Create UIViewRepresentable / UITextView for iOS post title editor

iOS/PostEditor/PostTitleTextView.swift

@@ -1,20 +1,95 @@
-//
-//  PostTitleTextView.swift
-//  WriteFreely-MultiPlatform (iOS)
-//
-//  Created by Angelo Stavrow on 2020-10-27.
-//
+// Based on https://lostmoa.com/blog/DynamicHeightForTextFieldInSwiftUI/
+// and https://stackoverflow.com/a/56508132/1234545
 
 import SwiftUI
 
-struct PostTitleTextView: View {
-    var body: some View {
-        Text(/*@START_MENU_TOKEN@*/"Hello, World!"/*@END_MENU_TOKEN@*/)
+class Coordinator: NSObject, UITextViewDelegate, NSLayoutManagerDelegate {
+    @Binding var text: String
+    @Binding var isFirstResponder: Bool
+    var didBecomeFirstResponder: Bool = false
+    var postTitleTextView: PostTitleTextView
+
+    weak var textView: UITextView?
+
+    init(_ textView: PostTitleTextView, text: Binding<String>, isFirstResponder: Binding<Bool>) {
+        self.postTitleTextView = textView
+        _text = text
+        _isFirstResponder = isFirstResponder
+    }
+
+    func textViewDidChangeSelection(_ textView: UITextView) {
+        DispatchQueue.main.async {
+            self.postTitleTextView.text = textView.text ?? ""
+        }
+    }
+
+    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
+        if (text == "\n") {
+            self.isFirstResponder.toggle()
+            return false
+        }
+        return true
+    }
+
+    func layoutManager(
+        _ layoutManager: NSLayoutManager,
+        didCompleteLayoutFor textContainer: NSTextContainer?,
+        atEnd layoutFinishedFlag: Bool
+    ) {
+        DispatchQueue.main.async {
+            guard let view = self.textView else {
+                return
+            }
+            let size = view.sizeThatFits(view.bounds.size)
+            if self.postTitleTextView.height != size.height {
+                self.postTitleTextView.height = size.height
+            }
+        }
     }
 }
 
-struct PostTitleTextView_Previews: PreviewProvider {
-    static var previews: some View {
-        PostTitleTextView()
+struct PostTitleTextView: UIViewRepresentable {
+    @Binding var text: String
+    @Binding var textStyle: UIFont
+    @Binding var height: CGFloat
+    @Binding var isFirstResponder: Bool
+
+    func makeUIView(context: UIViewRepresentableContext<PostTitleTextView>) -> UITextView {
+        let textView = UITextView()
+
+        textView.isEditable = true
+        textView.isUserInteractionEnabled = true
+        textView.isScrollEnabled = true
+        textView.alwaysBounceVertical = false
+
+        context.coordinator.textView = textView
+        textView.delegate = context.coordinator
+        textView.layoutManager.delegate = context.coordinator
+
+        let font = textStyle
+        let fontMetrics = UIFontMetrics(forTextStyle: .largeTitle)
+        textView.font = fontMetrics.scaledFont(for: font)
+
+        textView.backgroundColor = UIColor.clear
+
+        return textView
+    }
+
+    func makeCoordinator() -> Coordinator {
+        return Coordinator(self, text: $text, isFirstResponder: $isFirstResponder)
+    }
+
+    func updateUIView(_ uiView: UITextView, context: UIViewRepresentableContext<PostTitleTextView>) {
+        uiView.text = text
+
+        let font = textStyle
+        let fontMetrics = UIFontMetrics(forTextStyle: .largeTitle)
+        uiView.font = fontMetrics.scaledFont(for: font)
+
+        // We don't want the text field to become first responder every time SwiftUI refreshes the view.
+        if isFirstResponder && !context.coordinator.didBecomeFirstResponder {
+            uiView.becomeFirstResponder()
+            context.coordinator.didBecomeFirstResponder = true
+        }
     }
 }