Question

Hi guys got a wired problem (well I find it a wired problem :P)

I have an order page done in asp.net c#, and which a user adds ingredients to a set of list boxes, once the user and finished adding items, they get combined to make a sandwich then added to another list box that shows the sandwiches and their ingredients. I also have a button to allow the user to remove the highlighted sandwich from the order, this all works fine until the page loads up with a query string that skips the adding of ingredients and just shows the sandwiches on a order, the listbox of sandwiches populates fine but I then get an error when the remove button is clicked which is

System.NullReferenceException: Object reference not set to an instance of an object.

on
CompletedSandwiches.SelectedItem.Text

the only difference is that I pass a query string “?EDIT=1”

and then on page_load I check

        if (!Page.IsPostBack)
        {
            if ((Request.QueryString["EDIT"] != null) && (Request.QueryString["EDIT"] == "1"))
            {

                GetCurrentSandwiches();
            }

            RemoveFilling.Enabled = false;
            RemoveCondiment.Enabled = false;
            CID = int.Parse(Session["CID"].ToString());

        }

GetCurrentSandwiches does the following:

 protected void GetCurrentSandwiches()
        {
            sandwichOnOrder.Clear();

            OrderManagement order = new OrderManagement();

            List<SarnieIngredients> bob = order.GetSandwichesOnOrder(int.Parse(Session["OID"].ToString()));
            List<int> ingredientIDs = new List<int>();


            foreach (SarnieIngredients sarnie in bob)
            {
                List<Ingredients> batchOfIngredients = new List<Ingredients>();
                double amount = 0.00;
                ingredientIDs = sarnie.IngredientIDs;
                foreach (int i in ingredientIDs)
                {
                    Ingredients contents =  ingredient.GetDesiredIngredientByID(i);

                    batchOfIngredients.Add(contents);
                    amount += contents.Price;
                }

                SandwichConentent sandwich = new SandwichConentent(batchOfIngredients, amount);
                sandwichOnOrder.Add(sandwich);

                CompletedSandwiches.Items.Add(sandwich.ToString());

            } 

and my remove buttons code does

        bool found = false;
        int i = 0;

        while (i < sandwichOnOrder.Count || found == false)
        {


            SandwichConentent content = sandwichOnOrder[i];
            if (content.ToString() == CompletedSandwiches.SelectedItem.Text)
            {
                CompletedSandwiches.Items.Remove(CompletedSandwiches.SelectedItem);
                sandwichOnOrder.Remove(content);
                found = true;
            }
        }

does anyone have any idea why I am having this problem?

thanks in advance Matt

edit ~ sorry I forgot to mention I know I haven’t put validation in but I check manually that there’s a item selected before I pass and when looking at the listbox in debug it is apparently null even though visually it is not.

edit 2 ~ sorry again the error occurs on this line

if (content.ToString() == CompletedSandwiches.SelectedItem.Text)

and when ?EDIT=1 is passed, it is a new page call from the main page of the web app

Answer 1

You need one if in your remove method:

if (CompletedSandwiches.SelectedItem.Text != null)
 ...