Develop Reference

How to call a Android ndk build .so file in another Android application?

I have an requirement which i have to build .so file using NDK build in Android and I have to call some of the methods from the .so file in my other Android application.
What I have tried so far.
I have taken the .so file from the lib folder of my Android project and put in my other application libs folder where I should call that .so file. I have used the below code:
Note: I am using ECLIPSE
static {
System.loadLibrary("NativeCode");
}
and also tried with full path of library
static {
System.loadLibrary("fullpath\NativeCode");
}
both the cases its giving unsatisfiedLinkError that mean it's not getting the path of my .so file.

You need to have your libNativeCode.so in the jni folder of your root, and not in the libs or lib folder
Here is a nice tutorial : http://www3.ntu.edu.sg/home/ehchua/programming/android/android_ndk.html
Alternatively, you can use following commands:
adb shell
$echo $PATH
What it will do is display a path like this :
/sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin
You can have your .so in any of these folders like /system, /system/bin, /system/sbin. (Remember, but you would need to manually copy it, and it is not a good idea to do so for an app)
Edit :
You can not call any JNI function in your app, because the signature. You need to have a JNI wrapper (a .so JNI lib that in turn uses the .h header file to call the JNI function of the other library). This is because JNI is very sensitive to signatures. So, as I recommended earlier, follow the tutorial !

In order to get your .so library to be loaded using loadLibrary() you'll have to copy the libNativeCode.so lib into the jniLibs/architecture folder.
The folder should be located under src/main/jniLibs/armeabi-v7a of your Android Application module (assuming you're using Android Studio).
After you copy the libraries, add the following line to your build.gradle located at the app module folder:
assert file("./src/main/jniLibs/armeabi-v7a/libNativeCode.so").exists()
After you'll complete the above steps it should load the lib properly.
If the libNativeCode.so is located at the wrong path, the Gradle build will fail.
Good luck,

How can we know which .so file a particular cpp file is in? (in Android rom)

I found some modified code in a cpp file in android to protect smartphone from stagefright vulnerability.
I want to change it with original cpp file and rebuild to a new android ROM file.
The problem is,
I downloaded an android factory image from google developer forum and
I unpacked it with android kitchen tool.
Now I can see its contents but I couldnt find the file, I wanted to modify, "/media/libstagefright/MPEGExtractor.cpp".
There are only some .so files in system/lib/ folders.
I heard it's almost impossible to decompile those .so files.
I tried googling to find out which .so files have "MPEGExtractor.cpp", so that I would be able to compile some files including that cpp file into a .so file, and change it, and rebuild it a new ROM.. but I couldn't find out.
What should I do to rebuild it with some code to be changed?
Thank you for reading

SO(Shared Object) are files that are compiled from source. By definition they do not contain the symbol information you are asking for.

Add .so file to android solution

I don't know how to use .so files in my project. So I downloaded the ffmpeg.so file and now I need to add it to my solution so that I can convert video formats on my device but I do not know how. I tried finding tutorials on the internet on how to add this file but nothing seems to work for me.
Do I still need the Android NDK to compile my C code as I have the .so file.
Any good tutorials how I can add this library to my solution?

Put the file named libffmpeg.so into libs/armeabi subdirectory of your project. You don't need NDK if you don't have C/C++ sources of your own.
A mistake that happen sometimes is that the Android name expectations are not met. The name must start with lib and end with .so.

Questions on how the build .c files

I have been trying to implement the API for the serial port found the the below web page. I am a beginner in all this and I am sure about what I am looking at:
http://code.google.com/p/android-serialport-api/source/browse/#svn%2Ftrunk%2Fandroid-serialport-api%2Fproject%2Fjni
Questions:
1) The .c files are built how? Do I need to download the NDK? I assume the .c file is run directly by the virtual machine, or what? Or is the executable for the .c the file in the libs directory? If so, how do I utilize the libserial_por.so file?
Thanks!

The .c files are built into a library by running ndk-build in the project directory. You need the NDK.
The .c files are not run directly by the virtual machine, but rather a library is created in the libs directory, which is then loaded along with the SerialPort class.
To use the library, just use the SerialPort class which already has bindings to the library.
C files will be compiled to an ARM binary library with the extension .so by the NDK. Take a look at the NDK Documentation, section "Getting Started with the NDK", to find out how to use it.
Basically, you place your .c files in the jni directory, change Android.mk to specify how to compile them, then run ndk-build to build the library. The resulting lib<name>.so will be placed in the lib directory. You then use your library in the Java project with System.loadLibrary('<name>').
This of course means the library must have a JNI interface for you to be able to use with the Java application, since Android doesn't support JNA yet.
I see though that the code you pointed out is an Android project. To run it, simply run ndk-build in the project directory to build the library, then run the project in an emulator.

Creating a product SDK: How do I add a native lib (.so) and a jar with the SDK I am creating?

I am creating a widget that we will provide to developer end users and it consists of a .jar and a native library (.so) built using the NDK. The JAR has a JNI interface to the dynamic library.
It's very clear on how to include an external .jar in a project but not how to include a dependent dynamic library.
How do I package up and build the .jar and .so? What are the best practices here?
I can create the JAR file using the JDK's jar command. Do I need to run dx.bat on the jar to convert to Dalvik bytecode?
I need to create a sample project showing the widget in action. How do I include this .jar and .so in a sample project that demonstrates how to use the widget?

I spent some time on this, and i just can't understand why isn't this written on wikitude documentation.... anyway follow this changes!
go to windows/preferences/android/build
uncheck the first and the second option
extract files from wikitudesdk.jar with winrar as if it is an archive, search libarchitect.so and copy it in /libs/libs/armeabi/
add wikitudesdk.jar to your build path

You should use the standard build tools included with the SDK for this. If you include the .jar files you need in the /lib directory of your project, the ant build process will convert the included class files to Dalvik bytecode format and include them in your classes.dex file for the app. Add a build.properties file to your project root as well, with one line:
external.libs.dir=lib
Depending on the version of your SDK and configuration of it, you may need to place the jar in libs rather than lib.
As for the .so, I presume that it's properly compiled using the Android NDK, or using a build script that uses the proper compiler and compiler flags that are required to successfully link the shared object on Android. If this is the case, you can include the .so file in libs/armeabi and they will be added in the jar as well. Furthermore, the dynamic library loader will know to look in this location in the .jar when you actually try to load the library from Java code.

Using ADT 12, I accomplished this by doing the following:
1) Export JAR from your library with the SO file using Eclipse. Make sure you exclude AndroidManifest.xml. This will include source code and other data, so if you are distributing, you'll want to strip these unnecessary bits out using any ZIP utility.
2) Create a directory in your App's source tree (I use "lib" directory) and copy your library JAR to it.
3) Right-click project in Eclipse and select "Configure Build Path". Add JAR and point it to JAR inside your App source tree.
4) In your Eclipse preferences, select Android/Build section and uncheck "Automatically refresh Resources and Assets folder on build". You will notice an option below that says "Force error when external jars contain native libraries." There is an ADT bug, which will supposedly be fixed in R17, which uses the wrong setting. Once it is fixed, you will use the "Force error" one (make sure it unchecked).
5) Once you build your app APK, you will have a libs/armeabi/libXXXX.so file. This will not be automatically unpacked on install. You will need to write code to extract it from your APK file into your data directory, then use System.load on the .so file in your data directory.
I have bidirectional JNI calls going from the dynamically loaded file, and even use dlopen() on it to do my custom plugin registration stuff.

Add the below lines to android.mk.
include $(BUILD_PACKAGE)
LOCAL_PREBUILT_STATIC_JAVA_LIBRARIES := alias:libs/your.jar
include $(BUILD_MULTI_PREBUILT)