Question

I am working with a link list. My constructor takes arrays with items in it or appends an item(one at time) to the list through BtnAddTree click. For experimental reasons I am trying to figure out a way to retrieve the position of an item from the list. I have set three buttons that will hopefully show: first, next, last item and display through a label. I created two functions to achieve my need Retrieve and Current_Tree() but here is where I come to a dead end. I am aware to display items that are next I may need to use a loop but unsure how to go about it. How can I display the position of an item found in the list?

        public class ListForTrees
        {

        //Retrieve Position of item
            public void Retrieve(int Position)
            {
                int new_position = Position;
                fruit_trees current = first_tree;

                for (int i = 0; i < Position && current != null; i++)
                {
                    current = current.next_tree;
                }
                return current;
            }

        //Show Current Tree
            public void Current_Tree()
            {
                try
                {
                    current = fruit_trees.first_tree;
                    labelSpecificTree.Text = current.Type.ToString();
                }
                catch { };

            }         



        }

        ListForTrees mainlist = new ListForTrees();     

        private void BtnGo_Click(object sender, EventArgs e)
        {
            fruit_trees[] ax = {   new fruit_trees("cherry", 48, 12.95, 3),
                                             new fruit_trees("pine", 36, 9.95, 8),
                                             new fruit_trees("oak", 60, 14.95, 2),
                                             new fruit_trees("peach", 54, 19.95, 3),
                                             new fruit_trees("pear", 36, 11.85, 2),
                                             new fruit_trees("apple", 62, 13.45, 5)
                                         };   
            mainlist = new ListForTrees(ax);
            fruit_trees current = mainlist.first_tree;   

            while (current != null)
            {
                TxtOutput.AppendText(current.ToString() + Environment.NewLine);
                current = current.next_tree;
            }
        }

        private void ShowNextItem_Click(object sender, EventArgs e)
        {
        //Show Next Item
        }

        private void ShowLastItem_Click(object sender, EventArgs e)
        {
        //Show Last Item
        }

        private void ShowFirstItem_Click_1(object sender, EventArgs e)
        {
        // Show First Item
        }


    }
}

Answer 1

Develop a way to compare the object properly. is tree type unique? maybe you need a full icomparable?

then create a method in the listoftrees class

public int getPosition(fruit_trees tree)
{
 fruit_trees ft = first_tree;
 if(ft.tree_type == tree.tree_type)
 {
      return 0; //or return 1 depending on how you want to index stuff
 }
 int i = 1;//possibly set to 2 if returning 1 above
 while(ft.next_tree != null)
 {
     ft = ft.next_tree;
     if(ft.tree_type == tree.tree_type)
     {
        return i; 
     }
     i++;
 }

 return -1; //or something else here to show that its not in the list

}

also as a side note ..Dont set the label value in the class in the method Current_Tree(). That should return a fruit_trees object and the btn click methods should set the label value .

you should actually just get rid of that method completely(unless there is some reason for it outside of the code above.