Flutter Custom Title Dropdown (Material Page Filter)

问题

Following the concept of the app bar "page filter" I'd like to put a DropdownButton as the title of the AppBar. I tried, but it doesn't look good.

https://material.io/guidelines/layout/structure.html#structure-app-bar

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  String _value = 'one';

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

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new DropdownButton<String>(
          value: _value,
          items: <DropdownMenuItem<String>>[
            new DropdownMenuItem(
              child: new Text('one'),
              value: 'one',
            ),
            new DropdownMenuItem(
              child: new Text('two'),
              value: 'two'
            ),
          ], 
          onChanged: (String value) {
            setState(() => _value = value);
          },)
      ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              'hello world',
            ),
          ],
        ),
      ),
    );
  }
}

However it looks like:

which doesn't follow the material pattern found at the link stated above due to the weird looking underline... bonus: the text and button should be white.

回答1:

Do something like this:

appBar: AppBar(
    title: Row(
      mainAxisSize: MainAxisSize.min,
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        DropdownButton(
          value: _selectedItem,
          items: _dropdownMenuItems,
          underline: SizedBox(height: 0,),
          //underline: SizedBox(),
          onChanged: onChangeDropdownItem,
        ),
       ],
      ),
    ),

Then change your dropdown menu's style here:

/// Initialize dropdown menu
List<DropdownMenuItem<String>> buildDropdownMenuItems(List menu) {
List<DropdownMenuItem<String>> items = List();
for (String li in menu) {
  items.add(
    DropdownMenuItem(
      value: li,
      child: SizedBox(
        width: 100, 
        child: Text(li, style:  TextStyle(color: labelColor, fontWeight: 
               FontWeight.bold), 
               textAlign: TextAlign.center, overflow: TextOverflow.ellipsis,),),
    ),
  );
}
return items;

}

回答2:

I did find some things that helped my situation... The widgets DropdownButtonHideUnderline and Theme will help control how the dropdown looks in the title of the AppBar

new AppBar(
  title: new Theme(
      child: new DropdownButtonHideUnderline(
      child: new DropdownButton<String>(
        value: _value,
        items: <DropdownMenuItem<String>>[
          new DropdownMenuItem(
            child: new Text('My Page'),
            value: 'one',
          ),
        ], 
        onChanged: (String value) {
          setState(() => _value = value);
        },
      ),
    ), 
    data: new ThemeData.dark(),
  ),
),

However, now the popup's background color is black to match the dark theme... not sure if there's a way to have the theme not affect the actual popup.

I personally can live with the black background color of the popup... unless someone can also solve that.

回答3:

Please just change your code to the one I have mentioned below and this one might work for your app., sorry for the bad editing of the picture. I have included the full code for your reference,.

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    home: new MyHomePage(),
  ));
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  String _value = 'one';

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

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
          title:
          new Row(
         mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          new DropdownButton<String>(
            value: _value,
            items: <DropdownMenuItem<String>>[
              new DropdownMenuItem(
                child: new Text('one'),
                value: 'one',
              ),
              new DropdownMenuItem(child: new Text('two'), value: 'two'),
            ],
            onChanged: (String value) {
              setState(() => _value = value);
            },
          ),

        ],
      )
 ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              'hello world',
            ),
          ],
        ),
      ),
    );
  }
}

See the demo here: https://codepen.io/andrerpena/pen/LYpZRqG

回答4:

To have a white menu, change data: new Theme.dark() to Theme.of(context).copyWith(brightness: Brightness.dark))

But then another problems pop : The menu is white ; but the menu options are written in white too, making them unreadable.

After a deep inspection, it seems like it's currently not possible to have options using a different font color in the iddle state and when the dropdown is focused. Consider creating an issue on their github

来源：https://stackoverflow.com/questions/49156899/flutter-custom-title-dropdown-material-page-filter