Where can I find some good examples of Android UI? [closed]

I'm quite new to the Android world, and, due to work needs, I'm trying to get in. Whilst I'm not particularly afraid of the "thinking" code (i.e. Java), I'm a bit confused when developing the user interface.

Since I found that the simplest yet most effective way to learn something is copying from those who are the best, I'm wondering if there's some resource or something, out there, well done.

I mean: do you know some open source app, from which I can build my own knowledge about Android layouts? I wasn't able to do it on my own, even though I wondered quite a lot!

What is an Android UI?

The user interface (UI) for an Android app is built as a hierarchy of layouts and widgets. The layouts are ViewGroup objects, containers that control how their child views are positioned on the screen. Widgets are View objects, UI components such as buttons and text boxes.

1) A good summary on everything UI design in Android can be found here.

2) The best place to get started is directly from the official website.

And here are relevant examples that are considered as good design in Android.