invalidate() inside of a thread android app

I'm new to programming androids but I have quite a bit of experience programming blackberries.

I created an app that has an activity class (main.java) and a view class (game.java).

Inside the view class I have some bitmaps being drawn to the screen. I created a thread and I'm moving the images around in the thread. However when I call invalidate() inside the thread it never redraws the screen.

Are you not able to invalidate() the screen from a thread? I know the thread is running and the invalidate is being called, it just never makes the changes on the screen.