flutter - TextFormField输入键，在构建过程中调用setState()-错误

Question

嗨，我试图在单击Enter键时从TextFormField向ListView添加一些值。
但是在构建过程中获取错误setState()或markNeedsBuild()
我的代码如下。

    class ScanBarcode extends StatefulWidget {
    @override
   _ScanBarcodeState createState() => _ScanBarcodeState();
    }
     class _ScanBarcodeState extends State<ScanBarcode> {
   List<String> litems = [];
   final TextEditingController eCtrl = new TextEditingController();

   @override
  Widget build(BuildContext ctxt) {
  return new Scaffold(
    appBar: new AppBar(title: new Text("Dynamic Demo"),),
    body: new Column(
      children: <Widget>[
        new TextFormField(
          controller: eCtrl,
          maxLines: null,
          autovalidate: true,
          textInputAction: TextInputAction.none,

          // ignore: missing_return
          validator: (value) {
            if (value.isEmpty==false) {
              // if(eCtrl.text.trim()!='') {
              if (value.contains('\n')) {
                debugPrint(value);
                litems.add(value); // Append Text to the list
                eCtrl.clear(); // Clear the Text area
                setState(() {});
              }
            }
            // }
          },
          decoration: InputDecoration(
              border: InputBorder.none,
              hintText: 'Enter a search term'
          ),

        ),
        new Expanded(
            child: new ListView.builder
              (
                itemCount: litems.length,
                itemBuilder: (BuildContext ctxt, int Index) {
                  return new Text(litems[Index]);
                }
            )
        )
      ],
    )
  );
  }
 }

我正在错误以下。

  setState() or markNeedsBuild() called during build

如果有评论

 setState()

它工作正常，但值未添加到列表 View 中。
任何帮助将不胜感激。

Answer 1

您可以在下面复制粘贴运行完整代码
您可以使用addPostFrameCallback程式码片段

WidgetsBinding.instance.addPostFrameCallback((_) {
                  setState(() {});
                });

工作演示

完整的代码

import 'package:flutter/material.dart';

class ScanBarcode extends StatefulWidget {
  @override
  _ScanBarcodeState createState() => _ScanBarcodeState();
}

class _ScanBarcodeState extends State<ScanBarcode> {
  List<String> litems = [];
  final TextEditingController eCtrl = TextEditingController();

  @override
  Widget build(BuildContext ctxt) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Dynamic Demo"),
        ),
        body: Column(
          children: <Widget>[
            TextFormField(
              controller: eCtrl,
              maxLines: null,
              autovalidate: true,
              textInputAction: TextInputAction.none,

              // ignore: missing_return
              validator: (value) {
                if (value.isEmpty == false) {
                  // if(eCtrl.text.trim()!='') {
                  if (value.contains('\n')) {
                    debugPrint(value);
                    litems.add(value); // Append Text to the list
                    eCtrl.clear(); // Clear the Text area
                    WidgetsBinding.instance.addPostFrameCallback((_) {
                      setState(() {});
                    });
                  }
                }
                // }
              },
              decoration: InputDecoration(
                  border: InputBorder.none, hintText: 'Enter a search term'),
            ),
            Expanded(
                child: ListView.builder(
                    itemCount: litems.length,
                    itemBuilder: (BuildContext ctxt, int Index) {
                      return Text(litems[Index]);
                    }))
          ],
        ));
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: ScanBarcode(),
    );
  }
}