How to change @State property wrapper from nested view

Question

I'm wondering how I should change @State property wrapper showErrorAlert in view below

struct SettingsView: View {
@State private var shouldPresent = false
@State var showErrorAlert = false
var body: some View {
    VStack {
        Form {
            Text("Settings")
                .font(.title)
            Button("Import source data") {
                self.shouldPresent.toggle()
            }
            .sheet(isPresented: $shouldPresent) {
                DocumentPicker()
            }
            Button("Show error alert") {
                self.showErrorAlert.toggle()
            }
            .alert(isPresented: $showErrorAlert, content: {
                Alert(title: Text("Error"))
            })
        }
    }
}
}

from DocumentPicker struct code in case that reading of selected file fails.

struct DocumentPicker: UIViewControllerRepresentable {

func makeCoordinator() -> DocumentPicker.Coordinator {
    return DocumentPicker.Coordinator(parent: self)
}

func makeUIViewController(context: UIViewControllerRepresentableContext<DocumentPicker>) -> UIDocumentPickerViewController {
    let picker = UIDocumentPickerViewController(documentTypes: [String(kUTTypeJSON)], in: .import)
    picker.allowsMultipleSelection = false
    picker.delegate = context.coordinator
    return picker
}

func updateUIViewController(_ uiViewController: UIDocumentPickerViewController, context: UIViewControllerRepresentableContext<DocumentPicker>) {
}

class Coordinator: NSObject, UIDocumentPickerDelegate {

    var myParent: DocumentPicker
    init(parent: DocumentPicker) {
        myParent = parent
    }

    func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
        let fileURL = urls.first!
        do {
            let origFile = try String(contentsOf: fileURL)
            //File processing will be here
        } catch let error {
            print(error)
        }
    }
}
}

I mean how to set property wrapper value to true to show the alert. Should I rather use @ObservedObject or @EnvironmentObject instead? Thanks.

score 2 · Accepted Answer · answered Feb 06 '20 at 21:08

2

To change the wrapper value in your DocumentPicker struct you can define a @Binding variable and pass your value to it, this toggle your variable on your parent view, but before showing the alert you need to dismiss the DocumentPicker

answered Feb 06 '20 at 21:08

Mac3n

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If I declare @Binding var isPresented = false in DocumentPicker struct I get error "Argument labels '(wrappedValue:)' do not match any available overloads" – Dawy Feb 07 '20 at 20:25
There is no need to set value for your @Binding variable, you should just define `@Binding var isPresented: Bool` – Mac3n Feb 07 '20 at 20:26
Right. And how I could to set isPresented variable within func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) to true to make alert shown? Compiler says "Instance member 'isPresented' of type 'DocumentPicker' cannot be used on instance of nested type 'DocumentPicker.Coordinator'" if I try isPresented = true in do-catch. – Dawy Feb 07 '20 at 20:37
calling `myParent.isPresented = true` should work in a catch block – Mac3n Feb 07 '20 at 20:50

How to change @State property wrapper from nested view

1 Answers1