Visual Basic.NET - aceptar solo números en la columna cantidad del datagridview

Private Sub DataGridView1_EditingControlShowing(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles DataGridView1.EditingControlShowing

        Try

            RemoveHandler e.Control.KeyPress, AddressOf typeOnlynumbers

            AddHandler e.Control.KeyPress, AddressOf typeOnlynumbers

        Catch ex As Exception

            MessageBox.Show("Error something went wrong!!")

        End Try

    End Sub

    Sub typeOnlynumbers(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs)

        If Asc(e.KeyChar) >= 33 And Asc(e.KeyChar) <= 47 Or _

            Asc(e.KeyChar) >= 58 Then

            e.Handled = True

        End If

    End Sub

dim fila as integer= dgv.count -1

dim item as integer = 0 'aquí va el indice de la columna que quieres consultar, adaptala a tu proyecto

if dgv.rows(fila).cells.item(item).value.tostring = nothing then

   msgbox("rellene el campo x")

   exit sub

else

'lo que deseas hacer, sino le quitas el else

end if