Android NDK Sample

Create a regular Android project.

The project has a package name of com.miles.ndk with a default Activity name of

AndroidNDKSample1Activity

In Linux,

Create a ndk1 directory, and create a directory name jni in this directory.

Like this:

/var/tmp/miles/ndk1

/var/tmp/miles/ndk1/jni

add native.c in /var/tmp/miles/ndk1/jni

add Android.mk in /var/tmp/miles/ndk1/jni

native.c ==>

// -----------------------------------------------------

#include <jni.h>
#include <string.h>
#include <android/log.h>

#define DEBUG_TAG "NDK_AndroidNDKSample1Activity"

void Java_com_miles_ndk_AndroidNDKSample1Activity_helloLog(JNIEnv * env, jobject this, jstring logThis)

{

    jboolean isCopy;

    const char * szLogThis = (*env)->GetStringUTFChars(env, logThis, &isCopy);

    __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "NDK:LC: [%s]", szLogThis);

    (*env)->ReleaseStringUTFChars(env, logThis, szLogThis);

}

// ----------------------------------------------------

Android.mk ==>

// ----------------------------------------------------

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_LDLIBS := -llog

LOCAL_MODULE    := ndk1

LOCAL_SRC_FILES := native.c

include $(BUILD_SHARED_LIBRARY)

// -----------------------------------------------------

cd /var/tmp/miles/ndk1

/var/tmp/miles/android/NDK/android-ndk-r8/ndk-build

copy /var/tmp/miles/ndk1/libs to Android directory

// ======================================================

AndroidNDKSample1Activity.java ==>

package com.miles.ndk;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.TextView;

public class AndroidNDKSample1Activity extends Activity {

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState) {

       super.onCreate(savedInstanceState);

       setContentView(R.layout.main);

    }

    public void but1_onclick(View v){

       TextView tv = (TextView)findViewById(R.id.textView1);

       tv.setText("Hello World!!");

       helloLog("This will log to LogCat via the native call.");

    }

    private native void helloLog(String logThis);

    static {

       System.loadLibrary("ndk1");

    }

}

// =====================================================

main.xml ⇒

// =====================================================

   <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:weightSum="1">
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello"
    />
<Button android:text="Button" android:id="@+id/button1" android:layout_height="wrap_content" android:onClick="but1_onclick" android:layout_width="wrap_content"></Button>

<TextView android:text="TextView" android:layout_weight="0.08" android:id="@+id/textView1" android:layout_height="wrap_content" android:layout_width="99dp"></TextView>

</LinearLayout>