Question null reference exception unhandled problem

[Spartacus]

dear
i am beginner in ADO.net and this is my first program and i have some problems my data base as in picture

so i need help to solve it ,, the problem is

null reference exception unhandled
as in picture below

s



please any one have an idea how to solve this problem

 

[Don Delegate]

Combobox2.SelectedValue is Nothing.
Use

TextBox4.Text = String.Format("{0}", Combobox2.SelectedValue)

or test for Nothing

If Combobox2.SelectedValue IsNot Nothing Then
    TextBox4.Text = Combobox2.SelectedValue.ToString
Else
    TextBox4.Clear
End If

Also: do yourself a favour and give your controls a more meaningful name.

 

[Spartacus]

thank you very much it is now working