Call KeyPress Event in TextChange Event

private void txtCategoryCode_TextChanged(object sender, EventArgs e)
        {
            
            txtCategoryCode.KeyPress += new KeyPressEventHandler(MyKeyPress);
        }

        void MyKeyPress(object sender, KeyPressEventArgs e)
        {
            TextBox txt = sender as TextBox;
            if (txt.Text.Length > 3)
            {
                e.Handled = true;
                MessageBox.Show("Category Code should be in 3 letters.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }