Question

I have a rather large Android project, and it takes considerable amounts of time for the sdk to do the resource-parsing / dexing / etc. I’d like to improve this somehow.

I’ve read that Android library projects can contain resources now too. So we can also put Activities, Fragments, etc. in them.

Does this mean, that if I export parts of my large project into library projects which I reference from the main project, then I don’t have to rebuild the already built (and not modified) libraries again, when I rebuild the main project? So I only have to do the resource-parsing / dexing / etc. for the modified libraries and possibly the main project, decreasing the overall build time in most cases.

Answer 1

Does this mean, that if I export parts of my large project into library projects which I reference from the main project, then I don’t have to rebuild the already built (and not modified) libraries again, when I rebuild the main project?

Partially no, Android Library Project is not built directly, it is always built along with the dependent Main Project, when SDK compile/build the Main Project, SDK tools compile the Library Project into a temporary JAR file and uses it in the main project. whenever you re-build your Main Project, the referenced Library Project is re-built as a part of main project build life cycle, even though nothing changed in Library Project. Check out timestamp of the temporary JAR generated under your app-lib/bin folder for evidence, it always get changed every time yo build Main Project.

Quoting from official dev guide:

However, a library project differs from an standard Android application project in that you cannot compile it directly to its own .apk and run it on an Android device. Similarly, you cannot export the library project to a self-contained JAR file, as you would do for a true library. Instead, you must compile the library indirectly, by referencing the library in the dependent application and building that application.

When you build an application that depends on a library project, the SDK tools compile the library into a temporary JAR file and uses it in the main project, then uses the result to generate the .apk. In cases where a resource ID is defined in both the application and the library, the tools ensure that the resource declared in the application gets priority and that the resource in the library project is not compiled into the application .apk. This gives your application the flexibility to either use or redefine any resource behaviors or values that are defined in any library.

Android Library Project is different from regular java library project. where you can compile and build everything into and jar library once, and start import/use the class from reference jar dependencies in main project. Currently Android Library Project is designed on source-based mechanism, not compiled-code based library mechanism, as mentioned in this Android blog, although self-contained jar distribution is promised in future release (unfortunately not in neither r15, r16, r17 nor r18 yet).