Masking Effect with Gradient

I've tried for several times, thinking on how to make a gradient fade on my masking layer but it was hard and I couldn't find a solution for it. This is some outcome that I've tried.

At first, I've tried pulling gradient from photoshop and illustration but it wouldn't work. But I do not know how to place gradient in flash so I search for tutorial and I found this which teach me. 

This tutorial teaches on how to use gradient in Flash and it helps too. So I tried doing it in flash.

But it failed. As you can see, although I placed it as an gradient, it still changes into a solid circle after masking. It was really frustrating because I thought it will be fine and easy to get the technique but it wasn't. So I ask one of my past lecture who teaches me animation. He told me I couldn't do it using just masking. So he gave me one sample which using codes. And it was what I wanted!!! I was so thankful.

This was his file, 3 simple line of masking using codes. It thought me on how the codes work for masking gradient fade masking on Adobe flash. So I implement it to my project and it works perfectly. 

Referencing

Youtube (2013) Adobe Flash CS5 - Gradient Tutorial. [video online] Available at: http://www.youtube.com/watch?v=pJfbRfps-xM&feature=player_embedded [Accessed: 21 January 2013].

JiaWern, K. (2013) Masking Coding Effect. [Lecture]