C# recursive programming with lists

Question

I am working on a program where each item can hold an array of items (i'm making a menu, which has a tree-like structure)

currently i have the items as a list, instead of an array, but I don't feel like I'm using it to its full potential to simplify code. I chose a list over a standard array because the interface (.add, .remove, etc...) makes a lot of sense.

I have code to search through the structure and return the path of the name (i.e. Item.subitem.subsubitem.subsubsubitem). Below is my code:

public class Item
{
                                                                //public Item[] subitem; <-- Array of Items
    public List<Item> subitem;                                  // <-- List of Items

    public Color itemColor = Color.FromArgb(50,50,200);
    public Rectangle itemSize = new Rectangle(0,0,64,64);
    public Bitmap itemBitmap = null;
    public string itemName;


    public string LocateItem(string searchName)
    {
        string tItemName = null;

        //if the item name matches the search parameter, send it up)
        if (itemName == searchName)
        {
            return itemName;
        }

        if (subitem != null)
        {

            //spiral down a level
            foreach (Item tSearchItem in subitem)
            {
                tItemName = tSearchItem.LocateItem(searchName);

                if (tItemName != null)
                    break;  //exit for if item was found
            }
        }


        //do name logic (use index numbers)
        //if LocateItem of the subitems returned nothing and the current item is not a match, return null (not found)
        if (tItemName == null && itemName != searchName)
        {
            return null;
        }

        //if it's not the item being searched for and the search item was found, change the string and return it up
        if (tItemName != null && itemName != searchName)
        {
            tItemName.Insert(0, itemName + ".");  //insert the parent name on the left -->  TopItem.SubItem.SubSubItem.SubSubSubItem
            return tItemName;
        }

        //default not found
        return null;
    }


}

My question is if there is an easier way to do this with lists? I've been going back and forth in my head as to whether I should use lists or just an array. The only reason I have a list is so that I don't have to make code to resize the array each time I add or remove an item.

Answer 1

Using a list in this case is perfectly acceptable. An array would make a better choice if performance was an issue - if it is, arrays are slightly faster but much less flexible as you've discovered.

One thing that people don't talk about enough is that simplicity is a great basis for structuring code. If it's simpler to write and maintain using lists than arrays, then (all else being equal) using lists is perfectly correct.

Answer 2

Lists sound great. I'd suggest a variation on your definition though. Try creating your class like this:

public class Item : List<Item>
{
    public string Name;
}

If you make Item inherit from List<Item> you automatically make it a tree without requiring the subitem field.

Here's my full version of your class:

public class Item : List<Item>
{
    public string Name;

    private List<Item> LocateItems(string searchName)
    {
        if (this.Name == searchName)
            return (new [] { this }).ToList();

        var result =
            this
                .Select(s => s.LocateItems(searchName))
                .Where(x => x !=null && x.Count > 0)
                .FirstOrDefault();

        if (result != null)
            result.Add(this);

        return result;
    }

    public string LocateItem(string searchName)
    {
        var items = this.LocateItems(searchName);
        if (items == null)
            return null;
        else
            return String.Join(".", items.Select(i => i.Name).Reverse());
    }
}

The method LocateItems returns the list of Item starting with the Item that matched and followed by all of the parent Item instances up to and including the root.

I tested with this code:

var foos = new Item() { Name = "Foo" };
var bars = new Item() { Name = "Bar" };
var qazs = new Item() { Name = "Qaz" };
var wees = new Item() { Name = "Wee" };

foos.Add(bars);
bars.Add(qazs);
foos.Add(wees);

Console.WriteLine(foos.LocateItem("Wee"));
Console.WriteLine(foos.LocateItem("Qaz"));
Console.WriteLine(foos.LocateItem("Bar"));
Console.WriteLine(foos.LocateItem("Foo"));

And I got these results:

Foo.Wee
Foo.Bar.Qaz
Foo.Bar
Foo

Answer 3

I would suggest lists. Since adding/removing items to an array reallocates memory, for a dynamic collection of items (which I assume is your case) lists usually have better performance overall. You might want to take a look at:

Array versus List<T>: When to use which?