I highly recommend you to look at popular open-source projects in your field even before you start developing something. Because almost everything you want to create is already created by the community with a very high quality. I understood this a year ago when I discovered Open source in iOS for myself and now I discovered it in Android. In this post I will give you a MUST look list of references and projects.
A list of important and popular open-source projects on GitHub for Android and iOS can be found here:
By best match:
By most stars:
By most forks: