Fix edge scrolling on platforms that select word by word on long press move (#113128)

Author: Renzo-Olivares

packages/flutter/lib/src/cupertino/text_field.dart

@@ -1035,16 +1035,12 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with Restoratio
     switch (defaultTargetPlatform) {
       case TargetPlatform.iOS:
       case TargetPlatform.macOS:
-        if (cause == SelectionChangedCause.longPress
-            || cause == SelectionChangedCause.drag) {
-          _editableText.bringIntoView(selection.extent);
-        }
-        break;
       case TargetPlatform.linux:
       case TargetPlatform.windows:
       case TargetPlatform.fuchsia:
       case TargetPlatform.android:
-        if (cause == SelectionChangedCause.drag) {
+        if (cause == SelectionChangedCause.longPress
+            || cause == SelectionChangedCause.drag) {
           _editableText.bringIntoView(selection.extent);
         }
         break;

packages/flutter/lib/src/material/text_field.dart

@@ -62,45 +62,6 @@ class _TextFieldSelectionGestureDetectorBuilder extends TextSelectionGestureDete
     // Not required.
   }
 
-  @override
-  void onSingleLongTapMoveUpdate(LongPressMoveUpdateDetails details) {
-    if (delegate.selectionEnabled) {
-      final TargetPlatform targetPlatform = Theme.of(_state.context).platform;
-
-      switch (targetPlatform) {
-        case TargetPlatform.iOS:
-        case TargetPlatform.macOS:
-          renderEditable.selectPositionAt(
-            from: details.globalPosition,
-            cause: SelectionChangedCause.longPress,
-          );
-          break;
-        case TargetPlatform.android:
-        case TargetPlatform.fuchsia:
-        case TargetPlatform.linux:
-        case TargetPlatform.windows:
-          renderEditable.selectWordsInRange(
-            from: details.globalPosition - details.offsetFromOrigin,
-            to: details.globalPosition,
-            cause: SelectionChangedCause.longPress,
-          );
-          break;
-      }
-
-      switch (targetPlatform) {
-        case TargetPlatform.android:
-        case TargetPlatform.iOS:
-          editableText.showMagnifier(details.globalPosition);
-          break;
-        case TargetPlatform.fuchsia:
-        case TargetPlatform.linux:
-        case TargetPlatform.macOS:
-        case TargetPlatform.windows:
-          break;
-      }
-    }
-  }
-
   @override
   void onSingleTapUp(TapUpDetails details) {
     super.onSingleTapUp(details);
@@ -110,37 +71,19 @@ class _TextFieldSelectionGestureDetectorBuilder extends TextSelectionGestureDete
 
   @override
   void onSingleLongTapStart(LongPressStartDetails details) {
+    super.onSingleLongTapStart(details);
     if (delegate.selectionEnabled) {
-      final TargetPlatform targetPlatform = Theme.of(_state.context).platform;
-
-      switch (targetPlatform) {
+      switch (Theme.of(_state.context).platform) {
         case TargetPlatform.iOS:
         case TargetPlatform.macOS:
-          renderEditable.selectPositionAt(
-            from: details.globalPosition,
-            cause: SelectionChangedCause.longPress,
-          );
           break;
         case TargetPlatform.android:
         case TargetPlatform.fuchsia:
         case TargetPlatform.linux:
         case TargetPlatform.windows:
-          renderEditable.selectWord(cause: SelectionChangedCause.longPress);
           Feedback.forLongPress(_state.context);
           break;
       }
-
-      switch (targetPlatform) {
-        case TargetPlatform.android:
-        case TargetPlatform.iOS:
-          editableText.showMagnifier(details.globalPosition);
-          break;
-        case TargetPlatform.fuchsia:
-        case TargetPlatform.linux:
-        case TargetPlatform.macOS:
-        case TargetPlatform.windows:
-          break;
-      }
     }
   }
 }
@@ -1150,16 +1093,12 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
     switch (Theme.of(context).platform) {
       case TargetPlatform.iOS:
       case TargetPlatform.macOS:
-        if (cause == SelectionChangedCause.longPress
-            || cause == SelectionChangedCause.drag) {
-          _editableText?.bringIntoView(selection.extent);
-        }
-        break;
       case TargetPlatform.linux:
       case TargetPlatform.windows:
       case TargetPlatform.fuchsia:
       case TargetPlatform.android:
-        if (cause == SelectionChangedCause.drag) {
+        if (cause == SelectionChangedCause.longPress
+            || cause == SelectionChangedCause.drag) {
           _editableText?.bringIntoView(selection.extent);
         }
         break;

packages/flutter/lib/src/widgets/text_selection.dart

@@ -1996,10 +1996,21 @@ class TextSelectionGestureDetectorBuilder {
   @protected
   void onSingleLongTapStart(LongPressStartDetails details) {
     if (delegate.selectionEnabled) {
-      renderEditable.selectPositionAt(
-        from: details.globalPosition,
-        cause: SelectionChangedCause.longPress,
-      );
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.iOS:
+        case TargetPlatform.macOS:
+          renderEditable.selectPositionAt(
+            from: details.globalPosition,
+            cause: SelectionChangedCause.longPress,
+          );
+          break;
+        case TargetPlatform.android:
+        case TargetPlatform.fuchsia:
+        case TargetPlatform.linux:
+        case TargetPlatform.windows:
+          renderEditable.selectWord(cause: SelectionChangedCause.longPress);
+          break;
+      }
 
       switch (defaultTargetPlatform) {
         case TargetPlatform.android:
@@ -2012,6 +2023,9 @@ class TextSelectionGestureDetectorBuilder {
         case TargetPlatform.windows:
           break;
       }
+
+      _dragStartViewportOffset = renderEditable.offset.pixels;
+      _dragStartScrollOffset = _scrollPosition;
     }
   }
 
@@ -2027,11 +2041,35 @@ class TextSelectionGestureDetectorBuilder {
   @protected
   void onSingleLongTapMoveUpdate(LongPressMoveUpdateDetails details) {
     if (delegate.selectionEnabled) {
-      renderEditable.selectPositionAt(
-        from: details.globalPosition,
-        cause: SelectionChangedCause.longPress,
+      // Adjust the drag start offset for possible viewport offset changes.
+      final Offset editableOffset = renderEditable.maxLines == 1
+          ? Offset(renderEditable.offset.pixels - _dragStartViewportOffset, 0.0)
+          : Offset(0.0, renderEditable.offset.pixels - _dragStartViewportOffset);
+      final Offset scrollableOffset = Offset(
+        0.0,
+        _scrollPosition - _dragStartScrollOffset,
       );
 
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.iOS:
+        case TargetPlatform.macOS:
+          renderEditable.selectPositionAt(
+            from: details.globalPosition,
+            cause: SelectionChangedCause.longPress,
+          );
+          break;
+        case TargetPlatform.android:
+        case TargetPlatform.fuchsia:
+        case TargetPlatform.linux:
+        case TargetPlatform.windows:
+          renderEditable.selectWordsInRange(
+            from: details.globalPosition - details.offsetFromOrigin - editableOffset - scrollableOffset,
+            to: details.globalPosition,
+            cause: SelectionChangedCause.longPress,
+          );
+          break;
+      }
+
       switch (defaultTargetPlatform) {
         case TargetPlatform.android:
         case TargetPlatform.iOS:
@@ -2070,6 +2108,8 @@ class TextSelectionGestureDetectorBuilder {
     if (shouldShowSelectionToolbar) {
       editableText.showToolbar();
     }
+    _dragStartViewportOffset = 0.0;
+    _dragStartScrollOffset = 0.0;
   }
 
   /// Handler for [TextSelectionGestureDetector.onSecondaryTap].