Android Native Development Kit Cookbook

Go to the Oracle Java JDK web page at http://www.oracle.com/technetwork/java/javase/downloads/index.html, and choose JDK6 or above for your platform to download.

Double-click on the downloaded executable, and click through the installation wizard to finish the installation.

Go to Control Panel | System and Security | System | Advanced system settings. A System Properties window will pop up.

Click on the Environment Variables button in the Advanced tab; another Environment Variables window will pop up.

Under System variables, click on New to add a variable with the name as JAVA_HOME and value as the path of the JDK installation root directory. This is shown as follows:

Under System variables, scroll to find the PATH (or Path) environment variable. Insert %JAVA_HOME%\bin; at the beginning of the value. If no PATH or Path variable exists, create a new variable with the value set to %JAVA_HOME%\bin. Click on OK all the way through to dismiss all windows.

To verify whether JDK is installed and configured correctly, start a new command-line console, and enter javac -version. If JDK is configured correctly, you will get the Java version in the output.

Go to http://cygwin.com/install.html to download setup.exe for Cygwin. Double-click on it after the download is complete in order to start the installation.

Click on Next, then select Install from Internet. Keep clicking on Next until you see the Available Download Sites list. Select the site that is close to your location, then click on Next:

Look for GNU make under Devel, ensure it is version 3.81 or later, and gawk under Base. Alternatively, you can search for make and gawk using the Search box. Make sure both GNU make and gawk are selected to install, then click on Next. The installation can take a while to finish:

Start Eclipse. Select Help | Install New Software, and a window titled Install will pop up.

Click on the Add… button at the top-right will corner, and another window titled Add Repository will pop up.

In the Add Repository window, enter ADT for Name and https://dl-ssl.google.com/android/eclipse/ for Location. Then click on OK.

It may take a few seconds for Eclipse to load the software items from the ADT website. After loading, select Developer Tools and NDK Plugins, then click on Next to proceed:

In the next window, a list of tools to be installed will be shown. Simply click on Next. Read and accept all the license agreements, then click on Finish.

After installation finishes, restart Eclipse as prompted.

Download Android SDK from http://developer.android.com/sdk/index.html.

Double-click on the installer to start the installation. Follow the wizard to finish the installation.

In Eclipse, select Window | Preferences to open the Preferences window. Select Android from the left panel, then click on Browse to locate the Android SDK root directory. Click on Apply, and then OK.

Start Android SDK Manager at the Android SDK installation root directory. Select Android SDK Tools, Android SDK Platform-tools, at least one Android platform (the latest is preferred), System Image, SDK Samples, and Android Support. Then click on Install. in the next window, read and accept all the license agreements, then click on Install:

Go to http://developer.android.com/tools/sdk/ndk/index.html to download the latest version of Android NDK. Unzip the downloaded file.

Open Cygwin.bat under the cygwin root directory. It contains the following content by default:

@echo off
C:
chdir C:\cygwin\bin
bash --login -i

Add the following content after @echo off before C:

set IS_UNIX=
set JAVA_HOME=<JDK path>
set PATH=<SDK path>\tools;<NDK path>
set ANDROID_NDK_ROOT=/cygdrive/<NDK path>

As an example, the file content on my machine is as follows; note that Progra~1 is the short name for the Program Files folder:

set IS_UNIX=set JAVA_HOME=c:/Progra~1/Java/jdk1.7.0_05
set PATH=C:/Users/Administrator/AppData/Local/Android/android-sdk/tools;C:/Users/Administrator/Downloads/android-ndk-r8-windows/android-ndk-r8
set ANDROID_NDK_ROOT=/cygdrive/c/Users/Administrator/Downloads/android-ndk-r8-windows/android-ndk-r8

Start Cygwin by double-clicking on cygwin.bat, then go to the samples/hello-jni directory in NDK. Type the command ndk-build. If the build is successful, it proves that the NDK environment is set up correctly:

In Eclipse, select Window | Preferences to open the Preferences window. Click on Android from the left panel, and select NDK from the drop-down list. Click on Browse to locate the Android NDK root directory. Click on OK to dismiss the pop-up window. This enables us to build and debug Android NDK applications with the Eclipse NDK plugin:

Start a terminal, and enter ldd --version. This will print the version of ldd and glibc:

We can execute the library as an application. Start a terminal, locate the library location, and then enter the following command:

<glibc library location>/<glibc library>. 

The following output will be displayed:

We need to enable 32-bit application execution if we are using a 64-bit machine. Start a terminal, and enter the following command:

sudo apt-get install ia32-libs

Install JDK 6 or above. At a terminal, enter the command sudo apt-get install openjdk-6-jdk, or alternatively we can enter sudo apt-get install sun-java6-jdk. After installation, we need to add the JDK path to the PATH environment variable by adding the following lines to ~/.bashrc:

export JDK_PATH=/usr/local/jdk1.7.0/bin
export PATH=$PATH:$JDK_PATH

Follow steps 1 to 6 of the Setting up an Android NDK development environment in Windows recipe to install the ADT plugin for Eclipse.

Download Android SDK from http://developer.android.com/sdk/index.html, then extract the downloaded package.

Append the following lines to ~/.bashrc:

export ANDROID_SDK=<path to Android SDK directory>
export PATH=$PATH:$ ANDROID_SDK/tools:$ANDROID_SDK/platform-tools

Follow steps 9 and 10 of the Setting up an Android NDK development environment in Windows recipe to configure the SDK path at Eclipse, and download additional packages.

Download the latest version of Android NDK from http://developer.android.com/tools/sdk/ndk/index.html, then extract the downloaded file.

Change the lines that you appended to ~/.bashrc in step 3:

export ANDROID_SDK=<path to Android SDK directory>
export ANDROID_NDK=<path to Android NDK directory> 
export PATH=$PATH:$ANDROID_SDK/tools:$ANDROID_SDK/platform-tools:$ANDROID_NDK

Start a new terminal, then go to the samples/hello-jni directory in NDK. Type the command ndk-build. If the build is successful, it proves that the NDK environment is set up correctly:

Follow steps 1 to 6 of the Setting up an Android NDK development environment in Windows recipe to install the ADT plugin for Eclipse.

Download Android SDK from http://developer.android.com/sdk/index.html, then extract the downloaded package.

Append the following lines to ~/.profile. If the file doesn't exist, create a new one. Save the changes and log out of the current session:

export ANDROID_SDK=<path to Android SDK directory>
export PATH=$PATH:$ ANDROID_SDK/tools:$ANDROID_SDK/platform-tools

In Eclipse, select Eclipse | Preferences to open the Preferences window. Select Android from the left panel, then click on Browse to locate the Android SDK root directory. Click on Apply, and then OK.

In a terminal, start the Android SDK Manager at the tools directory by typing the command android. Select Android SDK Tools, Android SDK Platform-tools, at least one Android platform (the latest one is preferred), System Image, SDK Samples, and Android Support. Then click on Install. In the next window, read and accept all the license agreements, then click on Install.

Download Android SDK from http://developer.android.com/sdk/index.html, and then extract the downloaded package.

Change the lines that you appended to ~/.profile in step 3:

export ANDROID_SDK=<path to Android SDK directory>
export ANDROID_NDK=<path to Android NDK directory> 
export PATH=$PATH:$ANDROID_SDK/tools:$ANDROID_SDK/platform-tools:$ANDROID_NDK

Start a new terminal, then go to the samples/hello-jni directory in NDK. Type the command ndk-build. If the build is successful, it proves that the NDK environment is set up correctly.

Go to http://developer.android.com/tools/sdk/ndk/index.html to download the latest version of Android NDK. Unzip the downloaded file.

Open Cygwin.bat under the cygwin root directory. The content should be similar to the following code snippet, if you have previously configured NDK on the system:

@echo off
set IS_UNIX=
set JAVA_HOME=<JDK path>
set PATH=<SDK path>\tools;<NDK path>
set ANDROID_NDK_ROOT=/cygdrive/<NDK path>
C:
chdir C:\cygwin\bin
bash --login -i

Update <NDK path> from the old NDK path to the newly downloaded and decompressed location.

Download the latest version of Android NDK from http://developer.android.com/tools/sdk/ndk/index.html, then extract the downloaded file.

If we have followed the Setting up an Android NDK development environment in Ubuntu Linux recipe, the following content should appear at the end of ~/.bashrc:

export ANDROID_SDK=<path to Android SDK directory>
export ANDROID_NDK=<path to Android NDK directory>
export PATH=$PATH:$ANDROID_SDK/tools:$ANDROID_SDK/platform-tools:$ANDROID_NDK

Update the ANDROID_NDK path to the newly downloaded and extracted Android NDK folder.

Start Eclipse, and select File | New | Android Project. Enter HelloNDK as the value for Project Name. Select Create new project in workspace. Then click on Next:

In the next window, select an Android version that you want to target. Usually, the latest version is recommended. Then click on Next.

In the next window, specify your package name as cookbook.chapter1. Select the Create Activity box, and specify the name as HelloNDKActivity. Set the value for Minimum SDK as 5 (Android 2.0). Click on Finish:

In the Eclipse package explorer, right-click on the HelloNDK project, and select New | Folder. Enter the name jni in the pop-up window, then click on Finish:

Right-click on the newly-created jni folder under the HelloNDK project. Select New | File, enter hello.c as the value for File name, then click on Finish. Type the following code in the hello.c file:

#include <string.h>
#include <jni.h>

jstring 
Java_cookbook_chapter1_HelloNDKActivity_naGetHelloNDKStr(JNIEnv* pEnv,  jobject pObj)
{
    return (*pEnv)->NewStringUTF(pEnv, "Hello NDK!");
}

Right-click on the jni folder. Select New | File, enter Android.mk as the value for File name, then click on Finish. Type the following code in the Android.mk file:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE    := hello
LOCAL_SRC_FILES := hello.c
include $(BUILD_SHARED_LIBRARY)

Start a terminal, go to the jni folder, and type ndk-build to build the hello.c program as a native library.

Edit the HelloNDKActivity.java file. The file should contain the following content:

public class HelloNDKActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView tv = new TextView(this);
        tv.setTextSize(30);
        tv.setText(naGetHelloNDKStr());
        this.setContentView(tv);
    }
    public native String naGetHelloNDKStr();
    static {
        System.loadLibrary("hello");
    }
}

Right-click on the HelloNDK project in Eclipse. Select Run As | Android Application. Your Android phone or emulator will be displayed with something similar to the following screenshot:

Write the Java code, including the native method definition.

Compile the Java code and make sure the class file appears under the bin/classes/ folder of our project.

Start a terminal and go to the jni folder, and enter the following command:

$ javah -classpath ../bin/classes –o <output file name> <java package name>.<java class anme>

In our HelloNDK example, the command should be as follows:

$ javah -classpath ../bin/classes –o hello.h cookbook.chapter1.HelloNDKActivity

This will generate a file named hello.h with its function definition as follows:

JNIEXPORT jstring JNICALL Java_cookbook_chapter1_HelloNDKActivity_naGetHelloNDKStr
  (JNIEnv *, jobject);