How to use a library project with both c and java apis on Android

问题

I have asked this question in google android-ndk group but not get any answer.

I am trying to build a common module in a independent project by click the "Is Library" is eclipse. This project provides both c apis and java apis. While some of these apis are related. ( it means it's not a good idea to separate them into 2 projects) Let's name it common and libcommon.so.

When I am using this library in another project ( suppose testcommon), I add the common project as a library in eclipse at project explorer--> properties --> Android --> Library --> Add. But this only make me possible to use java apis in the library.

Also I add libcommon.so as a PREBUILT_SHARED_LIBRARY in android.mk in testcommon project so that I could access c apis. ( as below )

include $(CLEAR_VARS) 
LOCAL_MODULE := common-prebuilt 
LOCAL_SRC_FILES := ../../common/libs/$(TARGET_ARCH_ABI)/libcommon.so 
include $(PREBUILT_SHARED_LIBRARY) 

include $(CLEAR_VARS)
LOCAL_MODULE    := testCommon 
LOCAL_SRC_FILES := testCommon.c 
LOCAL_C_INCLUDES := $(LOCAL_PATH)/../../common/jni/include/ 
LOCAL_SHARED_LIBRARIES := common-prebuilt 
include $(BUILD_SHARED_LIBRARY)

In this way, ndk-build is success but when I am running it, I get below errors:

[2012-02-29 15:28:20 - testCommon] Error generating final archive: 
Found duplicate file for APK: lib/armeabi/libcommon.so 
Origin 1: E:\Code\EclipseWorkspace\testCommon\libs\armeabi\libcommon.so 
Origin 2: E:\Code\EclipseWorkspace\Common\libs\armeabi\libcommon.so

I think that because both reference to library and prebuild shared library add libcommon.so to testcommon project. In fact, I have tested to only reference the library or add a prebuild shared library, they both copied libcommon.so to testcommon.

The question is, what should I do if I need a library with both c and java apis.( not only code )

Thanks

After I read Can shared library call another shared library?, I found a way to solve this but still not very sure.

Use below line in Android.mk instead of PREBUILT_SHARED_LIBRARY also make native part works and libraries will not be copied in this way. So that duplicate copy could be fixed.

LOCAL_LDFLAGS := -L$(LOCAL_PATH)/../../Common/libs/$(TARGET_ARCH_ABI)/ -lcommon

The reason why this could not work in my before test is that even is this way, both libraries should be load in java, but not only libtestCommon.

System.loadLibrary("common"); // I lost this in my before test
System.loadLibrary("testCommon");

I think it's clear for me now.

Both LOCAL_SHARED_LIBRARIES and -L plus -l should work fine in NDK.

The problem is that when I call

System.loadLibrary("testCommon")

it will try to find so files at /data/data/$(app path)/lib (System.java::loadLibrary --> Runtime.java::loadLibrary --> DexPathList.java::findLibrary ) but when libtestCommon try to find its dependency libCommon.so, it will only find it at /vendor/lib and /system/lib since

LD_LIBRARY_PATH=/vendor/lib:/system/lib.

If I call System.loadLibrary("common") first, dlopen will load it into cache (Linker.c::alloc_info). This make libtestCommon.so loads libCommon.so success I guess. So everything works.

I also noticed these words at the end of SYSTEM-ISSUES.html in ndk-r7:

A bug prevents one application shared library from depending on another one. For example, if you build both libfoo.so and libbar.so for your application, and list libfoo.so as a dependency for libbar.so in bar/Android.mk (with LOCAL_SHARED_LIBRARIES := foo), then loading libbar.so will always fail, even if you have already loaded libfoo.so in your process.

There is a little different. If I have already loaded libfoo.so in my process, libbar.so will success.

So, answer at last is:

Use LOCAL_LDFLAGS := -Lxx -lxx if you need any shared libraries in android library project.
You must call System.loadLibrary for every shared libraries needed. That's also the way to use another shared library in one library.
The path of libraries at /libs/ is placed at /data/data//lib/.

回答1:

As an option you can use

LOCAL_ALLOW_UNDEFINED_SYMBOLS := true

in one of Android.mk and exclude the duplicate lib.

回答2:

I have been wrestling with a similar problem. I want to build an Android library project with both Java and C. I want dependent projects' Java to be able to reference the library's Java and dependent projects' C code in JNI to be able to reference the C in the library's jni. I required two kludges. One is almost identical to your solution:

LOCAL_LDFLAGS := -L$(LOCAL_PATH)/../../Common/libs/$(TARGET_ARCH_ABI)/ -lcommon

I created a dependency on the library project's actual location in the file system. Your dependency assumes the Common library project is a sibling directory of your dependent TestCommon project.

I also created a build.xml Ant file that copies the C header files from the library project to a jni/include directory in the dependent jni folder.

With these two kludges, I am able to get everything working. I would really like to eliminate both kludges, but could not find a way.

来源：https://stackoverflow.com/questions/9510162/how-to-use-a-library-project-with-both-c-and-java-apis-on-android

标签

android

android-ndk

android-library