Question

I have been up half the night and still trying to get this null exception figured out. I have read a few of texts about this issue but none has helped me in any way, to me what the problem is as it should work :/ It just crashes at this piece of code:

Private void UpdateGUI()
{
    string selectedItem  = cmbDisplayOptions.Items[cmbDisplayOptions.SelectedIndex].ToString();
    rdbtReserv.Checked = true;            
    lstReservations.Items.Clear();           
    lstReservations.Items.AddRange(m_seatMngr.GetSeatInfoStrings(selectedItem));
}

lstReservations.Items.AddRange(m_seatMngr.GetSeatInfoStrings(selectedItem)); Gives me the ArgumentNullExeption, but to me it should not do that.

the addrange sends string selectedItem to another class:

    public string[] GetSeatInfoStrings(string selectedItem)
    {
        int count = GetNumOfSeats(selectedItem);

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

        string[] strSeatInfoStrings = new string[count];

        for (int index = 0; index <= m_totNumOfSeats - 1; index++)
        {
            strSeatInfoStrings[index] = GetSeatInfoAt(index); 
        }

        return strSeatInfoStrings;

    }

This int count = GetNumOfSeats(selectedItem); goes to here and returns with an int:

    private int GetNumOfSeats(string selectedItem)
    {
        if (selectedItem == "ReservedSeats")
        {
            return GetNumReserved();
        }
        if (selectedItem == "VacantSeats")
        {
            return GetNumVacant();
        }
        else
        {
            return m_totNumOfSeats;
        }
    }

I have checked the arrayed have the correct number of spaces(60) and that selectedItem has a string(Allseats to start with so it should return m_totnumOfSeats which is an int of 60) But then in the private int GetNumOfSeats something goes wrong and it returns null and…well why?

I can’t see the problem.. maybe gone blind by trying to find the issue. Always got outstanding help here and I have learned tons!! So maybe someone can point out all the issues there is in my code.

Thanks a million in advance for any and all advice!

//Regards

Answer 1

Check if your variables are actually initialized and returns correct values.

There are logical errors in the GetSeatInfoStrings methods and the GetNumofSeats method.

Lucky for you the GetNumOfSeats method will always return 60 for you because of the wrong way you compare strings. It’s not the right way, so use the Equals method for comparison like

 if (selectedItem.Equals("ReservedSeats"))

With that you will get a proper output form GetNumOfSeats(string) method.

The next thing is to fix your looping in the GetSeatInfoStrings method so as to not get an array index out of bounds exception like this.

    string[] strSeatInfoStrings = new string[count];

    for (int index = 0; index <= count; index++)
    {
        strSeatInfoStrings[index] = GetSeatInfoAt(index); 
    }

    return strSeatInfoStrings;

Also fix the part where your logic returns a null in the GetSeatInfoStrings method. it should return an empty string array according to your logic as

    return new string[0];

That should probably get your methods working. You need to be very careful of what you code before you debug it 🙂