Question

I have a assignment from school and I’m almost finished, only one thing left. I get a NullReferenceException every time I start the program. Everything works as it’s supposed to except for the listview where the exception is thrown.

This is from the MainForm:

private void UpdateListView()
{
    lstReservations.Clear();

    string[] seats = new string[m_seatMngr.GetSeatInfoStrings((SeatManager.DisplayOption)cmboBoxListAlternitives.SelectedIndex, out seats)];

    if (seats != null && seats.Length > 0)
    {
        string[] split = new string[4];

        for (int i = 0; i < seats.Length; i++)
        {
            split = seats[i].Split('|');

            ListViewItem newItem = new ListViewItem(split[0]);
            newItem.SubItems.Add(split[1]);
            newItem.SubItems.Add(split[2]);
            newItem.SubItems.Add(split[3]);
            //Lägger till newItem till lstReservations
            lstReservations.Items.Add(newItem);
        }
    }
}

It’s this line that throws the exception:

seats[i].Split('|');

Here’s the method GetSeatInfoString from the SeatManager class:

public int GetSeatInfoStrings(DisplayOption choice, out string[] strSeatInfoStrings)
{
    strSeatInfoStrings = null;
    int count = GetNumOfSeats(choice);

    if (count <= 0)
    {
        return 0;
    }

    strSeatInfoStrings = new string[count];

    int i = 0; //counter for return array
    //Is the element corresponding with the index empty
    for (int index = 0; index < m_totNumOfSeats; index++)
    {
        switch (choice)
        {
            case DisplayOption.AllSeats:
                strSeatInfoStrings[index] = GetSeatInfoAt(index);
                i++;
                break;
            case DisplayOption.ReservedSeats:
                if (m_nameList[index] != null)
                {
                    strSeatInfoStrings[i] = GetSeatInfoAt(index);

                    i++;
                }
                break;
            case DisplayOption.VacantSeats:
                if (m_nameList[index] == null)
                {
                    strSeatInfoStrings[i] = GetSeatInfoAt(index);

                    i++;
                }
                break;
            default:
                break;
        }
    }

    return i;
}

I know what a NullReferenceException is but I can’t find why I get it. The array seats should be filled, if that’s the problem what’s wrong in the method GetSeatInfoString?

Answer 1

This line:

string[] seats = new string[m_seatMngr.GetSeatInfoStrings((SeatManager.DisplayOption)
    cmboBoxListAlternitives.SelectedIndex, out seats)];

The order is unclear, but there are two assignments to seats here – The first via the out, the second with all nulls (a new string-array). Try instead:

string[] seats;
m_seatMngr.GetSeatInfoStrings((SeatManager.DisplayOption)
    cmboBoxListAlternitives.SelectedIndex, out seats);

Which only assigned via the “out”.