Step By Step Tutorial to Android NDK in Linux Environment

Before we begin coding and setting up the environments, I will give some basic introduction to terminologies we will use here.

Q1. What is Android NDK?

Ans.  Android native development kit is a set set of tools  that helps in implementing native code from languages like C and C++. You should only use NDK if it is really required in your apps, never use NDK if you just prefer programming in C or C++. Doing so will result in complexity.

Q2. Where to use NDK?

Ans. NDK should be used where intensive CPU uses is required in your application, such as physics simulation, signal processing, etc.

Getting Started:

Before we start we will need to download and install a couple of things:-

Eclipse with Android SDK

The SDK comes with pre bundled eclipse and is located at http://developer.android.com/sdk/index.html. Extarct this bundle in your home/root directory. Click the eclipse icon and start developing, thats it.

Android NDK Setup

The NDK can be downloded  from http://developer.android.com/tools/sdk/ndk/index.html. Extarct this bundle in your home/root directory.

Now goto back to Eclipse environment.

Click on window->prefrences->android->NDK.

Choose the extracted NDK folder.

Getting started with project development:

Step 1:

Create a new android project in using that extracted SDK Bundle, for this example I will call it NdkTrial.

Step 2:

Create a new folder called 'jni'(small letters, no quotes) in the root directory of your project.

Step 3:

The next thing we need to do is to setup Eclipse so we can build the JNI code. Click on Run->External 

Tools-> and choose the 'External Tools Configuration...'

Mark the 'Program' and click on the 'new'-icon.

Give it a Name(Can be any name)

Click on Main Tab.

Location is the location of the external tool you want to run, in our case the ndk-build file.

Click on 'Browse file system...' and locate the ndk-build file located under your NDK folder.

Refresh Tab Settings should be like this:

Build Tab Settings should be like this:

Now Click Run and you will get an error *** Android NDK: Aborting...

If you get this error then your setup to the ndk-build works and you are missing the Android.mk file.

STEP 4:

Create a new file called Android.mk in the jni folder.

In the Android.mk file write :

    LOCAL_PATH := $(call my-dir)

    

    include $(CLEAR_VARS)

    

    LOCAL_LDLIBS := -llog

    

    LOCAL_MODULE := xyz

    LOCAL_SRC_FILES := native.c

    

    include $(BUILD_SHARED_LIBRARY)

STEP 5:

Create a native.c file in jni folder.

In the native.c file write this:

#include <jni.h>

#include <string.h>

//Prefix Java, package name , class name with c function.  Change the dots to underscore

jstring Java_com_nexg_ndktrial_NDKActivity_display(JNIEnv* env, jobject thiz) {

            return (*env)->NewStringUTF(env, "Sanidhya09 Says: Hello from C");

}

STEP  6:

Now go back to external tools and click run again.

It will generate .so files in libs directory.

Now you should get successfull build.

STEP  7:

Now modify for Activity Class with this code:

public class NDKActivity extends Activity {

      @Override

      protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);

              TextView  tv = new TextView(this);

              tv.setText( display() );

              setContentView(tv);

            

             // Toast.makeText(this, ""+display2(),                                 Toast.LENGTH_SHORT).show();

          }

          public native String  display();

          /* this is used to load the “.so” library on application

           * startup. The library has already been unpacked into

           * /data/data/com.nexg.NdkTrial/obj/libxyz.so at

           * installation time by the package manager.

           */

          static {

              System.loadLibrary("xyz");

          }

     

}

STEP 7:

Test the program in device or Emulator.

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Thank You