Are there any examples of custom JSON converters for MvvmCross

1. Implementing Custom JSON Converters

Custom JSON converters in MvvmCross can be created by deriving from `JsonConverter` or `JsonConverter`, similar to how it's done in standard .NET applications using Newtonsoft.Json. However, MvvmCross uses an older PCL version of Newtonsoft.Json (4.5.4.14825), so ensure compatibility when implementing custom converters.

Here's an example of a custom converter for a hypothetical `Temperature` struct:

csharp
using Newtonsoft.Json;

public struct Temperature
{
    public int Degrees { get; }
    public bool IsCelsius { get; }

    public Temperature(int degrees, bool celsius)
    {
        Degrees = degrees;
        IsCelsius = celsius;
    }

    public override string ToString() => $"{Degrees}{(IsCelsius ? "C" : "F")}";
    public static Temperature Parse(string input)
    {
        int degrees = int.Parse(input.Substring(0, input.Length - 1));
        bool celsius = input.Substring(input.Length - 1) == "C";
        return new Temperature(degrees, celsius);
    }
}

public class TemperatureConverter : JsonConverter
{
    public override Temperature ReadJson(JsonReader reader, Type objectType, Temperature existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        return Temperature.Parse((string)reader.Value);
    }

    public override void WriteJson(JsonWriter writer, Temperature value, JsonSerializer serializer)
    {
        writer.WriteValue(value.ToString());
    }
}

2. Using Custom Converters in MvvmCross

To use custom converters in MvvmCross, you can add them to the `JsonSerializerSettings` used by the `IMvxJsonConverter`. However, since MvvmCross uses a specific version of Newtonsoft.Json, ensure that your custom converters are compatible.

Here's how you might use the custom converter in serialization:

csharp
public class ExampleObject
{
    public string Name { get; set; }
    public Temperature Temperature { get; set; }
}

public class MyViewModel : MvxViewModel
{
    private readonly IMvxJsonConverter _jsonConverter;

    public MyViewModel(IMvxJsonConverter jsonConverter)
    {
        _jsonConverter = jsonConverter;
    }

    protected override void SaveStateToBundle(IMvxBundle bundle)
    {
        var exampleObject = new ExampleObject
        {
            Name = "John Doe",
            Temperature = new Temperature(25, true)
        };

        var jsonSettings = new JsonSerializerSettings
        {
            Converters = new List { new TemperatureConverter() }
        };

        // MvvmCross uses its own serialization internally, so you might need to manually serialize with custom settings.
        var jsonText = JsonConvert.SerializeObject(exampleObject, jsonSettings);

        bundle.Data["ExampleObject"] = jsonText;
    }
}

3. Implementing IMvxJsonConverter

If you need more control over serialization and deserialization, you can implement your own `IMvxJsonConverter` interface. This allows you to customize the serialization process entirely.

csharp
public class CustomMvxJsonConverter : IMvxJsonConverter
{
    public string SerializeObject(object toSerialise)
    {
        var jsonSettings = new JsonSerializerSettings
        {
            Converters = new List { new TemperatureConverter() }
        };
        return JsonConvert.SerializeObject(toSerialise, jsonSettings);
    }

    public T DeserializeObject(string inputText)
    {
        var jsonSettings = new JsonSerializerSettings
        {
            Converters = new List { new TemperatureConverter() }
        };
        return JsonConvert.DeserializeObject(inputText, jsonSettings);
    }

    public object DeserializeObject(Type type, string inputText)
    {
        var jsonSettings = new JsonSerializerSettings
        {
            Converters = new List { new TemperatureConverter() }
        };
        return JsonConvert.DeserializeObject(inputText, type, jsonSettings);
    }
}

Conclusion

While MvvmCross primarily uses Newtonsoft.Json for serialization, creating custom JSON converters is straightforward and can be integrated into your MvvmCross applications by implementing `JsonConverter` or `IMvxJsonConverter`. Ensure compatibility with the version of Newtonsoft.Json used by MvvmCross.