PR Feedback. Adopt similar behavior in AttachmentTextView

Author: michelle-signal

Signal/src/ViewControllers/ConversationView/ConversationInputTextView.swift

@@ -184,7 +184,7 @@ class ConversationInputTextView: MentionTextView {
 
     override func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
         textIsChanging = true
-        return true
+        return super.textView(self, shouldChangeTextIn: range, replacementText: text)
     }
 
     override func textViewDidChange(_ textView: UITextView) {

SignalMessaging/ViewControllers/AttachmentApproval/AttachmentTextView.swift

@@ -6,11 +6,36 @@ import Foundation
 import UIKit
 
 class AttachmentTextView: MentionTextView {
-    // When creating new lines, contentOffset is animated, but because
-    // we are simultaneously resizing the text view, this can cause the
-    // text in the textview to be "too high" in the text view.
-    // Solution is to disable animation for setting content offset.
+
+    private var textIsChanging = false
+
+    override func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
+        textIsChanging = true
+        return super.textView(self, shouldChangeTextIn: range, replacementText: text)
+    }
+
+    override func textViewDidChange(_ textView: UITextView) {
+        super.textViewDidChange(textView)
+        textIsChanging = false
+    }
+
     override func setContentOffset(_ contentOffset: CGPoint, animated: Bool) {
-        super.setContentOffset(contentOffset, animated: false)
+        // When creating new lines, contentOffset is animated, but because because
+        // we are simultaneously resizing the text view, on pre-iOS 13 this can
+        // cause the text in the textview to be "too high" in the text view.
+        // Solution is to disable animation for setting content offset between
+        // -textViewShouldChange... and -textViewDidChange.
+        //
+        // We can't unilaterally disable *all* animated scrolling because that breaks
+        // manipulation of the cursor in scrollable text. Animation is required to
+        // slow the text view scrolling down to human scale when the cursor reaches
+        // the top or bottom edge.
+        let shouldAnimate: Bool
+        if #available(iOS 13, *) {
+            shouldAnimate = animated
+        } else {
+            shouldAnimate = animated && !textIsChanging
+        }
+        super.setContentOffset(contentOffset, animated: shouldAnimate)
     }
 }