如何在 OnChanged

如何解决如何在 OnChanged

我有一个 DropdownButtonFormField，其中最后一项是 DropdownMenuItem，用于使用对话框添加新对象。

Padding(
  padding: const EdgeInsets.only(bottom: 15),child: Observer(
    builder: (_){
      return DropdownButtonFormField(
        value: createdContentStore.subjectTitleSelected,isDense: true,decoration: Inputdecoration(
            contentPadding: EdgeInsets.symmetric(horizontal: 10,vertical: 10),border: OutlineInputBorder()
        ),onChanged: (value) async {
          // print(value);
          if(value == 'newSubject'){
            Subject newSubject = await showDialog(
                context: context,builder: (_) => CreatedSubjectDialogBox(isNewContent: true,)
            );
            if(newSubject != null){
              createdContentStore.setSubjectTitleSelected(newSubject.title);
              createdContentStore.setSubject(newSubject);
            } else {
              // WHAT CAN I DO HERE TO RESET DROP'S VALUE?
            }
          } else {
              createdContentStore.setSubjectTitleSelected(value);
          }
        },iconSize: 30,hint: Text('Selecione uma matéria'),items: subjectStore.subjectList.map((subject) => DropdownMenuItem(
          value: subject.title,child: Text(subject.title),onTap: () {
            createdContentStore.setSubject(subject);
          },)).toList()..add(DropdownMenuItem(
          value: 'newSubject',child: Center(
            child: Text(
              'Nova Matéria'.toupperCase(),style: TextStyle(color: redRevise),),)),);
    },);

当对话框显示时，用户可以创建一个将出现在下拉列表中的新对象。当用户取消对话框时，它会显示最后一个项目。所需的行为是显示提示。

有人可以帮我吗？ 谢谢！

解决方法

您所要做的就是从下拉列表中删除值，

 DropdownButtonFormField(
//** REMOVE THE VALUE **
        isDense: true,decoration: InputDecoration(
            contentPadding: EdgeInsets.symmetric(horizontal: 10,vertical: 10),isDense: true,border: OutlineInputBorder()
        ),onChanged: (value) async {
          if(value == 'newSubject'){
            Subject newSubject = await showDialog(
                context: context,builder: (_) => CreatedSubjectDialogBox(isNewContent: true,)
            );
            if(newSubject != null){
              createdContentStore.setSubjectTitleSelected(newSubject.title);
              createdContentStore.setSubject(newSubject);
            } else {
              // WHAT CAN I DO HERE TO RESET DROP'S VALUE?
            }
          } else {
              createdContentStore.setSubjectTitleSelected(value);
          }
        },iconSize: 30,hint: Text('Selecione uma matéria'),items: subjectStore.subjectList.map((subject) => DropdownMenuItem(
          value: subject.title,child: Text(subject.title),onTap: () {
            createdContentStore.setSubject(subject);
          },)).toList()..add(DropdownMenuItem(
          value: 'newSubject',child: Center(
            child: Text(
              'Nova Matéria'.toUpperCase(),style: TextStyle(color: redRevise),),)),);
    },);