Deserializing abstract Queue in Json

Question

I have a Queue of an abstract class KVP. I queue 2 different objects which inherit from KVP. Everything works fine when I serialize the queue, but since KVP cannot be constructed it fails on deserialization.

If it was a single non generic object I could deserialize as dynamic, but I'm not sure how to deserialize a queue that could hold both events and IDs.

Sample code:

public virtual async Task<bool> LoadFromFile(string FileName, bool addToExistingQueue,bool DeleteFileAfterLoad = true)
        {
            try
            {
                IFile File = await PCLStorage.FileSystem.Current.LocalStorage.GetFileAsync(FileName);
                var serializedText = await File.ReadAllTextAsync();
                var mQueue = JsonConvert.DeserializeObject<Queue<T>>(serializedText,jss);
                if (!addToExistingQueue)
                {
                    _queue = new ConcurrentQueue<T>();
                }
                while (mQueue.Count > 0)
                {
                    _queue.Enqueue(mQueue.Dequeue());
                }




                if (DeleteFileAfterLoad)
                {
                    await File.DeleteAsync();
                }
                return true;

            }
            catch (Exception ex)
            {
                Debug.WriteLine("Could not load File. Exception Message: " + ex.Message);
                return false;
            }

        }
        public virtual async Task<bool> WriteToFile(string FileName)
        {
            try
            {
                Debug.WriteLine("Writing File: " + FileName);
                var File = await FileSystem.Current.LocalStorage.CreateFileAsync(FileName, CreationCollisionOption.ReplaceExisting);
                var serializedText = JsonConvert.SerializeObject(_queue.ToList(),jss);
                await File.WriteAllTextAsync(serializedText);
                return true;
            }
            catch (Exception ex)
            {
                Debug.WriteLine("Could not write File with exception message: " + ex.Message);
                return false;
            }

        }

Could you post some sample json with your question to give us a better idea? — olitee, Mar 23 '15 at 15:49
@Liam yes it doesnt matter as its a abstract class that i made. — Mr. MonoChrome, Mar 23 '15 at 15:50
I just found TypeNameHandling in a separate post. http://stackoverflow.com/questions/20038441/deserialize-a-listabstractclass-with-newtonsoft-json — Mr. MonoChrome, Mar 23 '15 at 15:51

dbc · Accepted Answer · 2017-11-17T17:56:10.180

You could

Enable TypeNameHandling (in both serialization and deserialization):
```
    var settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto };
    var serializedText= JsonConvert.SerializeObject(mQueue, settings);
```
And then later
```
    var settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto };
    var mQueue = JsonConvert.DeserializeObject<Queue<T>>(serializedText, settings);
```
This adds an extra "$type" property to your polymorphic classes, as is described here.

Before choosing this solution, for a discussion of possible security concerns using TypeNameHandling, see TypeNameHandling caution in Newtonsoft Json and How to configure Json.NET to create a vulnerable web API.
Write a custom converter that looks at the actual properties and chooses which derived class to use, as is discussed here: Deserializing polymorphic json classes without type information using json.net. This avoids the need for the extra "$type" property.

score 0 · Answer 2 · edited Mar 23 '15 at 16:10

0

This should work if you use the following setting in the JSON.NET serialiser settings:

var settings = new JsonSerializerSettings {TypeNameHandling = TypeNameHandling.Auto};

This will encode the object type into the JSON stream, which will help the deserializer determined the specific object type to construct during de-serialization.

edited Mar 23 '15 at 16:10

Liam

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answered Mar 23 '15 at 15:53

olitee

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Deserializing abstract Queue in Json

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