c# Trying to reverse a list

Question

public class CategoryNavItem
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string Icon { get; set; }

    public CategoryNavItem(int CatID, string CatName, string CatIcon)
    {
        ID = CatID;
        Name = CatName;
        Icon = CatIcon;
    }
}

public static List<Lite.CategoryNavItem> getMenuNav(int CatID)
{
    List<Lite.CategoryNavItem> NavItems = new List<Lite.CategoryNavItem>();

    -- Snipped code --

    return NavItems.Reverse();
}

The reverse doesn't work:

Error 3 Cannot implicitly convert type 'void' to 'System.Collections.Generic.List<Lite.CategoryNavItem>'

Any ideas why this might be?

Answer 1

Try:

NavItems.Reverse();
return NavItems;

List<T>.Reverse() is an in-place reverse; it doesn't return a new list.

This does contrast to LINQ, where Reverse() returns the reversed sequence, but when there is a suitable non-extension method it is always selected in preference to an extension method. Plus, in the LINQ case it would have to be:

return someSequence.Reverse().ToList();

Answer 2

One workaround would be Return NavItems.AsEnumerable().Reverse();

Answer 3

.Reverse() on a list reverses the items within the list, it does not return a new reversed list.

Answer 4

Reverse() does not returns reversed list itself, it modifies original list. So rewrite it as following:

return NavItems.Reverse(); 

TO

NavItems.Reverse(); 
return NavItems;

Answer 5

Reverse() does not return a List as expected of your function.

NavItems.Reverse();
return NavItems;

Answer 6

.Reverse reverses the "in-place"..., try

NavItems.Reverse();
return NavItems;

Answer 7

If you have a list like in your example:

List<Lite.CategoryNavItem> NavItems

You can use the generic Reverse<> extensions method to return a new list without modifiying the original one. Just use the extension method like this:

List<Lite.CategoryNavItem> reversed = NavItems.Reverse<Lite.CategoryNavItem>();

Notes: You need to specify the <> generic tags to explicit use the extension method. Don't forget the

using System.Linq;