Panel Issue

Question

Hi all i am having a Panel control on my form and i copied some controls from another form and placed inside the panel. I have given some error provider for some controls but those did not fire until i hit save button. I Have written a validation as

  private void txtImmediateddest_Validating(object sender, CancelEventArgs e)
        {
            if (txtImmediateddest.Text == string.Empty)
            {
                TestClass test = new TestClass();
                test.RequiredText(txtImmediateddest, toolTipimmeddest);
            }
            else
            {
                TestLength tstlen = new TestLength();
                tstlen.ReqLength(txtImmediateddest, toolTipimmeddest);
            }

        }

But this does not work while leaving that particular text box can any one tell how to validate that