反序列化抽象队列< T>在Json [英] Deserializing abstract Queue<T> in Json

问题描述

我有一个抽象类KVP队列。我排队从KVP继承的2个不同的对象。当我序列化队列时，一切正常，但由于KVP无法构造，所以在反序列化时失败。

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.

如果它是一个非通用对象，我可以将其反序列化为动态的，但我不确定如何反序列化可以同时存放事件和ID的队列。

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.

示例代码：

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;
            }

        }

推荐答案

您可以

You could

1. 启用 TypeNameHandling （在序列化和反序列化中）：
   
   

1. Enable TypeNameHandling (in both serialization and deserialization):

    var settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto };
    var serializedText= JsonConvert.SerializeObject(mQueue, settings);

再后来

And then later

    var settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto };
    var mQueue = JsonConvert.DeserializeObject<Queue<T>>(serializedText, settings);

这增加了一个额外的$ type属性到你的多态类，如描述这里。

This adds an extra "$type" property to your polymorphic classes, as is described here.

在选择此解决方案之前，有关使用 TypeNameHandling 讨论可能的安全问题，请参阅 TypeNameHandling在Newtonsoft Json中谨慎使用和如何配置Json.NET以创建易受攻击的Web API 。

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.

编写一个自定义转换器，查看实际属性并选择使用哪个派生类，如下所述：使用json.net反序列化不带类型信息的多态json类。这避免了额外的$ type属性的需求。

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.

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