How to maintain the selectedTextRange in a UITextView UIViewRepresentable, it should remain selected even after the focus shifts to another TextField

Question

I created this SwiftUI GrowingTextViewRepresentable, which represents a UITextView. I want to maintain the selectedTextRange even after the focus shifts to another TextField/TextView. To achieve this, I tried preserving it with a Binding. I save it in textViewDidEndEditing, expecting it to remain selected when the focus changes to another text field. I then set it again in updateUIView when the view loads. However, it's not working as expected. What am I doing wrong, or how can I achieve this?

FYI: GrowingTextView is just a UITextView subclass, which increases the height when multiline text changes.

GrowingTextViewRepresentable Code:

import UIKit
import SwiftUI
import GrowingTextView


struct GrowingTextViewRepresentable: UIViewRepresentable {
    
    
    let textView = GrowingTextView()
    var placeHolder: String = ""
    var customFont: UIFont = .systemFont(ofSize: 12)
    var placeHolderColor: UIColor = .grey
    var textColor: UIColor = .black
    
    @Binding var text: String
    @Binding var height: CGFloat
    @Binding var selectedText: String
    @Binding var selectedTextRange: UITextRange?
    
    
    func makeUIView(context: Context) -> GrowingTextView {
        textView.delegate = context.coordinator
        textView.font = customFont
        textView.placeholder = placeHolder
        textView.placeholderColor = placeHolderColor
        textView.textColor = textColor
        textView.backgroundColor = .clear
        textView.clipsToBounds = true
        return textView
    }
    
    func updateUIView(_ uiView: GrowingTextView, context: Context) {
        uiView.text = text
        
        if selectedTextRange != nil && uiView.selectedTextRange != selectedTextRange  {
            uiView.selectedTextRange = selectedTextRange
        }
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(text: $text, placeHolder: placeHolder, height: $height, selectedText: $selectedText, selectedTextRange: $selectedTextRange)
    }
    
    class Coordinator: NSObject, GrowingTextViewDelegate {
        
        @Binding var text: String
        var placeHolder: String
        @Binding var height: CGFloat
        @Binding var selectedText: String
        @Binding var selectedTextRange: UITextRange?
        
        private var tempSelectedBodyTextRange: UITextRange? = nil
        
        init(text: Binding<String>, placeHolder: String, height: Binding<CGFloat>, selectedText: Binding<String>, selectedTextRange: Binding<UITextRange?>) {
            self._text = text
            self.placeHolder = placeHolder
            self._height = height
            self._selectedText = selectedText
            self._selectedTextRange = selectedTextRange
        }
        
        func textViewDidChange(_ textView: UITextView) {
            // UIKit -> SwiftUI
            _text.wrappedValue = textView.text
        }
        
        func textViewDidChangeSelection(_ textView: UITextView) {
            // Fires off every time the user changes the selection.
            if let selectedText = textView.selectedText, let range = textView.selectedTextRange {
                DispatchQueue.main.async { [weak self] in
                    guard let self = self else { return }
                    self._selectedText.wrappedValue = selectedText
                    self._selectedTextRange.wrappedValue = range
                    self.tempSelectedBodyTextRange = range
                }
                //print(selectedText)
            }
        }
        
        func textViewDidChangeHeight(_ textView: GrowingTextView, height: CGFloat) {
            DispatchQueue.main.async {
                self.height = height
            }
        }
        
        func textViewDidEndEditing(_ textView: UITextView) {
            
            // Save the selected range when the text view ends editing
            if let range = tempSelectedBodyTextRange {
                DispatchQueue.main.async {
                    self._selectedTextRange.wrappedValue = range
                    textView.selectedTextRange = range
                }
            }
        }
    }
}

extension UITextView {
    var selectedText: String? {
        guard let selectedRange = selectedTextRange else { return nil }
        return text(in: selectedRange)
    }
}

How I'm using it:

import UIKit

struct MyView: View {
    
    @State private var body:String = ""
    @State private var selectedBodyText: String = ""
    @State private var selectedBodyTextRange: UITextRange? = nil
    @State private var heightOfBody: CGFloat = 0
    
    var body: some View {
        
        
        GrowingTextViewRepresentable(placeHolder: "write about...",
                                     text: body, height: $heightOfBody, selectedText: selectedBodyText, selectedTextRange: selectedBodyTextRange)
        .frame(height: heightOfBody)
        .frame(minHeight: 20)
        .onChange(of: viewModel.selectedBodyText, perform: { newValue in
            print("selectedBodyText: \(newValue)")
        })
    }
}

I attempted to retain the value in tempSelectedBodyTextRange and then reset it in textViewDidEndEditing, but it didn't work as expected.

Answer 1

makeUIView needs to init and return your GrowingTextView otherwise it will be lost, e.g.

func makeUIView(context: Context) -> GrowingTextView {
    let view = GrowingTextView()
    // or return context.coordinator.view where view is a lazy var

Coordinator cannot be init with any params or the params will be lost, it must be given the latest params in updateUIView, e.g.

func makeCoordinator() -> Coordinator {
    Coordinator()
}

func updateUIView(_ uiView: GrowingTextView, context: Context) {
   // update coordinator with any values/bindings that are different
   // update uiView with any values that are different