Debugging JSON.NET

Question

I'm using JSON.NET to deserialize some JSON returned from a web service. Unfortunately, i'm getting the following err:

Cannot deserialize JSON array into type 'System.Collections.Generic.Dictionary`2[System.String,System.String]'.

but i have no idea how to debug it. is there a way to have it tell me what the offending JSON is? or even what it's trying to deserialize it to? unfortunately this is part of a larger object hierarchy, so it's not just a simple piece of JSON. i've tried stepping through the code, but there's miles of it and little documentation. If it could at least tell me the offending piece, then i can see if maybe i cocked up my object definition or something.

Answer 1

If you want to deserialize what you're converting from json into C# classes there's something built into json.net for this. Just create a settings object and pass it into your deserializeobject call:

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if (!string.IsNullOrEmpty(json))
{
   var settings = new JsonSerializerSettings
       {
           Error = (sender, args) =>
                   {
                       if (System.Diagnostics.Debugger.IsAttached)
                       {
                            System.Diagnostics.Debugger.Break();
                       }
                   }
       };

    result = JsonConvert.DeserializeObject<T>(json, settings);
}

Then when there are errors in the deserialization process (like a mismapped C# class -> json object) it'll break in the debugger. Inspect the args object and you'll see a property called CurrentObject. This is the C# class that the parser is trying to deserialize the JSON into (and will provide details about what the error might be).

Hope that helps.