Actions Scrip 3.0 Else If Conditions (TEXT)

i need to make a Else If Conditions. I make a form with Adobe Flash, at the first page, i need to make a login form. I want to make Input Text, but the input text must be filled. If the input text is empty, i want to make alert if the form must be filled. In my idea. its have a one input text called "nama.text" and in the bottom of the input text, i put a button called "next.text". And then, i put dynamic text "alert.text" in the bottom of the button.

I want, if the button pressed by user with a filled input text, user will be direct to go to next frame. But, if the input text is empty, i want to make alert "Nama Must Be filled" and make user stay in this page and cannot go to next frame until the Nama.text is filled. Iam so sorry for my english, but i hope, everyone here understand with my questions. Big Thanks :)