文本字段返回空；绕过等待

Question

我正在制作一个计数器应用程序，并希望能够通过使用弹出输入框从用户那里获取输入来更改应用程序栏的标题。

我试图让用户在 AlertDialog 中输入一个名称（字符串），其中包含 textfield 并尝试接收通过为弹出窗口定义一个函数，在主页中输入字符串，returns 按下确认按钮时输入的字符串。我在主页的 onPressed() 中使用 await 为该函数分配一个变量，然后在 snackbar 中显示字符串变量更改。但是，只要我点击文本字段，甚至没有提交或点击确认按钮，小吃店就会出现。看起来要么是 await 不工作，要么是出于某种原因，当我点击文本字段时，Alertdialog 的 parent 函数返回 null。

import 'package:flutter/material.dart';
void main() => runApp(MaterialApp(


     home: CounterApp(),
    ));

class CounterApp extends StatefulWidget {

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

class _CounterAppState extends State<CounterApp> {


  int num = 0;
  String name = 'MyCounter-1';



 Future<String> changeName() async {

    final _controller = TextEditingController();

    showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(15)
          ),
          title: Text('Change counter name'),
          content: TextField(
            controller: _controller,
            onSubmitted: (str) {
              //Navigator.of(context).pop(str);
            },
          ),
          actions: <Widget>[
            FlatButton(
              onPressed: () {
                Navigator.of(context).pop(_controller.text.toString());
              },
              child: Text(
                'Confirm',
                style: TextStyle(
                  fontSize: 18.0,
                ),
              ),
            ),
            FlatButton(
              onPressed: () {
                Navigator.of(context).pop();
              },
              child: Text(
                'Cancel',
                style: TextStyle(
                  fontSize: 18.0,
                ),
              ),
            ),
          ],
        );
      },
    );
  }

  void snackBar(BuildContext context, String string) {
    final snackbar = SnackBar(content: Text('Counter renamed to $string'),);
    Scaffold.of(context).showSnackBar(snackbar);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(name),
        centerTitle: true,
        actions: <Widget>[
          IconButton(
            onPressed: () {
              setState(() {
                num = 0;
              });
            },
            icon: Icon(
              Icons.refresh,
              size: 35.0,
            ),
          ),
          Builder(
            builder: (context) => IconButton(
              onPressed: () async {
                setState(() async {
                  name = await changeName();
                  snackBar(context, name);
                });
              },
              icon: Icon(
                Icons.edit,
                size: 35.0,
              ),
            ),
          ),
        ],
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: <Widget>[
          Expanded(
            flex: 2,
            child: Container(
              child: Center(child: Text(
                '$num',
                style: TextStyle(
                  fontSize: 75,
                ),
              )),
            ),
          ),
          Padding(
            padding: const EdgeInsets.fromLTRB(20, 0, 20, 10),
            child: RaisedButton(
              onPressed: () {
                setState(() {
                  num += 1;
                });
              },

              shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.circular(25.0)
              ),
              color: Colors.blue,
              child: Text(
                '+',
                style: TextStyle(
                  fontSize: 100.0,
                ),
              ),
            ),
          ),
          Padding(
            padding: const EdgeInsets.fromLTRB(20, 0, 20, 20),
            child: RaisedButton(
              onPressed: () {
                setState(() {
                  num -= 1;
                });
              },
              shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(25.0)
              ),
              color: Colors.grey,
              child: Text(
                '-',
                style: TextStyle(
                  fontSize: 100.0,
                ),
              ),
            ),
          )
        ],
      ),
    );
  }
}

只要我点击编辑按钮，就会发生这种情况： Image of problem

Answer 1

只需在showDialog()之前添加await关键字，最后添加return语句，如下代码所示。

Future<String> changeName() async {
    final _controller = TextEditingController();

    await showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(15)),
          title: Text('Change counter name'),
          content: TextField(
            controller: _controller,
            onSubmitted: (str) {
              //Navigator.of(context).pop(str);
            },
          ),
          actions: <Widget>[
            FlatButton(
              onPressed: () {
                Navigator.of(context).pop(_controller.text.toString());
              },
              child: Text(
                'Confirm',
                style: TextStyle(
                  fontSize: 18.0,
                ),
              ),
            ),
            FlatButton(
              onPressed: () {
                Navigator.of(context).pop();
              },
              child: Text(
                'Cancel',
                style: TextStyle(
                  fontSize: 18.0,
                ),
              ),
            ),
          ],
        );
      },
    );

    return _controller.text;
  }

文本字段返回空；绕过等待

Textfield returning null; bypassing await

asynchronous

future

async-await

android-alertdialog

flutter