After form loads assigned values to textbox

Hi experts,

I am developing through SAP B1 studio for Microsoft visual studio.  Usually, in the menu event/form load, we show the docnum,docdate fields values.Trying to assign values to textbox after form opens.So, in Form_LoadAfter, I am trying.But, this event calls even before form is shown. i.e,it is called immediately after clicking Menu to open the form.So, assigning values to textbox is showing error.Any inputs regarding this will be helpful...

Thanks in Advance,

Parvatha Solai.N