Object reference not set to an instance of an object.

Nel

Hi,

I want to check the value of the combobox in one form from another.
I have this code in button2_Click event

            Blagajna bl = (Blagajna)Application.OpenForms["Blagajna"];
            ComboBox cb = (ComboBox)bl.Controls["comboBoxVal"];
            String kom = (cb.SelectedItem).ToString();

and
Blagajna bl = new Blagajna();
in partial class definition.

I get this errorr: "Object reference not set to an instance of an object."

Could anybody help me please what is the problem with the code?

Thanks in advance.

7 Replies

Know the answer? Post it — somebody with the same question will find it here.

Nel14y ago
Thanks Vulpes
0
Vulpes14y ago
First of all, you don't need this line which is creating a new instance of Blagajna rather than obtaining a reference to the existing instance:

Blagajna bl = new Blagajna();

Secondly, the most likely reason why you're getting the null reference exception is because the combobox has not been placed directly on the form but within some container such as a panel or a groupbox.

If it has been placed on a panel (panel1 say), then you can still 'drill down' to it as follows:

Blagajna bl = (Blagajna)Application.OpenForms["Blagajna"];
Panel pl = (Panel)bl.Controls["panel1"];
ComboBox cb = (ComboBox)pl.Controls["comboBoxVal"]; // now accessing panel's Controls collection
String kom = cb.SelectedItem.ToString();

There's also an easier way to do it which is to change the combobox's default Modifiers property from private to internal. You can then simply do:

Blagajna bl = (Blagajna)Application.OpenForms["Blagajna"];
ComboBox cb = bl.comboBoxVal; // now can access combobox directly as it's internal
String kom = cb.SelectedItem.ToString();

0
Jignesh Trivedi14y ago
hi Nel,

I thing your cb.SelectedItem property is null and you call is override method .Tostring()

try..
String kom = Convert.ToString(cb.SelectedItem);

But find out why SelectedItem is null.

hope this will help.
0
Nel14y ago
I have Blagajna bl = new Blagajna();
FOR AN INSTANCE OF Blagajna.

I debug the line and get null for kom, but I don't understand why, when the combo in the form Blagajna which I call in the second form has value "EUR" or some other but not null:(
0
S G14y ago
Hi,
This error is occur because u forget to make the instane of object. When we create an object we use the keyword "new" . So in u r program i dont know on which line u get an error . But trace the line of the error and give its instance. Currently it can get a null reference. There is chances that the error at combobox. Do this . I will help you exactly.
0
Nel14y ago
The combobox does have a value which is not null in the form I call from this form.

I get the error in this line:

String kom = (cb.SelectedItem).ToString();
0
Jignesh Trivedi14y ago
hi,

this type of error come when you access property of null object or casting null to other object.

can you please share which line you got error.

thx.
0