How do I implement custom error handling for Newtonsoft.Json in MvvmCross

1. Custom JSON Converter for Error Handling**

Newtonsoft.Json allows you to create custom converters to handle serialization and deserialization of specific types, including exceptions. This can be particularly useful for controlling how errors are represented in JSON.

csharp
using Newtonsoft.Json;
using System;

public class CustomExceptionConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Exception);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        // Handle deserialization of exceptions here
        // For simplicity, let's assume we're just returning the original exception
        var json = JObject.Load(reader);
        var className = json["ClassName"].ToString();
        var message = json["Message"].ToString();
        return new Exception(message);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var ex = (Exception)value;
        writer.WriteStartObject();
        writer.WritePropertyName("ClassName");
        writer.WriteValue(ex.GetType().Name);
        writer.WritePropertyName("Message");
        writer.WriteValue(ex.Message);
        // Add any other properties you want to include
        writer.WriteEndObject();
    }
}

2. Handling Deserialization Errors**

When deserializing JSON, you might encounter errors if the data is malformed or doesn't match the expected types. You can handle these errors by using the `Error` event in `JsonSerializerSettings`.

csharp
var settings = new JsonSerializerSettings
{
    Error = (sender, args) =>
    {
        // Handle the error here
        args.ErrorContext.Handled = true; // Prevents the error from bubbling up
        // You can log the error or throw a custom exception
    }
};

try
{
    var deserializedObject = JsonConvert.DeserializeObject(jsonString, settings);
}
catch (Exception ex)
{
    // Handle any exceptions that weren't handled by the Error event
}

3. Integrating with MvvmCross**

In MvvmCross, you can integrate this custom error handling into your view models by using a base view model class that handles errors centrally. This approach allows you to manage errors across your application uniformly.

csharp
public class BaseViewModel : MvxViewModel
{
    public void HandleError(Exception ex)
    {
        // Centralized error handling logic
        // You can use the custom converter here if needed
        var errorJson = JsonConvert.SerializeObject(ex, new CustomExceptionConverter());
        // Display or log the error
    }
}

public class MyViewModel : BaseViewModel
{
    public IMvxCommand MyCommand { get; private set; }

    public MyViewModel()
    {
        MyCommand = new MvxCommand(() =>
        {
            try
            {
                // Code that might throw an exception
            }
            catch (Exception ex)
            {
                HandleError(ex);
            }
        });
    }
}

4. Using MvvmCross Plugins for JSON Handling**

MvvmCross provides a JSON plugin that wraps Newtonsoft.Json, allowing you to serialize and deserialize objects easily. You can configure this plugin to use your custom converters.

csharp
var serializer = Mvx.IoCProvider.Resolve();
// Use the serializer with your custom converter
var json = serializer.SerializeObject(myObject, new JsonSerializerSettings
{
    Converters = { new CustomExceptionConverter() }
});

By following these steps, you can implement robust custom error handling for Newtonsoft.Json in your MvvmCross application, ensuring that errors are handled consistently and elegantly across your app.