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androidc++android-studiogradlendk-build

skip prebuilt-library.mk on gradle sync android studio

My project app depends on a library module alib. both app and alib build a c++ library with ndk. the app c++ lib, called app.so, depends on alib.so, which is the c++ lib for the library module. Inside the android.mk of app, i have:

LOCAL_PATH := $(the_right_alib_path)
include $(CLEAR_VARS)

LOCAL_MODULE := alibsdk
LOCAL_SRC_FILES := libalib.so
include $(PREBUILT_SHARED_LIBRARY)

Gradle sync fails on prebuilt-library.mk, with message Android NDK: Check that /the_right_alib_path/libalib.so exists or that its path is correct.

the file would be there if i build the module with gradle, it's naturally not there when I do gradle sync.

How can I skip the execution of prebuilt-library.mk? Alternatively there is a way to tell ndk that the alib.so will be built by another gradle module?

Ps. This is more annoying cause in reality it checks all the libraries for different versions/flavor/dimensions, and i don't need to build all those libraries to work on the dev version on the app.

Solution

  • You can avoid the error by small modification of the Android.mk:

    include $(CLEAR_VARS) 
LOCAL_MODULE := alibsdk
LOCAL_SRC_FILES := libalib.so
ifeq ($(findstring n,$(MAKEFLAGS)),n)
  include $(BUILD_SHARED_LIBRARY)
else
  include $(PREBUILT_SHARED_LIBRARY)
endif

    This takes advantage of the -n flag that is passed to ndk-build during sync. You can create a custom define for that, if you wish. build-shared-library.mk will generate a warning about strange SRC, but won't fail.

    Same can be achieved without touching the Android.mk files: in your build.gradle, use

    if (project.gradle.startParameter.taskNames.isEmpty()
 || project.gradle.startParameter.taskNames[0].contains(":generate")) {
  android.defaultConfig.externalNativeBuild.ndkBuild.arguments += 'PREBUILT_SHARED_LIBRARY=$(BUILD_SHARED_LIBRARY)'
}

    Android Studio runs ndk-build many times: with no tasks (the Sync step), within a :generate[flavor][Debug|Release]Sources, and within :externalNativeBuild[flavor][Debug|Release].

    To retrieve the current task, I followed https://stackoverflow.com/a/21603707/192373.

    Maybe the easiest fix is to rely on an obscure implementation detail of prebuilt-library.mk*). Early in your main Android.mk, add the line

    override prebuilt=$(if $(strip $(wildcard $(prebuilt_path))),$(prebuilt_path),.)

    This can be done in gradle, if necessary:

    android.defaultConfig.externalNativeBuild.ndkBuild {
   arguments 'prebuilt=$(if $(strip $(wildcard $(prebuilt_path))),$(prebuilt_path),.)'
}

    *) verified for NDK r19b and earlier.