flutter - 为什么选择的值没有随着flutter反射(reflect)在showModalBottomSheet中？

Question

首先，我创建了一个设计好的 Bottom Sheet ，其中有两个列表，借助于CupertinoPicker小部件来显示数字(左侧)和选项(小时，天，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1-30最后我选择的月份号应为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','2','3','4','5','6','7','8','9','10','11','12','13','14','15','16','17','18','19','20','21','22','23','24','25','26','27','28','29','30','31'];
  List<String> reminderMonthsVal =['1','2','3','4','5','6','7','8','9','10','11','12'];
  List<String> reminderWeeksVal =['1','2','3','4'];
  String selectedReminderVal='1';
  String selectedReminderDay ='hour';

Bottom Sheet 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','day','week','month']; reminderHoursVal
                              .map(
                                (item) => Center(
                                  child: Text(
                                    item,
                                    style: TextStyle(
                                      fontSize: 16,
                                      // fontWeight:FontWeight.bold,
                                    ),
                                  ),
                                ),
                              )
                              .toList()),
                    ),
                    Expanded(
                      child: CupertinoPicker(
                        
                          scrollController: new FixedExtentScrollController(
                            initialItem: 0,
                          ),
                          itemExtent: 30,
                          backgroundColor: Colors.grey[100],
                          onSelectedItemChanged: (int val) {
                              setState(() {
                                selectedReminderDay = reminderDay[val];
                                print("selectedReminderDay:$selectedReminderDay");
                              });
                          },
                          children: reminderDay
                              .map(
                                (item) => Center(
                                  child: Text(
                                    item,
                                    style: TextStyle(
                                      fontSize: 16,
                                      // fontWeight:FontWeight.bold,
                                    ),
                                  ),
                                ),
                              )
                              .toList()),
                    ),
                  ])
                  ),
                  SizedBox(height:15),
                  // selectedVal!=null?Text(selectedVal.toString()):Container()
                  Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      Text("You'll get the reminder"),
                      Text('$selectedReminderVal $selectedReminderDay before the event')
                    ],
                  ),
                 SizedBox(height:25),
                 Padding(
                   padding: const EdgeInsets.only(left: 10, right: 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
                            )),
                          ),
                       )
                     ],
                   ),
                 )
                ],
              ),
            )  
          ),
        );
      }, 
      
    );
  }

截屏:

Answer 1

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对话框，并且构建器会在父状态之外构建一个全新的小部件，以创建其自己的有状态状态，并用有状态的构建器和用户对其进行包装自己的setState可以在此上下文中更改任何内容，而不是父对象
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: ... ),

}