Android NDK JNI Windows xp/7 with 32/64 bit Installation Problems with Solutions in Eclipse without C/C++ CDT Plugin

Hi all,

I spent 2 days on configuring this. I read lot of blogs and instrutction steps from various sites. I would like share my experience on installing Android NDK and Working with Eclipse.

Objective:
Using JNI Technology in Eclipse with Android NDK r6/r7 on Windows xp/7 Professional

Pre-requirements:

1. Java SE SDK -- Java Development Kit
2. Eclipse Helios/Indigo -- IDE to work with Java, Android, C/C++ etc.
3. Android SDK -- Android Applications Development Kit
4. Android ADT Plugin for Eclipse -- Download the latest Android SDK Platform Tools
5. C/C++ Plugin for Eclipse (Optional) -- Make sure that .c, .cpp, .h files opening from Eclipse
6. Android NDK (r6/r7) -- Native development i.e. Running c libraries in Android
7. Cygwin 1.7.x or above -- Makefile creation, Library file creation tools, Compiling C files

Installation:

1. Install the Java Development Kit
   
2. Install the Android SDK and ADT Plugin with Eclipse
3. [Optional] Install CDT plugin for Eclipse
4. Download and extract the Android NDK
5. Install Cygwin 1.7.x or above

Note: Don't extract in a folder where folder name is having spaces in between words.
Example:
"Program Files" -- Don't Use
"ProgramFiles" -- Use

Configuration:
Please make sure that you have set the environment variables like

• JAVA_HOME -- Java Home Directory
• NDK_HOME -- Android NDK Home Directory
• Update Path Variable with JDK Bin folder

Creating Android Application

• In Eclipse, Select File->New->Android Project

• Enter the Project Name and Click on "Next" button

• Select the "Build Target", I opted for Android 2.2, SDK 8 Version and Click on "Next" button

• In Application Info dialog, enter the "Package Name" and Select "Finish" button

• Now, you can see the newly created SampleNDK project in the eclipse project explorer window

Example:

• Eclipse Workspace Folder: D:\Workspace
• Android Application Name: SampleNDK
• Android Application Working Folder: D:\Workspace\SampleNDK
• Package Name: com.samplendk
• Android Application Source Folder: D:\Workspace\SampleNDK\src

Source of AndroidNDKActivity.java

package com.samplendk;

import android.app.Activity;
import android.app.AlertDialog;
import android.os.Bundle;

public class SampleNDKActivity extends Activity {
   
    //Declare the native method
    private native String invokeNativeFunction();
   
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        //Call the native methods
        String hello = invokeNativeFunction();
        new AlertDialog.Builder(this).setMessage(hello).show();
    }
   
}

• Create a folder named "jni" in the project

• Right click on the "SampleNDK" project-> Select "New"-> Select "Folder"->Type "jni"

• Create files "Android.mk" and "native.c" in Jni folder

• Right click on the "jni" folder-> Select "New"-> Select "File"->Type "Android.mk"
• Right click on the "jni" folder-> Select "New"-> Select "File"->Type "native.c"

• After Creating those folder and files, the project explorer window look like this

• Do some continuous steps.

• Build, Refresh, and Clean project

• Right Click on the "SampleNDK" project and Select the "Build Project"

• Select "Sample NDK" project and Click "F5" button on keyboard

• Select "Project" menu and Select "Clean" option

• Create header file of the java file

• In windows command prompt, change to project source directory

• Syntax:

• cmd>

• cmd> cd ProjectDir/src

• Example:

• cmd> D:

• D:\> cd SampleNDK/src

• Run the Javah command to create header file

• Syntax:

• cmd> javah -jni .javafile_without_.java_extension // JDK 1.7

• cmd> javah -classpath ..\bin\classes .javafile_without_.java_extension //JDK1.6

• Example:

• D:\SampleNDK\src> javah -jni com.samplendk.SampleNDKActivity //JDK1.7

• D:\SampleNDK\src> javah -classpath ..\bin\classes com.samplendk.SampleNDKActivity //JDK1.6

• Note:

• Don't include the .java at the end of javah command

• Copy the created java header file to jni folder

• D:\SampleNDK\src> copy com_samplendk_SampleNDKActivity.h ..\jni

• Go to Eclipse and Refresh the project by pressing "F5" on keyboard.

• Open the header file from jni folder

• Copy the function created by javah as shown below

• Paste the code in native.c and change the code similar to this

Source of native.c

#include <string.h>
#include "com_samplendk_SampleNDKActivity.h"

jstring JNICALL Java_com_samplendk_SampleNDKActivity_invokeNativeFunction
  (JNIEnv *env, jobject obj)
{
    return (*env)->NewStringUTF(env, "Hello from native function !!");
}

Source of Android.mk

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# Here we give our module name and source file(s)
LOCAL_MODULE := SampleNDK
LOCAL_SRC_FILES := native.c

include $(BUILD_SHARED_LIBRARY)

• Run Cygwin.bat file in the Cygwin installed directory

• It will open the cygwin command prompt

• Change the directory to SampleNDK project directory

• Note: All the drives in your systems are mounted to some directory in the cygwin.

• To see your drive mount points type mount

• # mount

• # cd /cygdrive/d/SampleNDK/

• Run the ndk-build command from the android ndk directory

• # /cygdrive/d/android-ndk-r7/ndk-build

• Error(Only in Android-ndk-r7):

• You may get some error like the following

• /awk.exe: can't open file check-awk.awk

• Andoid NDK: Host 'awk' tool is outdated. Please define

• HOST-Awk to Point to Gawk or Nawk !

• Resolution:

• Goto the android-ndk/prebuilt/windows/bin/

• Change the awk.exe to awk_.exe

• Now you may see the following output after successful execution

• After successful creating libSampleNDK.so file, refresh your Eclipse project

• You can see the updated "Project Explorer" with "libs" folder in the tree hierarchy

• Update the java source code now by adding this library to it

Source code of SampleNDKActivity.java

package com.samplendk;

import android.app.Activity;
import android.app.AlertDialog;
import android.os.Bundle;

public class SampleNDKActivity extends Activity {
   
    static
    {
        System.loadLibrary("SampleNDK");
    }
   
    //Declare the native method
    private native String invokeNativeFunction();
   
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        //Call the native methods
        String hello = invokeNativeFunction();
        new AlertDialog.Builder(this).setMessage(hello).show();
    }
   
}

• Clean the project by Selecting "Project"->"Clean"

• Run the application as "Android Application"

• Note:

• Error:

• java.lang.unsatisfiedLinkError Library -- not found

• Resolution:

• Please see if you have added the "lib" in java source before adding the library in System.loadLibrary() method
• Please find the screenshot of above running program in emulator

If you have queries, please mail to psrdotcom@gmail.com