Can I use reflection to shorten this code?

Question

I have some code that I feel like I should be able to shorten incredibly, but I can't figure out how to do it.

I have a base class called Message and may classes that derive from it.

namespace ModalVR {
    public class Message {
        public string message;

        public Message() {
            this.message = this.ToString();
        }
    }
}

The subclasses get converted to JSON, and I have a function that receives this JSON and I need to create the appropriate class. However the function that does it has a huge case statement and I feel that there must be a better way of doing this. This is what that function looks like.

public Message ConstructMessageFromJSON(string JSON) {
    string messageName = JsonUtility.FromJson<Message>(JSON).message;

    Message derivedMessage = null;

    switch(messageName) {
        case "ModalVR.GetBatteryInfo": {
            derivedMessage = JsonUtility.FromJson<GetBatteryInfo>(JSON);
            break;
        }

        case "ModalVR.GetBatteryInfoResponse": {
            derivedMessage = JsonUtility.FromJson<GetBatteryInfoResponse>(JSON);
            break;
        }

        // Many more case statements snipped out

        default: {
            LogManager.Log("Received unknown message of " + messageName, LogManager.LogLevel.Error);
            break;
        }
    }

    return derivedMessage;
}

Is there any way I can replace this huge case statement with something simpler?

Thanks in advance John Lawrie

This may be helpful. https://stackoverflow.com/questions/36239705/serialize-and-deserialize-json-and-json-array-in-unity — hatchet - done with SOverflow, May 25 '17 at 18:25
This really seems like a case for a virtual function. You're switching on the type to do something that differs only in the type you just switched on. — 15ee8f99-57ff-4f92-890c-b56153, May 25 '17 at 18:33

score 1 · Accepted Answer · answered May 25 '17 at 18:52

1

Using reflection only, you can do:

string messageName = "ModalVR.GetBatteryInfo";
Type messageType = Assembly.GetAssembly(typeof(Message)).GetType(messageName);
Message derivedMessage = (Message)JsonUtility.FromJson(json, messageType);

It retrieves the Assembly in which you have defined your Message class and then search for the requested type in this assembly.

answered May 25 '17 at 18:52

Arnaud Develay

3,920
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This is exactly what I needed. It is the best solution since it deals with the addition of more messages without requiring any additional code. Thanks – Dalanchoo May 25 '17 at 19:11

score 0 · Answer 2 · answered May 25 '17 at 18:25

The easiest way would be to create a dictionary like that:

    var typeMatches = new Dictionary<string, Type>
    {
        {"ModalVR.GetBatteryInfo", typeof(GetBatteryInfo)}
    };

and then just get the value from it: (that's C# 7)

    if (!typeMatches.TryGetValue(messageName, out var messageType))
    {
        LogManager.Log("Received unknown message of " + messageName, LogManager.LogLevel.Error);
        return;
    }

    var derivedMessage = (Message) JsonUtility.FromJson(JSON, messageType);

Can I use reflection to shorten this code?

2 Answers2