有没有办法获得使用共享偏好保存的特定数据？

Question

#i 使用共享首选项保存了我所有的用户数据以执行自动登录，并且效果很好，数据被保存

 token = responseData['token'];
      userEmail = responseData['user_email'];
      userNicename = responseData['user_nicename'];
      userDisplayName = responseData['user_display_name'];
      userAddress = responseData['user_address'];
      userContact = responseData['user_contact'];
      userId = responseData['user_id'];
      userDisplayUrl = responseData['user_display_url'];
      notifyListeners();
      SharedPreferences prefs = await SharedPreferences.getInstance();
      final userData = jsonEncode({'token':token,'user_email':userEmail,'user_nicename':userNicename,'user_display_name':userDisplayName,'user_address':userAddress,'user_contact':userContact,'user_id':userId,'user_display_url':userDisplayUrl});
      prefs.setString('userData',userData);

#数据就是这样保存的

{"token":"eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJodHRwczpcL1wvc3dlZXQtYXJkaW5naGVsbGkuMy0xMDgtMTM4LTIwNi5wbGVzay5wYWdlIiwiaWF0IjoxNjQyMzMwNzQyLCJuYmYiOjE2NDIzMzA3NDIsImV4cCI6MTY0MjkzNTU0MiwiZGF0YSI6eyJ1c2VyIjp7ImlkIjoiMjgifX19.2jZEu-QNL3UxRiFSgVE728bF_cl_CZd0VJLT1f5HfCc","user_email":"sauravadhikari404@gmail.com","user_nicename":"sauravadhikari404","user_display_name":"SauravAdhikari404","user_address":null,"user_contact":null,"user_id":"28","user_display_url":""}

#现在我想访问单个数据，例如我只想获取该 user_id 或 user_email，但我不知道该怎么做，我尝试过这样

String? userData;
  @override

  void initState(){
    // TODO: implement initState
    getUserId();
    super.initState();
  }
  void getUserId()async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      userData = prefs.getString("userData");
      print(userData);
    });
  }

#正如我上面提到的，我的所有数据都在 userData 中，但现在我只想获取我的 user_id 或 user_email，但我无法

Answer 1

使用 jsonDecode 将其转换为 Map：

像这样：

setState(() {
  var userId = jsonDecode(prefs.getString("userData"))["user_id"];
  print(userId);
});

处理null 案例：

String? userDataString = prefs.getString("userData");
if(userDataString != null){
  var userId = jsonDecode(userDataString)["user_id"];
  var email = jsonDecode(userDataString)["user_email"];
}