Android studio 在“颤振”的“警报”对话框中添加下拉菜单

当我试图在我的flatter应用程序的警报对话框中添加带有日期和时间选择器的下拉菜单时，我遇到了UI呈现问题。我已经尝试解决这个问题很长一段时间了，但是没有用。这是我得到的输出：

我的代码：

    import 'dart:async';

   import 'package:flutter/material.dart';
   import 'package:firebase_database/firebase_database.dart';
   import 'package:test_prep/utils/Reminder.dart';
   import 'package:intl/intl.dart';

 class RemindersPage extends StatefulWidget {
 @override
_RemindersPageState createState() => _RemindersPageState();
 }

class _RemindersPageState extends State<RemindersPage> {
final TextEditingController _titleController = new 
TextEditingController();

List<DropdownMenuItem<Future>> dateDrop = [];
List<DropdownMenuItem<Future>> timeDrop = [];
int selected = null;


void loadDateData() {
dateDrop = [];
dateDrop.add(new DropdownMenuItem(
  child: new Text('Pick Date'),
  value: _selectedDate(context),
));
}

void loadTimeData() {
 timeDrop = [];
 timeDrop.add(new DropdownMenuItem(
  child: new Text('Pick a Time'),
  value: _selectedTime(context),
));
}

@override
Widget build(BuildContext context) {

导入'dart:async'；
进口“包装：颤振/材料.省道”；
导入“package:firebase_database/firebase_database.dart”；
导入“package:test_prep/utils/rementer.dart”；
导入“包：intl/intl.dart”；
类提醒页面扩展StatefulWidget{
@凌驾
_提醒页面状态createState（）=>_提醒页面状态（）；
}
类_提醒页面状态扩展状态{
最终文本编辑控制器\u标题控制器=新建
TextEditingController（）；
List dateDrop=[]；
列表时间差=[]；
int selected=null；
void loadDateData（）{
dateDrop=[]；
添加（新的DropdownMenuItem）(
子项：新文本（“拾取日期”），
值：_selectedDate（上下文），
));
}
void loadTimeData（）{
时间差=[]；
添加（新的下拉菜单项）(
子项：新文本（“选择时间”），
值：_selectedTime（上下文），
));
}
@凌驾
小部件构建（构建上下文）{

//loadDateData（）； //loadTimeData（）

返回脚手架(
背景颜色：Colors.black87，
正文：列（子项：[]），
//浮动动作按钮
floatingActionButton：新的floatingActionButton(
工具提示：“添加物品”，
背景颜色：Colors.greenAccent，
孩子：新的ListTile(
标题：图标(
Icons.add，
),
),
按下时：_showFormDialog），
底部导航栏：新主题(
数据：主题（上下文）
.copyWith（画布颜色：颜色。灰色，原色：
颜色（白色），
子项：新的底部导航栏(
项目：[
新海底导航气压计(
图标：新图标（图标。过滤器\u无），
标题：新文本（“提醒”），
新海底导航气压计(
图标：新图标（图标。全部显示），标题：新文本（“测验”））
],
onTap：（inti）=>debugPrint（“您点击了$i”），
),
),
);
}
//警报对话框
void_showFormDialog（）{
var alert=新建警报对话框(
标题：文本（“设置提醒”），
内容：列（子项：[
扩大(
孩子：TextField(
控制器：\标题控制器，
自动对焦：对，
装饰：输入装饰(
labelText:“提醒的名称”，
hintText：“例如，星期四考试！”，
图标：图标（Icons.title），
),
),
),
//日期
_dropDownDate（），
//时间
_停机时间（）
]),
行动：[
新扁平按钮(
按下时：（）=>debugPrint（“保存按钮”），子项：
文本（“保存”），
新扁平按钮(
onPressed:（）=>Navigator.pop（上下文），子项：
文本（“取消”）
],
);
显示对话框(
上下文：上下文，
建筑商：（）{
返回警报；
});
}
//日期和时间选择器
DateTime _date=new DateTime.now（）；
TimeOfDay _time=新的TimeOfDay.now（）；
Future\u selectedDate（构建上下文）异步{
选择的最终日期时间=等待showDatePicker(
上下文：上下文，
初始日期：_日期，
firstDate：新日期时间（2018年），
最后日期：新日期时间（2019年）；
如果（已拾取！=null）{
debugPrint（'所选日期：${u Date.toString（）}'）；
设置状态（）{
_日期=已拾取；
});
}
}
Future\u selectedTime（构建上下文）异步{
最后一天的时间=
等待showTimePicker（上下文：上下文，初始时间：_time）；
如果（已拾取！=null&&picked！=\u时间）{
debugPrint（'所选时间：${u Time.toString（）}'）；
设置状态（）{
_时间=已拾取；
});
}
}
_下载日期{
var drop_date=容器(
子级：行（mainAxisAlignment:mainAxisAlignment.start，子级：
[
下拉按钮(
值：选中，
项目：dateDrop，
提示：文本（“选择日期”），
一旦更改：（值）{
所选=值；
setState（（）{}）；
}),
]));
退货日期；
}
_停机时间（）{
var drop_time=容器(
子级：行（mainAxisAlignment:mainAxisAlignment.start，子级：
[
下拉按钮(
值：选中，
项目：时差，
提示：文本（“选择时间”），
一旦更改：（值）{
所选=值；
setState（（）{}）；
}),
]));
返回下降时间；
}
}

颤振运行时消息：

 Syncing files to device iPhone X...
flutter: ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
flutter: The following ArgumentError was thrown during paint():
flutter: Invalid argument(s): 0.0
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0      double.clamp (dart:core/runtime/libdouble.dart:144:7)
flutter: #1      _DropdownMenuPainter.paint (package:flutter/src/material/dropdown.dart:57:33)
flutter: #2      RenderCustomPaint._paintWithPainter (package:flutter/src/rendering/custom_paint.dart:520:13)
flutter: #3      RenderCustomPaint.paint (package:flutter/src/rendering/custom_paint.dart:558:7)
flutter: #4      RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #5      PaintingContext.paintChild (package:flutter/src/rendering/object.dart:171:13)
flutter: #6      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:126:15)
flutter: #7      PaintingContext.pushLayer (package:flutter/src/rendering/object.dart:367:12)
flutter: #8      PaintingContext.pushOpacity (package:flutter/src/rendering/object.dart:491:5)
flutter: #9      RenderAnimatedOpacity.paint (package:flutter/src/rendering/proxy_box.dart:904:15)
flutter: #10     RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #11     PaintingContext.paintChild (package:flutter/src/rendering/object.dart:171:13)
flutter: #12     RenderShiftedBox.paint (package:flutter/src/rendering/shifted_box.dart:70:15)
flutter: #13     RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #14     PaintingContext.paintChild (package:flutter/src/rendering/object.dart:171:13)
flutter: #15     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:126:15)
flutter: #16     RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #17     PaintingContext._repaintCompositedChild (package:flutter/src/rendering/object.dart:128:11)
flutter: #18     PaintingContext.repaintCompositedChild (package:flutter/src/rendering/object.dart:96:5)
flutter: #19     PipelineOwner.flushPaint (package:flutter/src/rendering/object.dart:852:29)
flutter: #20     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:272:19)
flutter: #21     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:654:13)
flutter: #22     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
flutter: #23     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
flutter: #24     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
flutter: #25     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
flutter: #26     _invoke (dart:ui/hooks.dart:128:13)
flutter: #27     _drawFrame (dart:ui/hooks.dart:117:3)
flutter:
flutter: The following RenderObject was being processed when the exception was fired:
flutter:   RenderCustomPaint#556fb relayoutBoundary=up2
flutter:   creator: CustomPaint ← FadeTransition ← _DropdownMenu<Object> ← CustomSingleChildLayout ← Builder
flutter:   ← MediaQuery ← Builder ← RepaintBoundary-[GlobalKey#4c3ae] ← IgnorePointer ← AnimatedBuilder ←
flutter:   RepaintBoundary ← _FocusScopeMarker ← ⋯
flutter:   parentData: <none> (can use size)
flutter:   constraints: BoxConstraints(w=148.0, 0.0<=h<=716.0)
flutter:   size: Size(148.0, 16.0)
flutter: This RenderObject had the following descendants (showing up to depth 5):
flutter:   RenderSemanticsAnnotations#151e5 relayoutBoundary=up3 NEEDS-PAINT
flutter:     RenderCustomPaint#b9211 relayoutBoundary=up4 NEEDS-PAINT
flutter:       _RenderInkFeatures#13585 relayoutBoundary=up5 NEEDS-PAINT
flutter:         RenderRepaintBoundary#ed5d6 relayoutBoundary=up6 NEEDS-PAINT
flutter:           RenderCustomPaint#f5290 relayoutBoundary=up7 NEEDS-PAINT
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
    [C2.1 748F7D32-4C53-4798-B15B-8E3BDB7D9006 2601:196:4801:b518:c076:dbf1:83d3:ada3.50444<->2607:f8b0:4002:c08::8b.443]
    Connected Path: satisfied (Path is satisfied), interface: en0
    Duration: 121.165s, DNS @0.004s took 0.008s, TCP @0.018s took 0.055s, TLS took 0.137s
    bytes in/out: 3879/764, packets in/out: 10/8, rtt: 0.056s, retransmitted packets: 0, out-of-order packets: 0
    [C3.1 67E05789-ED99-4A78-A900-D136E04B908C 2601:196:4801:b518:c076:dbf1:83d3:ada3.50445<->2607:f8b0:4002:c08::8b.443]
    Connected Path: satisfied (Path is satisfied), interface: en0
    Duration: 120.368s, DNS @0.002s took 0.004s, TCP @0.008s took 0.056s, TLS took 0.137s
    bytes in/out: 3591/1188, packets in/out: 9/9, rtt: 0.058s, retransmitted packets: 0, out-of-order packets: 0
    [C1.1 89EEE9E8-79C7-4861-9FD9-148DA484E6BE 2601:196:4801:b518:c076:dbf1:83d3:ada3.50428<->2607:f8b0:4002:813::200a.443]
    Connected Path: satisfied (Path is satisfied), interface: en0
    Duration: 240.659s, DNS @0.002s took 0.031s, TCP @0.036s took 0.058s, TLS took 0.563s
    bytes in/out: 3394/1027, packets in/out: 10/9, rtt: 0.057s, retransmitted packets: 0, out-of-order packets: 0

正在将文件同步到设备iPhone X。。。
颤振：══╡ 呈现库捕获到异常╞═════════════════════════════════════════════════════════
颤振：在绘制过程中引发了以下ArgumentError（）：
颤振：无效参数：0.0
颤振：
颤振：抛出异常时，这是堆栈：
颤振：#0 double.clamp（dart:core/runtime/libdouble.dart:144:7）
颤振：#1#下拉菜单uppaint.paint（包装：颤振/src/材料/下拉。省道：57:33）
颤振：#2 RenderConstompaint._paintWithPainter（包装：颤振/src/rendering/custom_paint.省道：520:13）
flatter:#3 rendercastompaint.paint（包：flatter/src/rendering/custom_-paint.dart:558:7）
flatter:#4 RenderObject._paintWithContext（包：flatter/src/rendering/object.dart:2085:7）
flatter:#5 PaintingContext.paintChild（包：flatter/src/rendering/object.dart:171:13）
颤振：#6#RenderProxy box&RenderBox&RenderObjectWithChildMixin&RenderProxy box Mixin.paint（包：颤振/src/rendering/proxy#box.省道：126:15）
flatter:#7 PaintingContext.pushLayer（包：flatter/src/rendering/object.dart:367:12）
flatter:#8 PaintingContext.pushOpacity（包：flatter/src/rendering/object.dart:491:5）
颤振：9 RenderAnimatedOpacity.paint（包：颤振/src/rendering/proxy_-box.dart:904:15）
flatter:#10 RenderObject._paintWithContext（包：flatter/src/rendering/object.dart:2085:7）
弗鲁特
 Syncing files to device iPhone X...
flutter: ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
flutter: The following ArgumentError was thrown during paint():
flutter: Invalid argument(s): 0.0
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0      double.clamp (dart:core/runtime/libdouble.dart:144:7)
flutter: #1      _DropdownMenuPainter.paint (package:flutter/src/material/dropdown.dart:57:33)
flutter: #2      RenderCustomPaint._paintWithPainter (package:flutter/src/rendering/custom_paint.dart:520:13)
flutter: #3      RenderCustomPaint.paint (package:flutter/src/rendering/custom_paint.dart:558:7)
flutter: #4      RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #5      PaintingContext.paintChild (package:flutter/src/rendering/object.dart:171:13)
flutter: #6      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:126:15)
flutter: #7      PaintingContext.pushLayer (package:flutter/src/rendering/object.dart:367:12)
flutter: #8      PaintingContext.pushOpacity (package:flutter/src/rendering/object.dart:491:5)
flutter: #9      RenderAnimatedOpacity.paint (package:flutter/src/rendering/proxy_box.dart:904:15)
flutter: #10     RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #11     PaintingContext.paintChild (package:flutter/src/rendering/object.dart:171:13)
flutter: #12     RenderShiftedBox.paint (package:flutter/src/rendering/shifted_box.dart:70:15)
flutter: #13     RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #14     PaintingContext.paintChild (package:flutter/src/rendering/object.dart:171:13)
flutter: #15     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:126:15)
flutter: #16     RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2085:7)
flutter: #17     PaintingContext._repaintCompositedChild (package:flutter/src/rendering/object.dart:128:11)
flutter: #18     PaintingContext.repaintCompositedChild (package:flutter/src/rendering/object.dart:96:5)
flutter: #19     PipelineOwner.flushPaint (package:flutter/src/rendering/object.dart:852:29)
flutter: #20     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:272:19)
flutter: #21     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:654:13)
flutter: #22     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
flutter: #23     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
flutter: #24     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
flutter: #25     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
flutter: #26     _invoke (dart:ui/hooks.dart:128:13)
flutter: #27     _drawFrame (dart:ui/hooks.dart:117:3)
flutter:
flutter: The following RenderObject was being processed when the exception was fired:
flutter:   RenderCustomPaint#556fb relayoutBoundary=up2
flutter:   creator: CustomPaint ← FadeTransition ← _DropdownMenu<Object> ← CustomSingleChildLayout ← Builder
flutter:   ← MediaQuery ← Builder ← RepaintBoundary-[GlobalKey#4c3ae] ← IgnorePointer ← AnimatedBuilder ←
flutter:   RepaintBoundary ← _FocusScopeMarker ← ⋯
flutter:   parentData: <none> (can use size)
flutter:   constraints: BoxConstraints(w=148.0, 0.0<=h<=716.0)
flutter:   size: Size(148.0, 16.0)
flutter: This RenderObject had the following descendants (showing up to depth 5):
flutter:   RenderSemanticsAnnotations#151e5 relayoutBoundary=up3 NEEDS-PAINT
flutter:     RenderCustomPaint#b9211 relayoutBoundary=up4 NEEDS-PAINT
flutter:       _RenderInkFeatures#13585 relayoutBoundary=up5 NEEDS-PAINT
flutter:         RenderRepaintBoundary#ed5d6 relayoutBoundary=up6 NEEDS-PAINT
flutter:           RenderCustomPaint#f5290 relayoutBoundary=up7 NEEDS-PAINT
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
flutter: Another exception was thrown: Invalid argument(s): 0.0
    [C2.1 748F7D32-4C53-4798-B15B-8E3BDB7D9006 2601:196:4801:b518:c076:dbf1:83d3:ada3.50444<->2607:f8b0:4002:c08::8b.443]
    Connected Path: satisfied (Path is satisfied), interface: en0
    Duration: 121.165s, DNS @0.004s took 0.008s, TCP @0.018s took 0.055s, TLS took 0.137s
    bytes in/out: 3879/764, packets in/out: 10/8, rtt: 0.056s, retransmitted packets: 0, out-of-order packets: 0
    [C3.1 67E05789-ED99-4A78-A900-D136E04B908C 2601:196:4801:b518:c076:dbf1:83d3:ada3.50445<->2607:f8b0:4002:c08::8b.443]
    Connected Path: satisfied (Path is satisfied), interface: en0
    Duration: 120.368s, DNS @0.002s took 0.004s, TCP @0.008s took 0.056s, TLS took 0.137s
    bytes in/out: 3591/1188, packets in/out: 9/9, rtt: 0.058s, retransmitted packets: 0, out-of-order packets: 0
    [C1.1 89EEE9E8-79C7-4861-9FD9-148DA484E6BE 2601:196:4801:b518:c076:dbf1:83d3:ada3.50428<->2607:f8b0:4002:813::200a.443]
    Connected Path: satisfied (Path is satisfied), interface: en0
    Duration: 240.659s, DNS @0.002s took 0.031s, TCP @0.036s took 0.058s, TLS took 0.563s
    bytes in/out: 3394/1027, packets in/out: 10/9, rtt: 0.057s, retransmitted packets: 0, out-of-order packets: 0

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new RemindersPage(),
    );
  }
}

class RemindersPage extends StatefulWidget {
  @override
  _RemindersPageState createState() => _RemindersPageState();
}

class _RemindersPageState extends State<RemindersPage> {
  final TextEditingController _titleController = new TextEditingController();

  DateTime _date = new DateTime.now();

  onDateChanged(DateTime date) {
    _date = date;
    //setState(() {}); //optional
  }

  // Alert Dialog
  void _showFormDialog() {
    var alert = new AlertDialog(
      title: Text("Set Reminder"),
      content: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          TextField(
            controller: _titleController,
            autofocus: true,
            decoration: InputDecoration(
              labelText: 'Name of Reminder',
              hintText: "eg. Test on Thursday!",
              icon: Icon(Icons.title),
            ),
          ),
          // Date
          SelectDateButton(
            date: _date,
            dateCallback: onDateChanged,
          ),
        ],
      ),
      actions: <Widget>[
        new FlatButton(
            onPressed: () => debugPrint("Save button"), child: Text('Save')),
        new FlatButton(
            onPressed: () => Navigator.pop(context), child: Text('Cancel'))
      ],
    );
    showDialog(
        context: context,
        builder: (_) {
          return alert;
        });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black87,
      body: Column(children: <Widget>[]),

      // Floating Action button
      floatingActionButton: new FloatingActionButton(
        tooltip: "Add Item",
        backgroundColor: Colors.greenAccent,
        child: new ListTile(title: Icon(Icons.add)),
        onPressed: _showFormDialog,
      ),
    );
  }
}

class SelectDateButton extends StatefulWidget {
  final DateTime date;

  final ValueChanged<DateTime> dateCallback;

  SelectDateButton({Key key, this.date, this.dateCallback}) : super(key: key);

  @override
  SelectDateButtonState createState() {
    return new SelectDateButtonState();
  }
}

class SelectDateButtonState extends State<SelectDateButton> {
  DateTime _date;

  @override
  void initState() {
    super.initState();
    _date = widget.date;
  }

  void selectDate(BuildContext context) async {
    final DateTime picked = await showDatePicker(
      context: context,
      initialDate: _date,
      firstDate: new DateTime(2018),
      lastDate: new DateTime(2019),
    );
    if (picked != null) {
      widget.dateCallback(picked);
      _date = picked;
      setState(() {});
    }
  }

  @override
  Widget build(BuildContext context) {
    return FlatButton(
      onPressed: () => selectDate(context),
      child: Row(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          Text("${_date.toString().substring(0, 10)}"),
          Icon(Icons.arrow_drop_down),
        ],
      ),
    );
  }
}

Future _showDialog(context) async {
 return await showDialog<void>(
   context: context,
   builder: (BuildContext context) {
     return AlertDialog(
       content: StatefulBuilder(
         builder: (BuildContext context, StateSetter setState) {
           return Column(
             mainAxisSize: MainAxisSize.min,
             children: <Widget>[
               //your code dropdown button here
             ]),
           );
         },
       ),
     );
   },
 );
}