How to avoid reverse engineering of an APK file?

Question

I am developing a payment processing app for Android, and I want to prevent a hacker from accessing any resources, assets or source code from the APK file.<

Answer 1

At no point in the history of computing has it ever been possible to prevent reverse-engineering of software when you give a working copy of it to your attacker. Also, in most likelihood, it never will be possible.

With that understood, there is an obvious solution: don't give your secrets to your attacker. While you can't protect the contents of your APK, what you can protect is anything you don't distribute. Typically this is server-side software used for things like activation, payments, rule-enforcement, and other juicy bits of code. You can protect valuable assets by not distributing them in your APK. Instead, set up a server that responds to requests from your app, "uses" the assets (whatever that might mean) and then sends the result back to the app. If this model doesn't work for the assets you have in mind, then you may want to re-think your strategy.

Also, if your primary goal is to prevent app piracy: don't even bother. You've already burned more time and money on this problem than any anti-piracy measure could possibly ever hope to save you. The return on investment for solving this problem is so low that it doesn't make sense to even think about it.