Installing & using the Android NDK in Eclipse

As simply as I can describe it, building an Android app from within Eclipse that uses the NDK requires two steps.

First, inside your terminal you need to run the NDK build script on your project. cd into the root of your project directory and then execute the ndk-build script within that directory.

For example:

cd ~/workspace/hello-jni
./~/android-ndk-1.5_r1/ndk-build

After doing this, you should see some output that results in the creation of a *.SO file within the obj directory within your project directory.

Once you have the *.SO file, the final step to building an application with the Android NDK through Eclipse is to build it with Eclipse like you would any other application and then deploy it for testing.

If you make any changes to the C/C++ code you'll need to repeat step one and regenerate your *.SO file before building and deploying your application from within Eclipse again.

I would like to note that by using the Android NDK your android apps are still based upon Java. They're just communicating with code written in C/C++ by way of the Java Native Interface.

Finally, I am not aware of any Eclipse plugins that will aid with NDK development. Everything I know about the NDK I have learned the official Android NDK documentation. Please feel free to comment and let me know if there anything I can clear up in my response.

The docs directory in the NDK has some pretty good information on how to use the NDK itself. Read the overview, Application.mk, and Android.mk HTML docs. You'll want to google for the Sun JNI PDF, download it, and learn what JNI is all about before you go any further. This is because simply compiling a bunch of C/C++ code into libraries with the NDK is only part of the process. You have to write native Java code that calls your C/C++, and you have to create wrapper functions in C/C++ that adhere to JNI conventions that the native Java code can invoke. JNI has been around a long time, it's not Android specific by any means. So, you can, to learn about it, go quite far following tutorials geared towards JNI, using command line tools like javah and javac, and then return to integrating with the NDK after you know the basics. (For an example of what these C shims look like, take a look at the hello-jni sample in the NDK; the C source file there shows you typically what the shims look like. Using javah to generate these shims is the way to go, you create Java classes that have native methods, process them with javah, and it generates the C headers for you, then you code up C functions that adhere to the generated function prototypes).

Note: while the NDK docs would have you manually building from command line and then going into Eclipse to build your app (a laborious sequence of steps, to be sure, especially if you are changing the C/C++ code), it turns out you can integrate easily with Eclipse so that the NDK is run each time you build from Eclipse. To see how, read here.