Validating Datagridview in a form.

Question

i have a form, with datagrid where inputs are collected, together with a submission button. at the submission of this data, i want to validate the datagrid to check for empty cells.

from my code, the datagrid wont be validated until i have exited then it keeps bugging me with the messagebox message.

 

here is my code:

 

private void button3_Click(object sender, EventArgs e)
       {
           foreach (DataGridViewRow rw in this.dataGridView1.Rows)
           {
               for (int i = 0; i < rw.Cells.Count; i++)
               {
                   if (rw.Cells[i].Value == null || rw.Cells[i].Value == DBNull.Value || String.IsNullOrWhiteSpace(rw.Cells[i].Value.ToString()))
                   {
                       string message = "Sorry, But some Fields are Empty, Therefore, you cannot Proceed";
                       string caption = "Error Detected in Input";
                       MessageBoxButtons buttons = MessageBoxButtons.OK;
                       DialogResult result;

                       // Displays the MessageBox.

                       result = MessageBox.Show(message, caption, buttons);

                       if (result == System.Windows.Forms.DialogResult.OK)
                       {
                           return;
                       }
                   }
                   else
                   {
                       resultVV f3 = new resultVV();
                       f3.ShowDialog();
                       this.Hide();
                   }
               }
           }
       }