import 'package:flutter/material.dart';
class CustomDropDownButton extends StatefulWidget {
  @override
  _CustomDropDownButtonState createState() => _CustomDropDownButtonState();
}

class _CustomDropDownButtonState extends State<CustomDropDownButton> {
  Color _color = Colors.red;
  final _colors = [Colors.red, Colors.yellow, Colors.blue, Colors.green];
  final _info = ["红色", "黄色", "蓝色", "绿色"];

  @override
  Widget build(BuildContext context) {
    return Wrap(
      children: <Widget>[
        Container(
          margin: EdgeInsets.symmetric(horizontal: 20),
          width: 50,
          height: 50,
          color: _color,
        ),
        DropdownButton<Color>(
            value: _color,
            elevation: 1,
            icon: Icon(
              Icons.expand_more,
              size: 20,
              color: _color,
            ),
            items: _buildItems(),
            onChanged: (v) => setState(() => _color = v)),
      ],
    );
  }

  List<DropdownMenuItem<Color>> _buildItems() => _colors
      .map((e) => DropdownMenuItem<Color>(
          value: e,
          child: Text(
            _info[_colors.indexOf(e)],
            style: TextStyle(color: e),
          )))
      .toList();
}

向上弹出

  /**
   * 向上弹出
   */
  _showPopWindow() {
    showModalBottomSheet<String>(
        context: context,
        isDismissible: true, //设置点击弹窗外边是否关闭页面
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.only(
              topLeft: Radius.circular(20), topRight: Radius.circular(20)),
        ),
        builder: (BuildContext context) {
          return Container(
            padding: EdgeInsets.symmetric(vertical: ScreenUtil().setHeight(30)),
            child: Column(
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                ListTile(
                  leading: new Icon(Icons.photo_camera),
                  title: new Text("Camera"),
                  onTap: () async {
                    Navigator.pop(context, 'camera');
                  },
                ),
                ListTile(
                  leading: new Icon(Icons.photo_library),
                  title: new Text("Gallery"),
                  onTap: () async {
                    Navigator.pop(context, 'Gallery');
                  },
                ),
              ],
            ),
          );
        }).then((value) => print('showModalBottomSheet $value'));
  }