有没有办法获取使用共享首选项保存的特定数据？

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已保存

 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，就像我只想获取 user_id 或 user_email 但我不知道该怎么做我试过这样

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个案：

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

有没有办法获取使用共享首选项保存的特定数据？

is there way to get a particular data which have been saved using shared preference?

flutter

dart

dart-null-safety