Source code of widgets

How do you view the source code of widgets? I'm trying to make a custom spinner by extending Spinner and am curious to see the orig开发者_如何学Goinal code.

In Eclipse, I've looked in Android 2.2 > android.jar > android.widget > Spinner.class but it tells me source not found.

Old question about spinners. (shows code) How can I extend spinner to implement a new function?

I would imagine that you only have to extend the class, define a custom layout and have it do what you want your spinner to do.