TextField and last input character should visible on the screen when the cursor is not shown (flutter#74722)

Author: xu-baolin

packages/flutter/lib/src/rendering/editable.dart

@@ -383,6 +383,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
   TextSelectionDelegate textSelectionDelegate;
 
   Rect? _lastCaretRect;
+  late Rect _currentCaretRect;
 
   /// Track whether position of the start of the selected text is within the viewport.
   ///
@@ -2124,7 +2125,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     return Offset(pixelPerfectOffsetX, pixelPerfectOffsetY);
   }
 
-  void _paintCaret(Canvas canvas, Offset effectiveOffset, TextPosition textPosition) {
+  void _paintCaretIfNeeded(Canvas canvas, Offset effectiveOffset, TextPosition textPosition) {
     assert(_textLayoutLastMaxWidth == constraints.maxWidth &&
            _textLayoutLastMinWidth == constraints.minWidth,
       'Last width ($_textLayoutLastMinWidth, $_textLayoutLastMaxWidth) not the same as max width constraint (${constraints.minWidth}, ${constraints.maxWidth}).');
@@ -2171,18 +2172,24 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     }
 
     caretRect = caretRect.shift(_getPixelPerfectCursorOffset(caretRect));
+    _currentCaretRect = caretRect;
+
+    if (!_showCursor.value)
+      return;
 
     if (cursorRadius == null) {
       canvas.drawRect(caretRect, paint);
     } else {
       final RRect caretRRect = RRect.fromRectAndRadius(caretRect, cursorRadius!);
       canvas.drawRRect(caretRRect, paint);
     }
+  }
 
-    if (caretRect != _lastCaretRect) {
-      _lastCaretRect = caretRect;
+  void _updateCaretRect() {
+    if (_currentCaretRect != _lastCaretRect) {
+      _lastCaretRect = _currentCaretRect;
       if (onCaretChanged != null)
-        onCaretChanged!(caretRect);
+        onCaretChanged!(_currentCaretRect);
     }
   }
 
@@ -2333,11 +2340,11 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     final Offset effectiveOffset = offset + _paintOffset;
 
     bool showSelection = false;
-    bool showCaret = false;
+    bool canShowCaret = false;
 
     if (selection != null && !_floatingCursorOn) {
-      if (selection!.isCollapsed && _showCursor.value && cursorColor != null)
-        showCaret = true;
+      if (selection!.isCollapsed && cursorColor != null)
+        canShowCaret = true;
       else if (!selection!.isCollapsed && _selectionColor != null)
         showSelection = true;
       _updateSelectionExtentsVisibility(effectiveOffset);
@@ -2356,17 +2363,20 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     if (paintCursorAboveText)
       _textPainter.paint(context.canvas, effectiveOffset);
 
-    if (showCaret) {
+    if (canShowCaret) {
       assert(selection != null);
-      _paintCaret(context.canvas, effectiveOffset, selection!.extent);
+      _paintCaretIfNeeded(context.canvas, effectiveOffset, selection!.extent);
+      _updateCaretRect();
     }
 
     if (!paintCursorAboveText)
       _textPainter.paint(context.canvas, effectiveOffset);
 
     if (_floatingCursorOn) {
-      if (_resetFloatingCursorAnimationValue == null)
-        _paintCaret(context.canvas, effectiveOffset, _floatingCursorTextPosition);
+      if (_resetFloatingCursorAnimationValue == null) {
+        _paintCaretIfNeeded(context.canvas, effectiveOffset, _floatingCursorTextPosition);
+        _updateCaretRect();
+      }
       _paintFloatingCaret(context.canvas, _floatingCursorOffset);
     }
   }

packages/flutter/test/material/text_field_test.dart

@@ -8574,6 +8574,51 @@ void main() {
     expect(scrollController.offset, 48.0);
   });
 
+  // Regression test for https://github.com/flutter/flutter/issues/74566
+  testWidgets('TextField and last input character are visible on the screen when the cursor is not shown', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    final ScrollController textFieldScrollController = ScrollController();
+
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(),
+      home: Scaffold(
+        body: Center(
+          child: ListView(
+            controller: scrollController,
+            children: <Widget>[
+              Container(height: 579), // Push field almost off screen.
+              TextField(
+                scrollController: textFieldScrollController,
+                showCursor: false,
+              ),
+              Container(height: 1000),
+            ],
+          ),
+        ),
+      ),
+    ));
+
+    // Tap the TextField to bring it into view.
+    expect(scrollController.offset, 0.0);
+    await tester.tapAt(tester.getTopLeft(find.byType(TextField)));
+    await tester.pumpAndSettle();
+
+    // The ListView has scrolled to keep the TextField visible.
+    expect(scrollController.offset, 48.0);
+    expect(textFieldScrollController.offset, 0.0);
+
+    // After entering some long text, the last input character remains on the screen.
+    final String testValue = 'I love Flutter!' * 10;
+    tester.testTextInput.updateEditingValue(TextEditingValue(
+      text: testValue,
+      selection: TextSelection.collapsed(offset: testValue.length),
+    ));
+    await tester.pump();
+    await tester.pumpAndSettle(); // Text scroll animation.
+
+    expect(textFieldScrollController.offset, 1602.0);
+  });
+
   group('height', () {
     testWidgets('By default, TextField is at least kMinInteractiveDimension high', (WidgetTester tester) async {
       await tester.pumpWidget(MaterialApp(