为什么选择的值没有随着flutter反映在showModalBottomSheet中？

如何解决为什么选择的值没有随着flutter反映在showModalBottomSheet中？

首先，我创建了一个设计好的底部工作表，其中有两个列表，借助CupertinoPicker小部件来显示数字（左侧）和选项（小时，日，周，月），

数字将取决于我选择的选项，如果选择小时，则左侧数字应为1-24，如果选择星期，数字应为1-4，选择日期，则数字应为1。 1-30，最后我选择的月份号应该是1-12。

代码：

所有列表变量：

List<String> reminderDay = ['hour','day','week','month'];
  List<String> reminderHoursVal =['1','2','3','4','5','6','7','8','9','10','11','12','13','14','15','16','17','18','19','20','21','22','23','24'];
  List<String> reminderDaysVal =['1','24','25','26','27','28','29','30','31'];
  List<String> reminderMonthsVal =['1','12'];
  List<String> reminderWeeksVal =['1','4'];
  String selectedReminderVal='1';
  String selectedReminderDay ='hour';

底页代码：

addReminder(){ 
   
    showModalBottomSheet(
      
      context: context,builder: (BuildContext context) {
        return AnimatedPadding(
          padding: MediaQuery.of(context).viewInsets,duration: const Duration(milliseconds: 100),curve: Curves.decelerate,child: Container(
            padding: const EdgeInsets.only(top:8,right: 8,left:8,bottom: 8),height: MediaQuery.of(context).size.height/2,// color: Colors.transparent,decoration: BoxDecoration(
              color: Colors.white,borderRadius: BorderRadius.only(
                topLeft: Radius.circular(30),topRight: Radius.circular(30)
              )
            ),child: Container(
              child: Column(
                // mainAxisAlignment: MainAxisAlignment.center,crossAxisAlignment: CrossAxisAlignment.center,children: [
                  SizedBox(height:10),Text("Set a reminder",style: TextStyle(
                     fontSize:18,fontWeight:FontWeight.bold,color: Colors.grey
                   ),),SizedBox(height:20),Container(
                    margin: const EdgeInsets.only(left: 10,right: 10),height: MediaQuery.of(context).size.height/4,decoration: BoxDecoration(
                         color: Colors.grey[100],borderRadius: BorderRadius.circular(10)
                      ),child: Row(
                    crossAxisAlignment: CrossAxisAlignment.start,children: <Widget>[
                    Expanded(
                      
                      child: CupertinoPicker(
                          scrollController: new FixedExtentScrollController(
                            initialItem: 0,itemExtent: 30,backgroundColor: Colors.grey[100],onSelectedItemChanged: (int val) {
                           setState(() {
                             if(selectedReminderDay=='day'){
                               selectedReminderVal = reminderDaysVal[val];
                             }else if(selectedReminderDay=='week'){
                                selectedReminderVal = reminderWeeksVal[val];
                             }else if(selectedReminderDay=='month'){
                                selectedReminderVal = reminderMonthsVal[val];
                             }else{
                               selectedReminderVal = reminderHoursVal[val];
                             }
                              
                            print("selectedReminderVal:$selectedReminderVal");
                           });

                          },children:selectedReminderDay=='day'?reminderDaysVal
                          :selectedReminderDay=='week'?reminderWeeksVal
                            :selectedReminderDay=='month'?reminderMonthsVal:reminderHoursVal// ['hour','month']; reminderHoursVal
                              .map(
                                (item) => Center(
                                  child: Text(
                                    item,style: TextStyle(
                                      fontSize: 16,// fontWeight:FontWeight.bold,)
                              .toList()),Expanded(
                      child: CupertinoPicker(
                        
                          scrollController: new FixedExtentScrollController(
                            initialItem: 0,onSelectedItemChanged: (int val) {
                              setState(() {
                                selectedReminderDay = reminderDay[val];
                                print("selectedReminderDay:$selectedReminderDay");
                              });
                          },children: reminderDay
                              .map(
                                (item) => Center(
                                  child: Text(
                                    item,])
                  ),SizedBox(height:15),// selectedVal!=null?Text(selectedVal.toString()):Container()
                  Column(
                    mainAxisAlignment: MainAxisAlignment.center,children: [
                      Text("You'll get the reminder"),Text('$selectedReminderVal $selectedReminderDay before the event')
                    ],SizedBox(height:25),Padding(
                   padding: const EdgeInsets.only(left: 10,child: Row(
                     mainAxisAlignment: MainAxisAlignment.spaceBetween,children: [
                       InkWell(
                         onTap: (){
                           Navigator.pop(context);
                         },child: Text("Cancel",style: TextStyle(
                            fontSize: 18,color: Colors.blue,fontWeight: FontWeight.bold
                          ),InkWell(
                         onTap: (){
                          
                            Navigator.pop(context);
                         },child: Container(
                            alignment: Alignment.center,decoration: BoxDecoration(
                              color: Colors.blue,borderRadius: BorderRadius.circular(8)
                            ),width: MediaQuery.of(context).size.width/5,height: MediaQuery.of(context).size.height/25,child: Text("Save",style:TextStyle(
                              color: Colors.white,fontSize: 19
                            )),)
                     ],)
                ],)  
          ),);
      },);
  }

屏幕截图：

解决方法

这是因为您要设置的状态不同于模式底部工作表中的状态。

现在，当您调用setState时，实际上是在模态底部工作表下重建有状态的小部件。

要解决此问题，只需将底部工作表包裹在有状态的构建器中即可。

StatefulBuilder(
            builder: (context,setState) {
              return AnimatedPadding(
              padding: MediaQuery.of(context).viewInsets,duration: const Duration(milliseconds: 100),curve: Curves.decelerate,child: Container(
                padding: const EdgeInsets.only(top:8,right: 8,left:8,bottom: 8),height: MediaQuery.of(context).size.height/2,// color: Colors.transparent,decoration: BoxDecoration(
                  color: Colors.white,....

,

当我们在现有状态下创建新的上下文小部件时，状态会有所不同，bottomSheets类似于具有新上下文的dialogBox，并且构建器会在父状态之外构建一个全新的小部件，以创建自己的有状态状态用状态构建器进行包装和用户自己的setState可以在此上下文中更改任何内容，而不是父项 例如：

StatefulBuilder(
 builder: (context,setStateChild) {
            return AnimatedPadding(...
                    Expanded(
                  child: CupertinoPicker(
                    
                      scrollController: new FixedExtentScrollController(
                        initialItem: 0,),itemExtent: 30,backgroundColor: Colors.grey[100],onSelectedItemChanged: (int val) {
                          setStateChild(() {
                            selectedReminderDay = reminderDay[val];
                            print("selectedReminderDay:$selectedReminderDay");
                          });
                      },);
                 child: ... ),

}