Problems deserializing using Newtonsoft JSON

Question

I have the following class:

public class Student
{
    public int studentNumber;
    public string testWeek;
    public string topics;
}

I do some stuff to it, serialize it and save it in a file. It looks likes this:

[
  {
    "studentNumber": 1,
    "testWeek": "1",
    "topics": "5 & 8"
  },
  {
    "studentNumber": 2,
    "testWeek": "1",
    "topics": "5 & 8"
  },
  {
    "studentNumber": 3,
    "testWeek": "1",
    "topics": "5 & 8"
  },
  {
    "studentNumber": 4,
    "testWeek": "1",
    "topics": "5 & 8"
  },
  {
    "studentNumber": 5,
    "testWeek": "1",
    "topics": "5 & 8"
  }
]

Later I want to deserialize it so I can work on it again. I have this code

Student[] arr = new Student[numberOfStudentsInClass];
arr = JsonConvert.DeserializeObject<Student>(File.ReadAllText(_selectedClass))

Where _selectedClass is string containing the file name. But I am getting an error

Cannot convert WindowsFormApplicationsForm1.Form.Student to WindowsFormApplicationsForm1.Form.Student[]

mason · Accepted Answer · 2016-04-15 02:41:51Z

4

You indicated in your JsonConvert.DeserializeObject that you are trying to deserialize to a single Student instance. Not an array. And there's no need to initialize the array in one statement and then assign it a value on another. And anyways, we generally use generic arrays these days.

Replace:

Student[] arr = new Student[numberOfStudentsInClass];
arr = JsonConvert.DeserializeObject<Student>(File.ReadAllText(_selectedClass))

With this:

List<Student> students = 
     JsonConvert.DeserializeObject<List<Student>>(File.ReadAllText(_selectedClass));

answered Apr 15, 2016 at 2:41

mason

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1 Comment

Luves2spooge Over a year ago

Thank you. I'd previously been working on the data as an array but maybe as a list might be better. Time to start rewriting!

sm_ · Accepted Answer · 2016-04-15 04:04:45Z

3

As the exception states, the method JsonConvert.DeserializeObject<Student> returns an object of type Student, while the variable arr is of type Student[] .so you can't assign the result of JsonConvert.DeserializeObject<Student> to arr.

you need to Deserialize your text to a List<Student> instead and call .ToArray if you want an array such as follows:

Student[] students = JsonConvert.DeserializeObject<List<Student>>(File.ReadAllText(_selectedClass)).ToArray();

answered Apr 15, 2016 at 4:04

sm_

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