add a new element that depend to selected item of combobox

Question

 i have a issue when i want to add a new row in my table


When i don't fill all of the components, the event didn't work


i think that the issue came from the combobox because when i do the same thing with TextBox it work 


 table ab = new table();

ab.IDTable = int.Parse(IDtextBox.Text);


tableB iss = (tableB)comboBox1.SelectedItem;

ab.name= (string)iss.name;
domaincontext.table.Add(ab);