单击 DropdownButton 时应用程序崩溃（Flutter）

Question

所以我在我的应用程序中创建了一个 DropdownButton。问题是，每当我单击下拉菜单时，应用程序就会崩溃。我很困惑，因为当我在单击 DropdownButton 之前单击其他小部件（如 TextFormFields）时，它似乎工作正常。

错误信息： 'package:flutter/src/material/dropdown.dart': Failed assertion: line 581 pos 12: 'menuHeight == menuBottom - menuTop': is not true.

这是我的下拉按钮：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: DropDownTry(),
    );
  }
}

class DropDownTry extends StatefulWidget {
  const DropDownTry({Key? key}) : super(key: key);

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

class _DropDownTryState extends State<DropDownTry> {
  String dropdownValue = 'Male';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(
        child: Padding(
            padding: const EdgeInsets.all(20.0),
            child: DropdownButton<String>(
              value: dropdownValue,
              icon: const Icon(Icons.arrow_downward),
              iconSize: 24,
              elevation: 16,
              underline: SizedBox(),
              onChanged: (String? newValue) {
                setState(() {
                  dropdownValue = newValue!;
                });
              },
              items: <String>['Male', 'Female']
                  .map<DropdownMenuItem<String>>((String value) {
                return DropdownMenuItem<String>(
                  value: value,
                  child: Text(value),
                );
              }).toList(),
            )),
      ),
    );
  }
}

Answer 1

尝试下面的代码希望它能帮助您尝试删除SizedBox Widgetconst的关键字

为默认下拉值声明一个字符串变量

  String? dropdownValue;

您的下拉列表

List gender = [
    'Male',
    'Female',
    'Other',
  ];

您的下拉小部件

DropdownButtonHideUnderline(
              child: DropdownButton(
                hint: Text(
                  'Select Gender',
                  style: TextStyle(
                    color: Colors.black,
                    fontSize: 15,
                  ),
                  textAlign: TextAlign.center,
                ),
                value: dropdownValue,
                onChanged: (String? genderNewValue) {
                  setState(
                    () {
                      dropdownValue = genderNewValue;
                    },
                  );
                },
                items: gender.map<DropdownMenuItem<String>>(
                  (value) {
                    return DropdownMenuItem<String>(
                      value: value,
                      child: Text(
                        value,
                        style: TextStyle(
                          fontSize: 15,
                        ),
                      ),
                    );
                  },
                ).toList(),
              ),
            ),

您的结果屏幕：