Serialize dictionary as array (of key value pairs)

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Another way to accomplish this is to use a custom ContractResolver. That way you do not have to subclass Dictionary<K,V> nor apply a transform each time you serialize, as suggested in other answers.

The following resolver will cause ALL dictionaries to be serialized as an array of objects with “Key” and “Value” properties:

class DictionaryAsArrayResolver : DefaultContractResolver
{
    protected override JsonContract CreateContract(Type objectType)
    {
        if (objectType.GetInterfaces().Any(i => i == typeof(IDictionary) || 
           (i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IDictionary<,>))))
        {
            return base.CreateArrayContract(objectType);
        }

        return base.CreateContract(objectType);
    }
}

To use the resolver, add it to your JsonSerializerSettings, then pass the settings to JsonConvert.SerializeObject() like this:

JsonSerializerSettings settings = new JsonSerializerSettings();
settings.ContractResolver = new DictionaryAsArrayResolver();

string json = JsonConvert.SerializeObject(obj, settings);

Here is a working demo.

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