flutter - 使用 TextField 会引发 “No Material widget found” 错误

Question

大家好，我是 Flutter 的新手，我正在尝试做一个菜单，您可以在其中添加和删除一些玩家。问题是我收到“未找到任何 Material 小部件”。错误。我究竟做错了什么 ？谢谢你。

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代码:

import 'package:flutter/material.dart';

class PlayerList extends StatefulWidget {


  const PlayerList({
    this.initialCount = 5,
  });

  // also allow for a dynamic number of starting players
  final int initialCount;

  @override
  _PlayerListState createState() => _PlayerListState();
}

class _PlayerListState extends State<PlayerList> {
  int fieldCount = 0;
  int nextIndex = 0;

  // you must keep track of the TextEditingControllers if you want the values to persist correctly
  List<TextEditingController> controllers = <TextEditingController>[];

  // create the list of TextFields, based off the list of TextControllers
  List<Widget> _buildList() {
    int i;
    // fill in keys if the list is not long enough (in case we added one)
    if (controllers.length < fieldCount) {
      for (i = controllers.length; i < fieldCount; i++) {
        controllers.add(TextEditingController());
      }
    }

    i = 0;
    // cycle through the controllers, and recreate each, one per available controller
    return controllers.map<Widget>((TextEditingController controller) {
      int displayNumber = i + 1;
      i++;

      return TextField(
          controller: controller,
          maxLength: 20,
          decoration: InputDecoration(
          labelText: "Player $displayNumber",
          counterText: "",
          prefixIcon: const Icon(Icons.person),
          suffixIcon: IconButton(
            icon: Icon(Icons.clear),
            onPressed: () {
              // when removing a TextField, you must do two things:
              // 1. decrement the number of controllers you should have (fieldCount)
              // 2. actually remove this field's controller from the list of controllers
              setState(() {
                fieldCount--;
                controllers.remove(controller);
              });
            },
          ),
          ),
      );
    }).toList(); // convert to a list
  }


  @override
  Widget build(BuildContext context) {

    // generate the list of TextFields
    final List<Widget> children = _buildList();


    // append an 'add player' button to the end of the list
    children.add(
      GestureDetector(
        onTap: () {
          // when adding a player, we only need to inc the fieldCount, because the _buildList()
          // will handle the creation of the new TextEditingController
          setState(() {
            fieldCount++;
          });
        },
        child: Container(
          color: Colors.blue,
          child: Padding(
            padding: const EdgeInsets.all(16),
            child: Text(
              'Spieler hinzufügen',
              style: TextStyle(
                color: Colors.white,
              ),
            ),
          ),
        ),
      ),

    );

    // build the ListView
    return ListView(
      padding: EdgeInsets.all(0),
      shrinkWrap: true,
      physics: NeverScrollableScrollPhysics(),
      children: children,

    );
  }


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

    // upon creation, copy the starting count to the current count
    fieldCount = widget.initialCount;
  }

  @override
  void dispose() {
    super.dispose();
  }

  @override
  void didUpdateWidget(PlayerList oldWidget) {
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
  }
}

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这是错误堆栈:

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following assertion was thrown building TextField(controller: TextEditingController#ecada(TextEditingValue(text: ┤├, selection: TextSelection(baseOffset: -1, extentOffset: -1, affinity: TextAffinity.downstream, isDirectional: false), composing: TextRange(start: -1, end: -1))), decoration: InputDecoration(labelText: "Player 1", prefixIcon: Icon(IconData(U+0E7FD)), suffixIcon: IconButton(Icon, padding: EdgeInsets.all(8.0)), counterText: ), maxLength: 20, dirty, state: _TextFieldState#edbe3):
No Material widget found.

TextField widgets require a Material widget ancestor.
In material design, most widgets are conceptually "printed" on a sheet of material. In Flutter's material library, that material is represented by the Material widget. It is the Material widget that renders ink splashes, for instance. Because of this, many material library widgets require that there be a Material widget in the tree above them.

To introduce a Material widget, you can either directly include one, or use a widget that contains Material itself, such as a Card, Dialog, Drawer, or Scaffold.

The specific widget that could not find a Material ancestor was: TextField
  controller: TextEditingController#ecada(TextEditingValue(text: ┤├, selection: TextSelection(baseOffset: -1, extentOffset: -1, affinity: TextAffinity.downstream, isDirectional: false), composing: TextRange(start: -1, end: -1)))
  decoration: InputDecoration(labelText: "Player 1", prefixIcon: Icon(IconData(U+0E7FD)), suffixIcon: IconButton(Icon, padding: EdgeInsets.all(8.0)), counterText: )
  maxLength: 20
  dirty
  state: _TextFieldState#edbe3
The ancestors of this widget were: 
  : ListView
    scrollDirection: vertical
    primary: using primary controller
    NeverScrollableScrollPhysics
    shrinkWrap: shrink-wrapping
    padding: EdgeInsets.zero
  : PlayerList
    state: _PlayerListState#89cb2
  : MaterialApp
    state: _MaterialAppState#2ca5b
  : MyApp
  ...
The relevant error-causing widget was: 
  TextField file:///C:/Flutter%20Project/flutter_app/flutter_app/lib/Pages/HomeTrinkspiel.dart:184:14
When the exception was thrown, this was the stack: 
#0      debugCheckHasMaterial.<anonymous closure> (package:flutter/src/material/debug.dart:28:7)
#1      debugCheckHasMaterial (package:flutter/src/material/debug.dart:50:4)
#2      _TextFieldState.build (package:flutter/src/material/text_field.dart:898:12)
#3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4334:27)
#4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4223:15)
...
════════════════════════════════════════════════════════════════════════════════════════════════════

Answer 1

让我们阅读错误消息:TextField widgets require a Material widget ancestor.这表明您的 TextField 小部件从 List<Widget> _buildList() 呈现缺少 Material 小部件祖先，这意味着您的父方法需要 MaterialApp和一个 Scaffold (通常)。

Perhaps this existing question/answer may help you.