Object reference not set to an instance of an object.

Question

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.

Nel · Answer

Thanks Vulpes

Vulpes · Answer

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();

Jignesh Trivedi · Answer

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.

Nel · Answer

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:(

S G · Answer

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.

Nel · Answer

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();

Jignesh Trivedi · Answer

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.