显示PopupMenu时键盘关闭

Question

我正在使用Flutter构建待办事项应用程序。当我按下floatingActionButton时，将显示ModalBottomSheet，当我按下“重复”按钮时，键盘将关闭，并使popupMenu浮动。如何防止键盘消失？

当我按“重复”时

这是我的代码

DateTime selectedDate = DateTime.now();
List <PopupMenuItem<String>> _pop = ['Daily', 'Weekly', 'Monthly'].map((String value){
  return PopupMenuItem <String>(
      value: value,
      child: Text(value),
   );
  }).toList();



// When press on floatingActionButton
showAddBottomSheet(BuildContext parentContext, HomeState homeState){
  showModalBottomSheet(
    context: parentContext,
    isScrollControlled: true,
    builder: (BuildContext context){
      return Container(
        padding: EdgeInsets.only(bottom: MediaQuery.of(context).viewInsets.bottm), 
        child: StatefulBuilder(
          builder: (context, setState){
            return Container(
              height: 200,
              child: Column(
                children: [
                  Container(
                    padding: EdgeInsets.only(bottom: 10),
                    child: TextField(
                      autofocus: true,
                      controller: addController,
                    ),
                  ),
                  PopupMenuButton <String>(
                    child:Row(children: [Icon(Icons.repeat), Text('Repeat')], mainAxisAlignment: 
                    MainAxisAlignment.center, mainAxisSize: MainAxisSize.min,)
                    onSelected: (value){
                      setState((){
                        taskRepetition = value;
                      });
                    },
                    itemBuilder: (BuildContext context) {
                      return _pop;
                    }
                  ),
                  Container(
                    padding: EdgeInsets.only(top: 8),
                    child: RaisedButton(
                      child: Text('Select Date'),
                      onPressed: () async {

                      },
                      color: Colors.green,
                    ),
                  ),
                  RaisedButton(
                    child: Text('Add'),
                    onPressed: (){

                    },
                    color: Colors.blueAccent,
                  ),
                ],
              ),
            );
          }
        ),
      );
    }
  );
}