如何在 Flutter 中添加装饰 DropdownButton

Question

我有一个下拉按钮，如下所示。

  child: DropdownButton<String>(
                              value: dropDownValue,
                              icon: Icon(Icons.keyboard_arrow_down),
                              iconSize: 15,
                              elevation: 16,
                              style: TextStyle(color: Colors.grey),
                              underline: Container(
                                decoration: ShapeDecoration(
                                  shape: RoundedRectangleBorder(
                                    side: BorderSide(width: 1.0, style: BorderStyle.solid),
                                    borderRadius: BorderRadius.all(Radius.circular(5.0)),
                                  ),
                                ),
                            ),
                              onChanged: (String newValue) {
                                setState(() {
                                  dropDownValue = newValue;
                                });
                              },
                              items: [dropDownValue,...snapshot.data.data]
                                  .map<DropdownMenuItem<String>>((String value) {
                                return DropdownMenuItem<String>(
                                  value: value,
                                  child: Text(value.name),
                                );
                              }).toList(),
                            ),

我想通过在容器中使用装饰来像图像中一样塑造它，但我无法按照我想要的方式塑造它

但现在这是我的形象。如何向下拉按钮添加边缘？有没有已知的方法？

Answer 1

您可以将您的DropdownButton小部件包装到DecoratedBox：

return DecoratedBox(
      decoration: ShapeDecoration(
        color: Colors.cyan,
        shape: RoundedRectangleBorder(
          side: BorderSide(width: 1.0, style: BorderStyle.solid, color: Colors.cyan),
          borderRadius: BorderRadius.all(Radius.circular(25.0)),
        ),
      ),
      child: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 40.0, vertical: 0.0),
        child: DropdownButton<String>(
          value: dropdownValue,
          icon: Icon(null),
          elevation: 16,
          onChanged: (String newValue) {
            setState(() {
              dropdownValue = newValue;
            });
          },
          underline: SizedBox(),
          items: <String>['City', 'Country', 'State']
              .map<DropdownMenuItem<String>>((String value) {
            return DropdownMenuItem<String>(
              value: value,
              child: Text(value),
            );
          }).toList(),
        ),
      ),
    );

输出 ：

Answer 2

您可以复制粘贴运行完整的代码下面
您可以使用DropdownButtonFormField同InputDecoration一套fillColor和hintText
代码段

DropdownButtonFormField(
              decoration: InputDecoration(
                  border: OutlineInputBorder(
                    borderRadius: const BorderRadius.all(
                      const Radius.circular(30.0),
                    ),
                  ),
                  filled: true,
                  hintStyle: TextStyle(color: Colors.grey[800]),
                  hintText: "Name",
                  fillColor: Colors.blue[200]),
              value: dropDownValue,

工作演示

完整代码

import 'package:flutter/material.dart';

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: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  String dropDownValue;
  List<String> cityList = [
    'Ajman',
    'Al Ain',
    'Dubai',
    'Fujairah',
    'Ras Al Khaimah',
    'Sharjah',
    'Umm Al Quwain'
  ];
  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  void initState() {
    //setFilters();
    super.initState();
  }

  setFilters() {
    setState(() {
      dropDownValue = cityList[2];
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            DropdownButtonFormField(
              decoration: InputDecoration(
                  border: OutlineInputBorder(
                    borderRadius: const BorderRadius.all(
                      const Radius.circular(30.0),
                    ),
                  ),
                  filled: true,
                  hintStyle: TextStyle(color: Colors.grey[800]),
                  hintText: "Name",
                  fillColor: Colors.blue[200]),
              value: dropDownValue,
              onChanged: (String Value) {
                setState(() {
                  dropDownValue = Value;
                });
              },
              items: cityList
                  .map((cityTitle) => DropdownMenuItem(
                      value: cityTitle, child: Text("$cityTitle")))
                  .toList(),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}