How to develop a android unlock screen app

I am student and I want to develop a android unlock screen app. I want to know what android api can give me some 开发者_开发百科helps and how can I set my app as the default unlock screen app. Thank you.

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This is not supported by the Android SDK today, sorry.

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I know this question is old. But just to help anyone seeing this post aand getting disheartened, I've found an answer on a comparable question on stackoverflow link, it might help now. There is also a new feature named DayDream in the API 4.2 this could be also interesting. It's a feature.

Hope it helps someone. Cheers :)