Question

I have a project that is using a generic list of a custom class. I have this bound to a grid and I am trying to implement sorting on it. (which is working).

I want to clean my code so I don’t have to do a check for “asc” and “desc” then call either Orderby or OrderByDescending. I would rather set a delegate method at the to of the function and just call OrderMethod, which would already be set to the proper OrderBy… Method.

I can’t seem to get it working.

Here is the delegate that I’ve created. (The class is called ‘FollowingInfo’).

private delegate IOrderedEnumerable<FollowingInfo> OrderMethodDelegate<TSource, TKey>(IEnumerable<FollowingInfo> source, Func<FollowingInfo, string> keySelector);

I’m try to set it as such.

OrderMethodDelegate OrderMethod = FollowList.OrderBy;

But it’s not working…in this example FollowList is of type List(FollowingInfo).

The OrderBy method is an extension method of the generic list class and is defined in Enumerable as such.

public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector);

Any ideas of where I’ve gone wrong?

Answer 1

Define it as:

private delegate IOrderedEnumerable<TSource> Func<TSource, TKey>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector);

You cannot simply override generic method defined in IEnumerable<T> with replacing TSource parameter. It doesn’t know about FollowingInfo class. You can provide your own OrderBy extension method for IEnumerable<FollowingInfo> and use that kind of delegate in it.