how to check that all columns are filled

Hi, i think a better apporch is to check that the user have filled the data correctly in the begining.

To check if the datagridview contains valid data you may use somthing like this:

foreach (DataGridViewRow row in dataGridView1.Rows)
                {
                    if (row.Cells[1].Value.toString()) == "") //depends on your not filled cell                                                           //logic 
                    {

//the cell is empty, you may in your case check if the value is null
                        
                    }
                }

I am totaly against using this kind of solution. the best way is to create a class and then affect the class to the datagrid.
your will then work only with lists. much easier, faster and efficient.

//you will have to iterate throw the elements of your list.
Foreach(User user in userList)
{
if(user.Name == null || user.Name == "")
   {
      //the user Name is not filled
   }
}

Hope you will consider using the second solution.

Hope it helps.