Get methodinfo for Enumerable.DefaultIfEmpty

问题:

I'm building some Linq Expression and trying to get hold of MethodInfo for IEnumerable.DefaultIfEmpty (http://msdn.microsoft.com/en-us/library/bb360179.aspx). What seemed to be an easy task but I'm clueless to why it's not working.

typeof(Enumerable).GetMethod("DefaultIfEmpty", new[] { typeof(IEnumerable<>) });

typeof(Enumerable).GetMethod("DefaultIfEmpty", new[] { typeof(IEnumerable<>).MakeGenericType(typeof(WorkitemListModel)) });

回答1:

Getting generic methods is a pain, to be honest. I don't know of a better way than to use:

var method = typeof(Enumerable).GetMethods()
                               .Where(m => m.Name == "DefaultIfEmpty")
                               .Where(m => m.GetParameters().Length == 1)
                               .Single();

To call GetMethod, you'd have to have the exact correct parameter type, including the right generic type parameter for the parameter. Once you've got that once you could do it, but until then I think the above is all that's available :(