EmptyCollectionContractResolver

EmptyCollectionContractResolver.cs

class EmptyCollectionContractResolver : DefaultContractResolver {
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization) {
        JsonProperty property = base.CreateProperty(member, memberSerialization);

        Predicate<object> shouldSerialize = property.ShouldSerialize;
        property.ShouldSerialize = obj => (shouldSerialize == null || shouldSerialize(obj)) && !IsEmptyCollection(property, obj);
        return property;
    }

    private bool IsEmptyCollection(JsonProperty property, object target) {
        var value = property.ValueProvider.GetValue(target);
        var collection = value as ICollection;
        if (collection != null && collection.Count == 0)
            return true;

        if (!typeof(IEnumerable).IsAssignableFrom(property.PropertyType))
            return false;

        var countProp = property.PropertyType.GetProperty("Count");
        if (countProp == null)
            return false;

        var count = (int)countProp.GetValue(value, null);
        return count == 0;
    }
}