)
            } else {
                Text("Select an option in the list")
            }
            Spacer()
        }
        .frame(width: 1200,height: 900, alignment: .center)
    } // end body
} // end struct

`In Swift how do I programmatically select a navigation link in a list`, have a look at this doc, it shows you exactly how, `To navigate programmatically, introduce a state variable that tracks the items on a stack.` — workingdog support Ukraine, Nov 05 '22 at 23:13
To what document are you referring when you say look at this doc? — Chris, Nov 06 '22 at 18:56
Sorry my mistake, I forgot to include the link to the `NavigationLink` docs, https://developer.apple.com/documentation/swiftui/navigationlink about 1/3 from the top, it gives some example code. Note, you don't have to use `if vooVM.isloading == true ...`, just `if vooVM.isloading ...` is enough. — workingdog support Ukraine, Nov 06 '22 at 22:51

score 0 · Answer 1 · answered Nov 06 '22 at 20:18

0

After further reviewing my code including the if... else if... logic I realized that I only need to change one line in the code. If I set the selection to "Home" initially, once all of the isLoading variables are false the if... else if... logic will find selection = "Home" and in turn the Summary View will be shown automatically.

change: @State private var selection: String?
to:     @State private var selection: String = "Home"

answered Nov 06 '22 at 20:18

Chris

105
8

this does not seem to address the question you asked: `In Swift how do I programmatically select a navigation link in a list` – workingdog support Ukraine Nov 06 '22 at 22:57
I have read thru the doc and if gives a good example. What I do not understand is where/how to set the selection variable in ContentView once the data has loaded. Any ideas? Thank you for you input. – Chris Nov 07 '22 at 02:49

score 0 · Answer 2 · answered Nov 07 '22 at 20:06

Workingdog is correct. I had not really solved the problem. I have updated the code to include two onChange events that were added to the Navigation Link and the list now works programmaticaly.

@State private var selection: String?

.onChange(of: prinVM.isloading  && vooVM.isloading && vfiaxVM.isloading) { newValue in
    self.selection = "Home"
} // end on change
.onChange(of: selection) { [selection] newValue in
    if (selection == "Home" && newValue == "VOO Index Fund") {
        self.selection = "VOO Chart"
    } else if (selection == "VOO Chart" && newValue == "VOO Index Fund") {
        self.selection = "Home"
    } else if (selection == "VOO List" && newValue == "VFIAX Index Fund") {
        self.selection = "VFIAX Chart"
    } else if (selection == "VFIAX Chart" && newValue == "VFIAX Index Fund") {
        self.selection = "VOO List"
    } else if (selection == "VFIAX List" && newValue == "Principal Index Fund") {
        self.selection = "Principal Chart"
    } else if (selection == "Principal Chart" && newValue == "Principal Index Fund" ) {
         self.selection = "VFIAX List"
    } else {
   }
} // end on change

In Swift how do I programmatically select a navigation link in a list

2 Answers2