Fix: fix the delay of showOnScreen animation when keyboard comes up. (flutter#99546)

Author: luckysmg

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

@@ -1965,7 +1965,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     // to make sure the user can see the changes they just made. Programmatical
     // changes to `textEditingValue` do not trigger the behavior even if the
     // text field is focused.
-    _scheduleShowCaretOnScreen();
+    _scheduleShowCaretOnScreen(withAnimation: true);
     if (_hasInputConnection) {
       // To keep the cursor from blinking while typing, we want to restart the
       // cursor timer every time a new character is typed.
@@ -2498,7 +2498,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
   bool _showCaretOnScreenScheduled = false;
 
-  void _scheduleShowCaretOnScreen() {
+  void _scheduleShowCaretOnScreen({required bool withAnimation}) {
     if (_showCaretOnScreenScheduled) {
       return;
     }
@@ -2538,17 +2538,23 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
       final RevealedOffset targetOffset = _getOffsetToRevealCaret(_currentCaretRect!);
 
-      _scrollController.animateTo(
-        targetOffset.offset,
-        duration: _caretAnimationDuration,
-        curve: _caretAnimationCurve,
-      );
-
-      renderEditable.showOnScreen(
-        rect: caretPadding.inflateRect(targetOffset.rect),
-        duration: _caretAnimationDuration,
-        curve: _caretAnimationCurve,
-      );
+      if (withAnimation) {
+        _scrollController.animateTo(
+          targetOffset.offset,
+          duration: _caretAnimationDuration,
+          curve: _caretAnimationCurve,
+        );
+        renderEditable.showOnScreen(
+          rect: caretPadding.inflateRect(targetOffset.rect),
+          duration: _caretAnimationDuration,
+          curve: _caretAnimationCurve,
+        );
+      } else {
+        _scrollController.jumpTo(targetOffset.offset);
+        renderEditable.showOnScreen(
+          rect: caretPadding.inflateRect(targetOffset.rect),
+        );
+      }
     });
   }
 
@@ -2561,7 +2567,9 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
         _selectionOverlay?.updateForScroll();
       });
       if (_lastBottomViewInset < WidgetsBinding.instance.window.viewInsets.bottom) {
-        _scheduleShowCaretOnScreen();
+        // Because the metrics change signal from engine will come here every frame
+        // (on both iOS and Android). So we don't need to show caret with animation.
+        _scheduleShowCaretOnScreen(withAnimation: false);
       }
     }
     _lastBottomViewInset = WidgetsBinding.instance.window.viewInsets.bottom;
@@ -2745,7 +2753,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       WidgetsBinding.instance.addObserver(this);
       _lastBottomViewInset = WidgetsBinding.instance.window.viewInsets.bottom;
       if (!widget.readOnly) {
-        _scheduleShowCaretOnScreen();
+        _scheduleShowCaretOnScreen(withAnimation: true);
       }
       if (!_value.selection.isValid) {
         // Place cursor at the end if the selection is invalid when we receive focus.
@@ -2900,7 +2908,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       ? _value.selection != value.selection
       : _value != value;
     if (shouldShowCaret) {
-      _scheduleShowCaretOnScreen();
+      _scheduleShowCaretOnScreen(withAnimation: true);
     }
     _formatAndSetValue(value, cause, userInteraction: true);
   }

packages/flutter/test/widgets/editable_text_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui' as ui;
+
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -39,6 +41,26 @@ class _MatchesMethodCall extends Matcher {
   }
 }
 
+// Used to set window.viewInsets since the real ui.WindowPadding has only a
+// private constructor.
+class _TestWindowPadding implements ui.WindowPadding {
+  const _TestWindowPadding({
+    required this.bottom,
+  });
+
+  @override
+  final double bottom;
+
+  @override
+  double get top => 0.0;
+
+  @override
+  double get left => 0.0;
+
+  @override
+  double get right => 0.0;
+}
+
 late TextEditingController controller;
 final FocusNode focusNode = FocusNode(debugLabel: 'EditableText Node');
 final FocusScopeNode focusScopeNode = FocusScopeNode(debugLabel: 'EditableText Scope Node');
@@ -107,6 +129,51 @@ void main() {
     expect(tester.testTextInput.setClientArgs!['inputAction'], equals(serializedActionName));
   }
 
+  // Related issue: https://github.com/flutter/flutter/issues/98115
+  testWidgets('ScheduleShowCaretOnScreen with no animation when the window changes metrics', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    final Widget widget = MaterialApp(
+      home: Scaffold(
+        body: SingleChildScrollView(
+          controller: scrollController,
+          child: Column(
+            children: <Widget>[
+              Column(
+                children: List<Widget>.generate(
+                  5,
+                  (_) {
+                    return Container(
+                      height: 1200.0,
+                      color: Colors.black12,
+                    );
+                  },
+                ),
+              ),
+              SizedBox(
+                height: 20,
+                child: EditableText(
+                  controller: TextEditingController(),
+                  backgroundCursorColor: Colors.grey,
+                  focusNode: focusNode,
+                  style: const TextStyle(),
+                  cursorColor: Colors.red,
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+    await tester.pumpWidget(widget);
+    await tester.showKeyboard(find.byType(EditableText));
+    TestWidgetsFlutterBinding.instance.window.viewInsetsTestValue = const _TestWindowPadding(bottom: 500);
+    await tester.pump();
+
+    // The offset of the scrollController should change immediately after window changes its metrics.
+    final double offsetAfter = scrollController.offset;
+    expect(offsetAfter, isNot(0.0));
+  });
+
   // Regression test for https://github.com/flutter/flutter/issues/34538.
   testWidgets('RTL arabic correct caret placement after trailing whitespace', (WidgetTester tester) async {
     final TextEditingController controller = TextEditingController();