Question

I am currently working/experimenting with lists. I am able to determine with function GetNextTree the position of each item in my list such as: First, Next and Last. I have an already made list from an array ax but now I am trying to implement an insert button that will take values tree_type, tree_height, tree_price, tree_instock and create the item. Since I can point anywhere in my list, the insert will be intended to add an item after the currently pointed to item. That is where my question is: How can I add a new item after the currently pointed to item?

public class fruit_trees
{
    private string tree_type = " ";
    private int tree_height = 0;
    public double tree_price = 0;
    private int tree_instock = 0;


    public fruit_trees next_tree;

    public fruit_trees(string newtree, int newheight, double newprice, int newinstock)
    {
        tree_type = newtree;
        tree_height = newheight;
        tree_price = newprice;
        tree_instock = newinstock;


        next_tree = null;
    }

    public string GetTreeType
    {
        get { return tree_type;
            }
    }

    public override string ToString()
    {
        return tree_type + " " + tree_height + " " + tree_price + " " + tree_instock;

    }

}

public class ListForTrees
{
    private fruit_trees first_tree;
    public fruit_trees First_tree
    {
        get
        {
            return first_tree;
        }
    }

    public fruit_trees last_tree;
    public int current;
    public int count = 0;



    public ListForTrees(fruit_trees new_tree)
    {
        first_tree = new_tree;
        last_tree = new_tree;
        count = 1;
        current = 0;
    }

    public ListForTrees(IEnumerable trees)
    {
        current = 0;
        foreach (fruit_trees t in trees)
        {
            this.AddTree(t);
        }
    }

    public fruit_trees GetNextTree()
    {
        //current = 0;
        fruit_trees ft = first_tree;

        if (current == count)
        {

            current = 0;
        }

        int i = 0;
        while (i != current)
        {
            ft = ft.next_tree;
            i++;

        }

        return ft;
    }

}

ListForTrees mainlist = new ListForTrees();
private void BtnInsertTree_Click(object sender, EventArgs e)
{

    try
    {
        int height = Convert.ToInt32(TxtTreeHeight.Text);
        int stock = Convert.ToInt32(TxtTreeStock.Text);
        double price = Convert.ToDouble(TxtTreePrice.Text);

        fruit_trees treeadd = new fruit_trees(TxtTreeName.Text, height, price, stock);
        mainlist.AddTree(treeadd);

    }
    catch
{
    MessageBox.Show("Please check intput fields");
    }
}

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 ShowFirstItem_Click(object sender, EventArgs e)
{
    //Show Next Item
    labelSpecificTree.Text = mainlist.First_tree.GetTreeType;
}

private void ShowNextItem_Click(object sender, EventArgs e)
{

    fruit_trees obj = mainlist.GetNextTree();
    if (obj.next_tree == null)
    {
        labelSpecificTree.Text = mainlist.First_tree.GetTreeType.ToString();
    }
    else
    {
        mainlist.current++;
        labelSpecificTree.Text = obj.next_tree.GetTreeType.ToString();
    }

}

private void ShowLastItem_Click(object sender, EventArgs e)
{
    // Show First Item
    labelSpecificTree.Text = mainlist.last_tree.GetTreeType;

}

Answer 1

So I’m slightly confused by what’s going on here. You’re implementing your own ArrayList like class which is not really a list at all… I don’t really see the point of doing such things in C# but alright… Here’s the method;

  fruit_trees[] InsertNode(fruit_trees current, fruit_trees nNode)
  {
       fruit_trees[] temp = new fruit_trees[ax.Length + 1];
       int i = 0;

       while (ax[i] != current)
       {
             temp[i] = ax[i];
             i++;
       }
       temp[i+1] = nNode;
       while (i < ax.Length)
       {
            temp[i+1] = ax[i];
       }

       return temp; 
  }

call this like such;

  ax = InsertNode(current, nNode);

What we’re doing is making a new list with one extra slot, copying each fruit_tree over til we hit the node we want to insert after, then we copy the new tree in. After that we copy over the rest of the old array. Then we return the new array.