Scroll attachment description views to ensure caret is always visible

Tusker.xcodeproj/project.pbxproj

@@ -214,6 +214,7 @@
 		D6A4DCCC2553667800D9DE31 /* FastAccountSwitcherViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A4DCCA2553667800D9DE31 /* FastAccountSwitcherViewController.swift */; };
 		D6A4DCCD2553667800D9DE31 /* FastAccountSwitcherViewController.xib in Resources */ = {isa = PBXBuildFile; fileRef = D6A4DCCB2553667800D9DE31 /* FastAccountSwitcherViewController.xib */; };
 		D6A4DCE525537C7A00D9DE31 /* FastSwitchingAccountView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A4DCE425537C7A00D9DE31 /* FastSwitchingAccountView.swift */; };
+		D6A57408255C53EC00674551 /* ComposeTextViewCaretScrolling.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A57407255C53EC00674551 /* ComposeTextViewCaretScrolling.swift */; };
 		D6A5BB2B23BAEF61003BF21D /* APIMocks.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A5BB2A23BAEF61003BF21D /* APIMocks.swift */; };
 		D6A5BB2D23BBA9C4003BF21D /* MyProfileTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A5BB2C23BBA9C4003BF21D /* MyProfileTests.swift */; };
 		D6A5BB2F23BBAC97003BF21D /* DelegatingResponse.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A5BB2E23BBAC97003BF21D /* DelegatingResponse.swift */; };
@@ -562,6 +563,7 @@
 		D6A4DCCA2553667800D9DE31 /* FastAccountSwitcherViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FastAccountSwitcherViewController.swift; sourceTree = "<group>"; };
 		D6A4DCCB2553667800D9DE31 /* FastAccountSwitcherViewController.xib */ = {isa = PBXFileReference; lastKnownFileType = file.xib; path = FastAccountSwitcherViewController.xib; sourceTree = "<group>"; };
 		D6A4DCE425537C7A00D9DE31 /* FastSwitchingAccountView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FastSwitchingAccountView.swift; sourceTree = "<group>"; };
+		D6A57407255C53EC00674551 /* ComposeTextViewCaretScrolling.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ComposeTextViewCaretScrolling.swift; sourceTree = "<group>"; };
 		D6A5BB2A23BAEF61003BF21D /* APIMocks.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = APIMocks.swift; sourceTree = "<group>"; };
 		D6A5BB2C23BBA9C4003BF21D /* MyProfileTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MyProfileTests.swift; sourceTree = "<group>"; };
 		D6A5BB2E23BBAC97003BF21D /* DelegatingResponse.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DelegatingResponse.swift; sourceTree = "<group>"; };
@@ -1027,6 +1029,7 @@
 				D677284724ECBCB100C732D3 /* ComposeView.swift */,
 				D677284924ECBDF400C732D3 /* ComposeCurrentAccount.swift */,
 				D677284B24ECBE9100C732D3 /* ComposeAvatarImageView.swift */,
+				D6A57407255C53EC00674551 /* ComposeTextViewCaretScrolling.swift */,
 				D62275A924F1E01C00B82A16 /* ComposeTextView.swift */,
 				D6C99FCA24FADC91005C74D3 /* MainComposeTextView.swift */,
 				D622757324EDF1CD00B82A16 /* ComposeAttachmentsList.swift */,
@@ -1861,6 +1864,7 @@
 				D60E2F2E244248BF005F8713 /* MastodonCachePersistentStore.swift in Sources */,
 				D620483623D38075008A63EF /* ContentTextView.swift in Sources */,
 				D6F2E965249E8BFD005846BB /* CrashReporterViewController.swift in Sources */,
+				D6A57408255C53EC00674551 /* ComposeTextViewCaretScrolling.swift in Sources */,
 				D6CA6A94249FADE700AD45C1 /* GalleryPlayerViewController.swift in Sources */,
 				D6A3BC802321B7E600FD64D5 /* FollowNotificationGroupTableViewCell.swift in Sources */,
 				D627944D23A9A03D00D38C68 /* ListTimelineViewController.swift in Sources */,

Tusker/Screens/Compose/ComposeAttachmentsList.swift

@@ -112,6 +112,7 @@ struct ComposeAttachmentsList: View {
         let proxy = UITableView.appearance(whenContainedInInstancesOf: [ComposeHostingController.self])
         // enable drag and drop to reorder on iPhone
         proxy.dragInteractionEnabled = true
+        proxy.isScrollEnabled = false
     }
     
     private func attachmentsChanged(attachments: [CompositionAttachment]) {

Tusker/Screens/Compose/ComposeTextView.swift

@@ -101,9 +101,10 @@ struct WrappedTextView: UIViewRepresentable {
         return Coordinator(text: $text, didChange: textDidChange)
     }
     
-    class Coordinator: NSObject, UITextViewDelegate {
+    class Coordinator: NSObject, UITextViewDelegate, ComposeTextViewCaretScrolling {
         var text: Binding<String>
         var didChange: ((UITextView) -> Void)?
+        var caretScrollPositionAnimator: UIViewPropertyAnimator?
         
         init(text: Binding<String>, didChange: ((UITextView) -> Void)?) {
             self.text = text
@@ -113,6 +114,8 @@ struct WrappedTextView: UIViewRepresentable {
         func textViewDidChange(_ textView: UITextView) {
             text.wrappedValue = textView.text
             didChange?(textView)
+            
+            ensureCursorVisible(textView: textView)
         }
     }
 }

Tusker/Screens/Compose/ComposeTextViewCaretScrolling.swift

@@ -0,0 +1,60 @@
+//
+//  ComposeTextViewCaretScrolling.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 11/11/20.
+//  Copyright © 2020 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+
+protocol ComposeTextViewCaretScrolling: class {
+    var caretScrollPositionAnimator: UIViewPropertyAnimator? { get set }
+}
+
+extension ComposeTextViewCaretScrolling {
+    func ensureCursorVisible(textView: UITextView) {
+        guard textView.isFirstResponder,
+              let range = textView.selectedTextRange,
+              let scrollView = findParentScrollView(of: textView) else {
+            return
+        }
+        
+        // We use a UIViewProperty animator to change the scroll view position so that we can store the currently
+        // running one on the Coordinator. This allows us to cancel the running one, preventing multiple animations
+        // from attempting to change the scroll view offset simultaneously, causing it to jitter around. This can
+        // happen if the user is pressing return and quickly creating many new lines.
+        
+        if let existing = caretScrollPositionAnimator {
+            existing.stopAnimation(true)
+        }
+        
+        let cursorRect = textView.caretRect(for: range.start)
+        var rectToMakeVisible = textView.convert(cursorRect, to: scrollView)
+        
+        // expand the rect to be three times the cursor height centered on the cursor so that there's
+        // some space between the bottom of the line of text being edited and the top of the keyboard
+        rectToMakeVisible.origin.y -= cursorRect.height
+        rectToMakeVisible.size.height *= 3
+        
+        let animator = UIViewPropertyAnimator(duration: 0.1, curve: .linear) {
+            scrollView.scrollRectToVisible(rectToMakeVisible, animated: false)
+        }
+        self.caretScrollPositionAnimator = animator
+        animator.startAnimation()
+    }
+    
+    private func findParentScrollView(of view: UIView) -> UIScrollView? {
+        var current: UIView = view
+        while let superview = current.superview {
+            if let scrollView = superview as? UIScrollView,
+               scrollView.isScrollEnabled {
+                return scrollView
+            } else {
+                current = superview
+            }
+        }
+        
+        return nil
+    }
+}

Tusker/Screens/Compose/MainComposeTextView.swift

@@ -171,12 +171,12 @@ struct MainComposeWrappedTextView: UIViewRepresentable {
         return Coordinator(text: $text, uiState: uiState, didChange: textDidChange)
     }
     
-    class Coordinator: NSObject, UITextViewDelegate, ComposeAutocompleteHandler {
+    class Coordinator: NSObject, UITextViewDelegate, ComposeAutocompleteHandler, ComposeTextViewCaretScrolling {
         weak var textView: UITextView?
         var text: Binding<String>
         var didChange: (UITextView) -> Void
         var uiState: ComposeUIState
-        private var caretScrollPositionAnimator: UIViewPropertyAnimator?
+        var caretScrollPositionAnimator: UIViewPropertyAnimator?
         
         init(text: Binding<String>, uiState: ComposeUIState, didChange: @escaping (UITextView) -> Void) {
             self.text = text
@@ -188,54 +188,7 @@ struct MainComposeWrappedTextView: UIViewRepresentable {
             text.wrappedValue = textView.text
             didChange(textView)
             
-            ensureCursorVisible()
+            ensureCursorVisible(textView: textView)
-        }
-        
-        private func ensureCursorVisible() {
-            guard let textView = textView,
-                  textView.isFirstResponder,
-                  let range = textView.selectedTextRange,
-                  let scrollView = findParentScrollView() else {
-                return
-            }
-            
-            // We use a UIViewProperty animator to change the scroll view position so that we can store the currently
-            // running one on the Coordinator. This allows us to cancel the running one, preventing multiple animations
-            // from attempting to change the scroll view offset simultaneously, causing it to jitter around. This can
-            // happen if the user is pressing return and quickly creating many new lines.
-            
-            if let existing = caretScrollPositionAnimator {
-                existing.stopAnimation(true)
-            }
-            
-            let cursorRect = textView.caretRect(for: range.start)
-            var rectToMakeVisible = textView.convert(cursorRect, to: scrollView)
-            
-            // expand the rect to be three times the cursor height centered on the cursor so that there's
-            // some space between the bottom of the line of text being edited and the top of the keyboard
-            rectToMakeVisible.origin.y -= cursorRect.height
-            rectToMakeVisible.size.height *= 3
-            
-            let animator = UIViewPropertyAnimator(duration: 0.1, curve: .linear) {
-                scrollView.scrollRectToVisible(rectToMakeVisible, animated: false)
-            }
-            self.caretScrollPositionAnimator = animator
-            animator.startAnimation()
-        }
-        
-        private func findParentScrollView() -> UIScrollView? {
-            guard let textView = textView else { return nil }
-            
-            var current: UIView = textView
-            while let superview = current.superview {
-                if let scrollView = superview as? UIScrollView {
-                    return scrollView
-                } else {
-                    current = superview
-                }
-            }
-            
-            return nil
         }
         
         @objc func formatButtonPressed(_ sender: UIBarButtonItem) {