Most design folks get this wrong. Visual Design is what triggers the impulse of the mobile user to download a mobile app to try it.
OOP Dev Best Practices is what takes the feature set of the android application and allows the developer to make a set of architecture choices that make a intensively highly stable app which than moves the monthly user retention curve for that android application upward. As choosing the right Architecture choices gives the developer a flexible framework to evolve the app-user-work-flow to impact and move the monthly user retention curve upward.
If you do not start with a strong android java developer you will not get that highly stable android app container to inject the visual design into for that first impulse download or buy. Thus, you will get instead a high initial download rate but somewhat poor user retention curves.
I have to state it this way due to past experience at a Music Start-Up last year. In that they used an outside firm to tell them that social media impacts the user-retention-curve, well not it does not impact the user-retention-curve but instead like visual design impacts the first user impulse to download that app and try that app.
The reason why this is important is that start-ups only get funding past speculation when the user-retention-curve data indicates a sticky product as far as high monthly amounts of users using the mobile app.