deserializing json C# “First chance exception of type - newtonsoft”

问题

I am trying to save and load files from isolatedStorage based on this class by forum member Shawn Kendrot that i got throughout this forum post.

I’m able to save with no problem but when loading then deserialising the json file I am getting an error

“A first chance exception of type 'Newtonsoft.Json.JsonSerializationException' 
occurred in Newtonsoft.Json.DLL”

I don’t know what I could be doing wrong, because the file is saved and it’s reading properly but not deserializing. The json file has 4 entries at the moment, but it will have 6 later on.

Can anyone help me understand what is wrong here?

It's this function:

public static T ReadSharedData<T>(string fileName) where T : class, new()
    {
        T result = new T();
        var mutex = GetMutex(fileName);
        mutex.WaitOne();
        fileName = GetSharedFileName(fileName);
        try
        {
            var storage = IsolatedStorageFile.GetUserStoreForApplication();
            if (storage.FileExists(fileName))
            {
                using (var fileStream = storage.OpenFile(fileName, FileMode.Open, FileAccess.Read))
                {
                    using (var reader = new StreamReader(fileStream))
                    {
                        string json = reader.ReadToEnd();
                        if (string.IsNullOrEmpty(json) == false)
                        {
                            var data = JsonConvert.DeserializeObject<T>(json);
                            if (data != null)
                            {
                                result = data;
                            }
                        }
                    }
                }
            }
        }
        catch { }
        finally
        {
            mutex.Release();
        }
        return result;
    }

The problem is occurring on this line:

var data = JsonConvert.DeserializeObject<T>(json);

My MainPage.xaml.cs

using Microsoft.Phone.Shell;
using JSON_Storage_Test.Resources;
using System.Diagnostics;
using System.Text;
using System.IO.IsolatedStorage;

namespace JSON_Storage_Test
{
public partial class MainPage : PhoneApplicationPage
{
    private const string FileName = “movieSettings.json";

    // Constructor
    public MainPage()
    {
        InitializeComponent();
    }

    private void SaveJ_Click(object sender, RoutedEventArgs e)
    {
        string json = @"{
                          'Name': 'Bad Boys',
                          'ReleaseDate': '1995-4-7T00:00:00',
                          'Genres': [ 'Action', 'Comedy' ]
                        }";

        FileStorage.WriteSharedData("movieSettings.json", json);
    }

    //Im not sure here, what should the return type be
    //and how would i then access the retrieved data
    private void LoadJ_Click(object sender, RoutedEventArgs e)
    {
        FileStorage.ReadSharedData<MainPage>(FileName);
        Debug.WriteLine("Load clicked");
    }
  }
}

回答1:

Your problem is - as you pointed out by yourself - you have no clue what to do with the return value.

FileStorage.ReadSharedData<MainPage>(FileName); tries to parse your json string to an object of type MainPage which should have the properties Name, ReleaseDate and Genres (which should be an IEnumerable).

Your MainPage actually has no such properties, so your deserialization crashes.

Try the following:

public class Move
{
    public string Name;
    public string ReleaseDate;
    public IEnumerable<string> Genres
}

And then call var deserializedMove = FileStorage.ReadSharedData<Movie>(FileName);

来源：https://stackoverflow.com/questions/21596564/deserializing-json-c-sharp-first-chance-exception-of-type-newtonsoft