NullReferenceException when i try to choose in combobox

Question

I'm beginner and I have small problem. I need check if it is not empty die combobox. Now when I click button and the Combobox give an null error

"An unhandled exception of type 'System.NullReferenceException' occurred in WindowsFormsApplication4.exe

Additional information: Object reference not set to an instance of an object.

 private void Wykonaj_Click(object sender, EventArgs e)
        {           

        if (Combobox1.SelectedIndex.ToString() != null)
        {
            if (Combobox.SelectedItem.ToString() != "Audi")
            {
                wersja= "110";
            }
            else
            {
                wersja = "101";
            }
        }
    }

Where is `wersja` declared? – garfbradaz Dec 20 '16 at 14:05 — garfbradaz, Dec 20 '16 at 14:05

score 1 · Answer 1 · answered Dec 20 '16 at 14:05

1

You have mistake in typing. Replace

if (Combobox.SelectedItem.ToString() != "Audi")

with

if (Combobox1.SelectedItem.ToString() != "Audi")

answered Dec 20 '16 at 14:05

Nenad J.

331
2
8

LOL ... then that would cause a compiler error instead of a runtime exception – Rahul Dec 20 '16 at 14:06

score 1 · Answer 2 · answered Dec 20 '16 at 14:11

1

string wersja = string.Empty;
if(Combobox.SelectedIndex > 0)
{
    if (Combobox.SelectedItem.ToString() != "Audi")
    {
        wersja= "110";
    }
    else
    {
        wersja = "101";
    }
}

answered Dec 20 '16 at 14:11

Joris van Roy

183
1
1
12

While this code snippet may solve the question, [including an explanation](//meta.stackexchange.com/questions/114762/explaining-entirely-code-based-answers) really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion. Please also try not to crowd your code with explanatory comments, this reduces the readability of both the code and the explanations! – kayess Dec 20 '16 at 14:40

score 1 · Accepted Answer · edited Dec 21 '16 at 02:13

1

In your case either Combobox.SelectedItem or Combobox1.SelectedItem is null If they are different comboboxes. In c# null.ToString() throws NullReferenceException which means if that value is null means definitely exception will thrown. I would like to suggest you to use like this:

if (Combobox1.SelectedIndex >= 0)
{
    if (Combobox.SelectedItem != null && Combobox.SelectedItem.ToString() != "Audi")
       wersja = "110";
    else
       wersja = "101";
}

Here you are checking for null and if it is not null then check its value with "Audi"

edited Dec 21 '16 at 02:13

Rob

26,989
16
82
98

answered Dec 20 '16 at 14:13

sujith karivelil

28,671
6
55
88

Thanks you !! The solution was "if (Combobox.SelectedIndex >= 0)" – Mariusz Nazwiskoo Dec 20 '16 at 18:32
@un-lucky You've been here long enough to know this question has been duplicated *many* times before. Please flag such questions as duplicates rather than providing tailored answers to each. Thanks! – Rob Dec 21 '16 at 01:58
1

I was not the First one to answer this question, When I saw the questions 2 answers ware already posted here and are confusing and not clear enough, That's why I have answered, forgive me if it is wrong, anyway Thanks for your comment @Rob – sujith karivelil Dec 21 '16 at 02:11

NullReferenceException when i try to choose in combobox

3 Answers3