Question

当我在Flutter中使用 TextField 小部件并将属性 autoFocus 的值设置为 true

时

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: TextField(
          autofocus: true,
        ),
      ),
    );
  }
}

flutter抛出错误

I/flutter (31721): ══╡ EXCEPTION CAUGHT BY FOUNDATION LIBRARY ╞════════════════════════════════════════════════════════
I/flutter (31721): The following assertion was thrown while dispatching notifications for FocusNode:
I/flutter (31721): RenderBox was not laid out: RenderEditable#bf516 NEEDS-LAYOUT NEEDS-PAINT
I/flutter (31721): 'package:flutter/src/rendering/box.dart':
I/flutter (31721): Failed assertion: line 1687 pos 12: 'hasSize'
I/flutter (31721):
I/flutter (31721): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter (31721): more information in this error message to help you determine and fix the underlying cause.
I/flutter (31721): In either case, please report this assertion by filing a bug on GitHub:
I/flutter (31721):   https://github.com/flutter/flutter/issues/new?template=BUG.md
I/flutter (31721):
I/flutter (31721): When the exception was thrown, this was the stack:
I/flutter (31721): #2      RenderBox.size 
package:flutter/…/rendering/box.dart:1687
I/flutter (31721): #3      EditableTextState._updateSizeAndTransform 
package:flutter/…/widgets/editable_text.dart:1729
I/flutter (31721): #4      EditableTextState._openInputConnection 
package:flutter/…/widgets/editable_text.dart:1415
I/flutter (31721): #5      EditableTextState._openOrCloseInputConnectionIfNeeded 
package:flutter/…/widgets/editable_text.dart:1441
I/flutter (31721): #6      EditableTextState._handleFocusChanged 
package:flutter/…/widgets/editable_text.dart:1707
I/flutter (31721): #7      ChangeNotifier.notifyListeners 
package:flutter/…/foundation/change_notifier.dart:206
I/flutter (31721): #8      FocusNode._notify 
package:flutter/…/widgets/focus_manager.dart:808
I/flutter (31721): #9      FocusManager._applyFocusChange 
package:flutter/…/widgets/focus_manager.dart:1401
I/flutter (31721): (elided 12 frames from class _AssertionError and package dart:async)
I/flutter (31721):
I/flutter (31721): The FocusNode sending notification was:
I/flutter (31721):   FocusNode#ce6fe
I/flutter (31721): ════════════════════════════════════════════════════════════════════════════════════════════════════

为什么，如何解决这个问题。

我扑扑的版本：

[√] Flutter（频道稳定，v1.12.13 + hotfix.5，在Microsoft Windows上[版本10.0.18362.535]，语言环境en-US）[√] Android工具链-为Android设备开发（Android SDK版本29.0）。 2）[√] Android Studio（3.5版）[√] VS代码（1.41.0版）[√]已连接设备（1个可用）•未发现问题！

================================================ =======================

Answer 1

即使在官方示例https://flutter.dev/docs/cookbook/forms/focus中，也存在此问题
因为有了自动聚焦，键盘才会首先显示，但文本字段仍然不存在
解决方法是使用FocusNode和WidgetsBinding.instance.addPostFrameCallback
显示TextField并将焦点移到此TextField时

代码段

@override
  void initState(){
    super.initState();
    myFocusNode = FocusNode();
    WidgetsBinding.instance.addPostFrameCallback((_){
      FocusScope.of(context).requestFocus(myFocusNode);
    });
  }

完整代码

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  FocusNode myFocusNode;

  @override
  void initState(){
    super.initState();
    myFocusNode = FocusNode();
    WidgetsBinding.instance.addPostFrameCallback((_){
      FocusScope.of(context).requestFocus(myFocusNode);
    });
  }

  @override
  void dispose() {
    // Clean up the focus node when the Form is disposed.
    myFocusNode.dispose();

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: TextField(
          //autofocus: true,
          focusNode: myFocusNode,
        ),
      ),
    );
  }
}

Answer 2

此错误已得到修复，但目前尚未在稳定的通道（https://github.com/flutter/flutter/issues/52221）中修复。如果您的项目允许，则可以切换到dev通道（> 1.15）并仅使用自动对焦。

从命令行：

flutter channel dev
flutter upgrade

重建您的项目，它应该可以工作。

Answer 3

在2020年，即使在开发者通道中也仍然会发生此错误...

我不好，它正在工作。我的变量为null并收到错误，对不起

当我在自动对焦中使用文本字段时，Flutter引发错误

3 个答案: