Error on CupertinoApp

[mateusfsilva]

Hi,

I have the following layout on a CupertinoApp and I am trying to add the keyboard_avoider to scroll the TextFields.

When I add the KeyboardAvoider widget I have the following error:

Launching lib/main.dart on iPhone Xs in debug mode...
Xcode build done.                                            6,8s
flutter: ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
flutter: The following message was thrown during layout:
flutter: A RenderFlex overflowed by 97 pixels on the bottom.
flutter:
flutter: The overflowing RenderFlex has an orientation of Axis.vertical.
flutter: The edge of the RenderFlex that is overflowing has been marked in the rendering with a yellow and
flutter: black striped pattern. This is usually caused by the contents being too big for the RenderFlex.
flutter: Consider applying a flex factor (e.g. using an Expanded widget) to force the children of the
flutter: RenderFlex to fit within the available space instead of being sized to their natural size.
flutter: This is considered an error condition because it indicates that there is content that cannot be
flutter: seen. If the content is legitimately bigger than the available space, consider clipping it with a
flutter: ClipRect widget before putting it in the flex, or using a scrollable container rather than a Flex,
flutter: like a ListView.
flutter: The specific RenderFlex in question is:
flutter:   RenderFlex#550cc relayoutBoundary=up4 OVERFLOWING
flutter:   creator: Column ← Padding ← MediaQuery ← Padding ← SafeArea ← Padding ← MediaQuery ←
flutter:   PrimaryScrollController ← Stack ← DecoratedBox ← CupertinoPageScaffold ← MyWidget ← ⋯
flutter:   parentData: offset=Offset(0.0, 25.0) (can use size)
flutter:   constraints: BoxConstraints(0.0<=w<=375.0, 0.0<=h<=383.0)
flutter:   size: Size(375.0, 383.0)
flutter:   direction: vertical
flutter:   mainAxisAlignment: start
flutter:   mainAxisSize: max
flutter:   crossAxisAlignment: stretch
flutter:   verticalDirection: down
flutter: ◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
flutter: ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
flutter: The following assertion was thrown during performLayout():
flutter: RenderFlex children have non-zero flex but incoming height constraints are unbounded.
flutter: When a column is in a parent that does not provide a finite height constraint, for example if it is
flutter: in a vertical scrollable, it will try to shrink-wrap its children along the vertical axis. Setting a
flutter: flex on a child (e.g. using Expanded) indicates that the child is to expand to fill the remaining
flutter: space in the vertical direction.
flutter: These two directives are mutually exclusive. If a parent is to shrink-wrap its child, the child
flutter: cannot simultaneously expand to fit its parent.
flutter: Consider setting mainAxisSize to MainAxisSize.min and using FlexFit.loose fits for the flexible
flutter: children (using Flexible rather than Expanded). This will allow the flexible children to size
flutter: themselves to less than the infinite remaining space they would otherwise be forced to take, and
flutter: then will cause the RenderFlex to shrink-wrap the children rather than expanding to fit the maximum
flutter: constraints provided by the parent.
flutter: The affected RenderFlex is:
flutter:   RenderFlex#435aa relayoutBoundary=up14 NEEDS-LAYOUT NEEDS-PAINT
flutter: The creator information is set to:
flutter:   Column ← ConstrainedBox ← _SingleChildViewport ← IgnorePointer-[GlobalKey#ef658] ← Semantics ←
flutter:   Listener ← _GestureSemantics ←
flutter:   RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#d6466] ← Listener ← _ScrollableScope
flutter:   ← _ScrollSemantics-[GlobalKey#3d42b] ← Scrollable ← ⋯
flutter: The nearest ancestor providing an unbounded width constraint is:
flutter:   _RenderSingleChildViewport#87742 relayoutBoundary=up12 NEEDS-LAYOUT NEEDS-PAINT
flutter:   creator: _SingleChildViewport ← IgnorePointer-[GlobalKey#ef658] ← Semantics ← Listener ←
flutter:   _GestureSemantics ← RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#d6466] ←
flutter:   Listener ← _ScrollableScope ← _ScrollSemantics-[GlobalKey#3d42b] ← Scrollable ←
flutter:   SingleChildScrollView ← LayoutBuilder ← ⋯
flutter:   parentData: <none> (can use size)
flutter:   constraints: BoxConstraints(0.0<=w<=375.0, 0.0<=h<=640.0)
flutter:   size: MISSING
flutter: See also: https://flutter.dev/layout/
flutter: If this message did not help you determine the problem, consider using debugDumpRenderTree():
flutter:   https://flutter.dev/debugging/#rendering-layer
flutter:   http://docs.flutter.io/flutter/rendering/debugDumpRenderTree.html
flutter: If none of the above helps enough to fix this problem, please don't hesitate to file a bug:
flutter:   https://github.com/flutter/flutter/issues/new?template=BUG.md
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0      RenderFlex.performLayout.<anonymous closure> 
flutter: #1      RenderFlex.performLayout 
flutter: #2      RenderObject.layout 
flutter: #3      RenderConstrainedBox.performLayout 
flutter: #4      RenderObject.layout 
flutter: #5      _RenderSingleChildViewport.performLayout 
flutter: #6      RenderObject.layout 
flutter: #7      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #8      RenderObject.layout 
flutter: #9      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #10     RenderObject.layout 
flutter: #11     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #12     RenderObject.layout 
flutter: #13     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #14     RenderObject.layout 
flutter: #15     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #16     RenderObject.layout 
flutter: #17     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #18     RenderObject.layout 
flutter: #19     _RenderLayoutBuilder.performLayout 
flutter: #20     RenderObject.layout 
flutter: #21     RenderPadding.performLayout 
flutter: #22     RenderObject.layout 
flutter: #23     RenderPadding.performLayout 
flutter: #24     RenderObject.layout 
flutter: #25     RenderPadding.performLayout 
flutter: #26     RenderObject.layout 
flutter: #27     RenderPadding.performLayout 
flutter: #28     RenderObject.layout 
flutter: #29     RenderStack.performLayout 
flutter: #30     RenderObject.layout 
flutter: #31     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #32     RenderObject.layout 
flutter: #33     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #34     RenderObject.layout 
flutter: #35     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #36     RenderObject.layout 
flutter: #37     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #38     RenderObject.layout 
flutter: #39     RenderStack.performLayout 
flutter: #40     RenderObject.layout 
flutter: #41     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #42     RenderObject.layout 
flutter: #43     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #44     RenderObject.layout 
flutter: #45     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #46     RenderObject.layout 
flutter: #47     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #48     RenderObject.layout 
flutter: #49     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #50     RenderObject.layout 
flutter: #51     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #52     RenderOffstage.performLayout 
flutter: #53     RenderObject.layout 
flutter: #54     RenderStack.performLayout 
flutter: #55     RenderObject.layout 
flutter: #56     __RenderTheatre&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #57     RenderObject.layout 
flutter: #58     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #59     RenderObject.layout 
flutter: #60     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #61     RenderObject.layout 
flutter: #62     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #63     RenderObject.layout 
flutter: #64     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout 
flutter: #65     RenderObject.layout 
flutter: #66     RenderView.performLayout 
flutter: #67     RenderObject._layoutWithoutResize 
flutter: #68     PipelineOwner.flushLayout 
flutter: #69     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame 
flutter: #70     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame 
flutter: #71     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback 
flutter: #72     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback 
flutter: #73     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame 
flutter: #74     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> 
flutter: #76     _Timer._runTimers  (dart:isolate-patch/timer_impl.dart:382:19)
flutter: #77     _Timer._handleMessage  (dart:isolate-patch/timer_impl.dart:416:5)
flutter: #78     _RawReceivePortImpl._handleMessage  (dart:isolate-patch/isolate_patch.dart:171:12)
flutter: (elided one frame from package dart:async-patch)
flutter:
flutter: The following RenderObject was being processed when the exception was fired:
flutter:   RenderFlex#435aa relayoutBoundary=up14 NEEDS-LAYOUT NEEDS-PAINT
flutter:   creator: Column ← ConstrainedBox ← _SingleChildViewport ← IgnorePointer-[GlobalKey#ef658] ←
flutter:   Semantics ← Listener ← _GestureSemantics ←
flutter:   RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#d6466] ← Listener ← _ScrollableScope
flutter:   ← _ScrollSemantics-[GlobalKey#3d42b] ← Scrollable ← ⋯
flutter:   parentData: <none> (can use size)
flutter:   constraints: BoxConstraints(0.0<=w<=375.0, 640.0<=h<=Infinity)
flutter:   size: MISSING
flutter:   direction: vertical
flutter:   mainAxisAlignment: start
flutter:   mainAxisSize: max
flutter:   crossAxisAlignment: stretch
flutter:   verticalDirection: down
flutter: This RenderObject had the following descendants (showing up to depth 5):
flutter:   RenderPadding#1d1e4 relayoutBoundary=up15 NEEDS-PAINT
flutter:     RenderLimitedBox#8b8e0 relayoutBoundary=up16 NEEDS-PAINT
flutter:       RenderCustomPaint#c34fb relayoutBoundary=up17 NEEDS-PAINT
flutter:   RenderPadding#be360 relayoutBoundary=up15 NEEDS-PAINT
flutter:     RenderSemanticsAnnotations#7082f relayoutBoundary=up16 NEEDS-PAINT
flutter:       RenderIgnorePointer#d8bfb relayoutBoundary=up17 NEEDS-PAINT
flutter:         RenderDecoratedBox#f5c19 relayoutBoundary=up18 NEEDS-PAINT
flutter:           RenderPadding#86287 relayoutBoundary=up19 NEEDS-PAINT
flutter:   RenderPadding#1f407 relayoutBoundary=up15 NEEDS-PAINT
Reloaded 2 of 343 libraries in 346ms.
flutter:     RenderSemanticsAnnotations#7619a relayoutBoundary=up16 NEEDS-PAINT
flutter:       RenderIgnorePointer#fd1ba relayoutBoundary=up17 NEEDS-PAINT
flutter:         RenderDecoratedBox#02cce relayoutBoundary=up18 NEEDS-PAINT
flutter:           RenderPadding#4487a relayoutBoundary=up19 NEEDS-PAINT
flutter:   RenderPadding#0f32b relayoutBoundary=up15 NEEDS-PAINT
flutter:     RenderSemanticsAnnotations#99b22 relayoutBoundary=up16 NEEDS-PAINT
flutter:       RenderIgnorePointer#d5c23 relayoutBoundary=up17 NEEDS-PAINT
flutter:         RenderDecoratedBox#e3d8a relayoutBoundary=up18 NEEDS-PAINT
flutter:           RenderPadding#073ac relayoutBoundary=up19 NEEDS-PAINT
flutter:   RenderPadding#47695 relayoutBoundary=up15 NEEDS-PAINT
flutter:     RenderSemanticsAnnotations#ede08 relayoutBoundary=up16 NEEDS-PAINT
flutter:       RenderIgnorePointer#75445 relayoutBoundary=up17 NEEDS-PAINT
flutter:         RenderDecoratedBox#c9a60 relayoutBoundary=up18 NEEDS-PAINT
flutter:           RenderPadding#95192 relayoutBoundary=up19 NEEDS-PAINT
flutter:   RenderPadding#436d5 relayoutBoundary=up15 NEEDS-PAINT
flutter:     RenderSemanticsAnnotations#7df92 relayoutBoundary=up16 NEEDS-PAINT
flutter:       RenderIgnorePointer#7db5c relayoutBoundary=up17 NEEDS-PAINT
flutter:         RenderDecoratedBox#85e2c relayoutBoundary=up18 NEEDS-PAINT
flutter:           RenderPadding#ff8a3 relayoutBoundary=up19 NEEDS-PAINT
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
flutter: Another exception was thrown: RenderBox was not laid out: RenderFlex#435aa relayoutBoundary=up14 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: RenderConstrainedBox#e9a91 relayoutBoundary=up13 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: _RenderSingleChildViewport#87742 relayoutBoundary=up12 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: RenderIgnorePointer#7b37f relayoutBoundary=up11 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#3ac56 relayoutBoundary=up10 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: RenderPointerListener#173f1 relayoutBoundary=up9 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: RenderSemanticsGestureHandler#a7243 relayoutBoundary=up8 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: RenderPointerListener#d1336 relayoutBoundary=up7 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: _RenderScrollSemantics#f9f89 relayoutBoundary=up6 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: _RenderLayoutBuilder#55b14 relayoutBoundary=up5 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: RenderPadding#7a0f7 relayoutBoundary=up4 NEEDS-PAINT
flutter: Another exception was thrown: RenderBox was not laid out: _RenderSingleChildViewport#87742 relayoutBoundary=up12 NEEDS-PAINT
flutter: Another exception was thrown: Updated layout information required for RenderPositionedBox#b19dd NEEDS-LAYOUT NEEDS-PAINT to calculate semantics.

I am using the following code to make the app.

import 'package:flutter/cupertino.dart';
// import 'package:keyboard_avoider/keyboard_avoider.dart';

void main() => runApp(
      const MyApp(),
    );

class MyApp extends StatelessWidget {
  const MyApp() : super();

  @override
  Widget build(BuildContext context) => CupertinoApp(
        debugShowCheckedModeBanner: false,
        home: const MyWidget(),
        title: 'Test Actions Keyboard',
      );
}

class MyWidget extends StatefulWidget {
  const MyWidget() : super();

  static const Key textFieldKey01 = Key('textFieldKey01');
  static const Key textFieldKey02 = Key('textFieldKey02');
  static const Key textFieldKey03 = Key('textFieldKey03');
  static const Key textFieldKey04 = Key('textFieldKey04');
  static const Key textFieldKey05 = Key('textFieldKey05');

  @override
  State<MyWidget> createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  FocusNode focusNode01;
  TextEditingController controller01;
  FocusNode focusNode02;
  TextEditingController controller02;
  FocusNode focusNode03;
  TextEditingController controller03;
  FocusNode focusNode04;
  TextEditingController controller04;
  FocusNode focusNode05;
  TextEditingController controller05;

  @override
  void initState() {
    super.initState();

    focusNode01 = FocusNode();
    controller01 = TextEditingController();
    focusNode02 = FocusNode();
    controller02 = TextEditingController();
    focusNode03 = FocusNode();
    controller03 = TextEditingController();
    focusNode04 = FocusNode();
    controller04 = TextEditingController();
    focusNode05 = FocusNode();
    controller05 = TextEditingController();
  }

  Widget _createTextField({
    @required Key key,
    @required FocusNode focusNode,
    @required TextEditingController controller,
    @required ValueChanged<String> onSubmitted,
    TextInputAction textInputAction = TextInputAction.next,
  }) =>
      Padding(
        padding: const EdgeInsets.symmetric(
          vertical: 5.0,
          horizontal: 25.0,
        ),
        child: CupertinoTextField(
          key: key,
          controller: controller,
          focusNode: focusNode,
          clearButtonMode: OverlayVisibilityMode.editing,
          keyboardType: TextInputType.text,
          textInputAction: textInputAction,
          autofocus: false,
          autocorrect: false,
          maxLength: 50,
          onSubmitted: onSubmitted,
        ),
      );

  @override
  Widget build(BuildContext context) => CupertinoPageScaffold(
        navigationBar: CupertinoNavigationBar(
          middle: const Text(
            'Keyboard Avoider',
          ),
        ),
        backgroundColor: CupertinoColors.white,
        child: SafeArea(
          child: Padding(
            padding: const EdgeInsets.symmetric(
              vertical: 25.0,
            ),
            // child: KeyboardAvoider(
            //   autoScroll: true,
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.stretch,
              children: <Widget>[
                const Padding(
                  padding: EdgeInsets.symmetric(
                    vertical: 10.0,
                    horizontal: 25.0,
                  ),
                  child: Placeholder(
                    fallbackHeight: 250.0,
                  ),
                ),
                _createTextField(
                  key: MyWidget.textFieldKey01,
                  focusNode: focusNode01,
                  controller: controller01,
                  onSubmitted: (_) {
                    FocusScope.of(context).requestFocus(focusNode02);
                  },
                ),
                _createTextField(
                  key: MyWidget.textFieldKey02,
                  focusNode: focusNode02,
                  controller: controller02,
                  onSubmitted: (_) {
                    FocusScope.of(context).requestFocus(focusNode03);
                  },
                ),
                _createTextField(
                  key: MyWidget.textFieldKey03,
                  focusNode: focusNode03,
                  controller: controller03,
                  onSubmitted: (_) {
                    FocusScope.of(context).requestFocus(focusNode04);
                  },
                ),
                _createTextField(
                  key: MyWidget.textFieldKey04,
                  focusNode: focusNode04,
                  controller: controller04,
                  onSubmitted: (_) {
                    FocusScope.of(context).requestFocus(focusNode05);
                  },
                ),
                _createTextField(
                  key: MyWidget.textFieldKey05,
                  focusNode: focusNode05,
                  controller: controller05,
                  onSubmitted: (_) {
                    FocusScope.of(context).requestFocus(focusNode01);
                  },
                ),
                Expanded(
                  child: Container(
                    child: Container(
                      alignment: Alignment.bottomCenter,
                      child: Padding(
                        padding: const EdgeInsets.symmetric(
                          vertical: 10.0,
                          horizontal: 25.0,
                        ),
                        child: CupertinoButton(
                          color: CupertinoColors.activeBlue,
                          child: const Text(
                            'Unfocus',
                            style: TextStyle(
                              color: CupertinoColors.white,
                            ),
                          ),
                          onPressed: () {
                            FocusScope.of(context).requestFocus(FocusNode());
                          },
                        ),
                      ),
                    ),
                  ),
                ),
              ],
            ),
            // ),
          ),
        ),
      );

  @override
  void dispose() {
    focusNode01.dispose();
    controller01.dispose();
    focusNode02.dispose();
    controller02.dispose();
    focusNode03.dispose();
    controller03.dispose();
    focusNode04.dispose();
    controller04.dispose();
    focusNode05.dispose();
    controller05.dispose();

    super.dispose();
  }
}

name: test_keyboard_avoider
description: A new Flutter project.

version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  cupertino_icons: ^0.1.2

  keyboard_avoider: ^0.1.2

dev_dependencies:
  flutter_test:
    sdk: flutter

flutter:
  uses-material-design: false

Here is the flutter doctor result:

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel unknown, v1.5.8, on Mac OS X 10.14.5 18F132, locale pt-BR)

[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
[✓] iOS toolchain - develop for iOS devices (Xcode 10.2.1)
[✓] Android Studio (version 3.4)
[✓] IntelliJ IDEA Community Edition (version 2019.1.1)
[✓] VS Code (version 1.34.0)
[✓] Connected device (3 available)

• No issues found!

[martinrybak]

The issue is the Expanded widget inside your Column. That effectively gives the column infinite height. You can't have a widget of unbounded height inside a ScrollView, which is what KeyboardAvoider uses to scroll your content. Replace KeyboardAvoider with SingleChildScrollView and you'll get the same result. If you remove the Expanded widget, it will work fine.

[omarsawalhah]

But KeyboardAvoider is meant to avoid the keyboard automatically when text fields get focus, am I right. In this post, https://medium.com/flutter-nyc/avoiding-the-on-screen-keyboard-in-flutter-ae0e46ecb96c you said we can use it instead of "Scaffold", if remove the scaffold widget, you will get an error that the "TextField" needs a wrapping Material widget.

[martinrybak]

Regarding your original issue, KeyboardAvoider works by wrapping your content in a ScrollView to make it scrollable. So your content has to play nice inside a ScrollView, which means no widgets with unbounded height.

Re: your most recent comment: you can still use a Scaffold for the other features it offers (app bar, drawer, etc.). Just set resizeToAvoidBottomInset to false. Or you can give your TextField an explicit Material ancestor widget.