Android regenerate optimised dex file

Question

I'm trying to understand a few things around how dex files are handled by android.

What I do know is that an APK ships a dex file, the system gets it, optimises it at install time, and stores the resulting ODEX file (optimised dex) at /data/dalvik-cache/myOdexfile and then runs the application from there.

Is that really how it works?

What happens when a dex file downloads and opens a new dex file from the internet? is that optimised as well?

Also - the system, afaik, keeps the original APK around, right? I think that is kept at /data/app/myAPK-1.apk. Is that used in any way by the system? When?

Can you somehow manually force regeneration of the odex file from the stored APK file after installation?

Answer 1

Yes, Android creates ODEXs from DEXs at install-time.

Yes, the APK is saved. DEX and ODEX only contain code. The APK is where all your resources and assets come from - your label, your icon, your layouts, etc.

To my understanding DEX optimization is purely an install-time process, and is not performed on any DEX that is not part of an installed APK. And since a DEX that is part of an APK cannot change without installing a new APK, there is no need to regenerate an ODEX outside of the normal install process.

Answer 2

When you load a dex file dynamically, dalvik will optimize it the first time it is loaded. You have to pass a directory that you application can write to, for it to place the cached odex in, typically within the application's data dir.