android ndk 入门2 - 基本方法实现

 新建工程NDKTest，新建一个空Activity

新建java类MyNDK.java:

package com.zj.ndktest;

/**
 * Created by root on 15-11-25.
 */
public class MyNDK {
    static {
        System.loadLibrary("hello-jni");
    }

    public static native String Hello();
}

local.properties上加入：

sdk.dir=/opt/android-sdk-linux
ndk.dir=/opt/android-ndk-r10e

app/build.gradle上加入：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        applicationId "com.zj.ndktest"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"

        ndk { 
            moduleName "hello-jni"
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.0'
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

MainActivity.java:

package com.zj.ndktest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.widget.TextView;

public class MainActivity extends Activity {

    private TextView mTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        mTextView = (TextView)findViewById(R.id.text_view);
        mTextView.setText(MyNDK.Hello());
    }
}

点击MyNDK.java文件，右键点击External Tools->javah（没有的请查看android ndk 入门 - 一个简单的ndk工程）

生成app/src/main/jni/com_zj_ndktest_MyNDK.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_zj_ndktest_MyNDK */

#ifndef _Included_com_zj_ndktest_MyNDK
#define _Included_com_zj_ndktest_MyNDK
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    Hello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
  (JNIEnv *, jclass);

#ifdef __cplusplus
}
#endif
#endif

新建jni/Android.mk:

LOCAL_PATH := ${call my-dir}
include $(CLEAR_VARS)
LOCAL_MODULE := hello-jni
LOCAL_SRC_FILES := main.cpp
include ${BUILD_SHARED_LIBRARY}

新建main.cpp:

#include <jni.h>
#include "com_zj_ndktest_MyNDK.h"

JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
        (JNIEnv *env, jclass cla) {
    return env->NewStringUTF("Hello JNI");
}

运行，即可完成简单的ndk程序

####################################################################

实现int输入，int输出

在MyNDK.java上加入：

    public static native int HelloIntegerAdd(int a, int b);

    public static native int HelloIntegerSubtract(int a, int b);

    public static native int HelloIntegerMultiply(int a, int b);

    public static native int HelloIntegerDivide(int a, int b);

在activity_main.xml上加入：

    <TextView
        android:id="@+id/text_integer_add"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_integer_subtarct"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_integer_multiply"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_integer_divide"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

在MainActivity上加入：

package com.zj.ndktest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.widget.TextView;

public class MainActivity extends Activity {

    private TextView mTextView;
    private TextView mTextIntegerAdd;
    private TextView mTextIntegerSubtract;
    private TextView mTextIntegerMultiply;
    private TextView mTextIntegerDivide;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        mTextView = (TextView)findViewById(R.id.text_view);
        mTextView.setText(MyNDK.Hello());

        StringBuffer text_integer_add = new StringBuffer("3 + 5 =");
        text_integer_add.append(MyNDK.HelloIntegerAdd(3, 5));
        mTextIntegerAdd = (TextView)findViewById(R.id.text_integer_add);
        mTextIntegerAdd.setText(text_integer_add.toString());

        StringBuffer text_integer_subtract = new StringBuffer("33 - 100 = ");
        text_integer_subtract.append(MyNDK.HelloIntegerSubtract(33, 100));
        mTextIntegerSubtract = (TextView)findViewById(R.id.text_integer_subtarct);
        mTextIntegerSubtract.setText(text_integer_subtract.toString());

        StringBuffer text_integer_multiply = new StringBuffer("6 * 23 = ");
        text_integer_multiply.append(MyNDK.HelloIntegerMultiply(6, 23));
        mTextIntegerMultiply = (TextView)findViewById(R.id.text_integer_multiply);
        mTextIntegerMultiply.setText(text_integer_multiply.toString());

        StringBuffer text_integer_divide = new StringBuffer("90 / 32 = ");
        text_integer_divide.append(MyNDK.HelloIntegerDivide(90, 32));
        mTextIntegerDivide = (TextView)findViewById(R.id.text_integer_divide);
        mTextIntegerDivide.setText(text_integer_divide.toString());
    }
}

点击MyNDK.java，右键->External Tools->javah

生成新的com_zj_ndktest_MyNDK.h：

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_zj_ndktest_MyNDK */

#ifndef _Included_com_zj_ndktest_MyNDK
#define _Included_com_zj_ndktest_MyNDK
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    Hello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
  (JNIEnv *, jclass);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerAdd
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerAdd
  (JNIEnv *, jclass, jint, jint);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerSubtract
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerSubtract
  (JNIEnv *, jclass, jint, jint);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerMultiply
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerMultiply
  (JNIEnv *, jclass, jint, jint);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerDivide
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerDivide
  (JNIEnv *, jclass, jint, jint);

#ifdef __cplusplus
}
#endif
#endif

main.cpp修改为：

#include <jni.h>
#include "com_zj_ndktest_MyNDK.h"

JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
        (JNIEnv *env, jclass cla) {
    return env->NewStringUTF("Hello JNI");
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerAdd
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerAdd
        (JNIEnv *env, jclass cla, jint a, jint b) {
    jint c;
    c = a + b;

    return c;
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerSubtract
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerSubtract
        (JNIEnv *env, jclass cla, jint a, jint b) {
    jint c;
    c = a - b;

    return c;
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerMultiply
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerMultiply
        (JNIEnv *env, jclass cla, jint a, jint b) {
    jint c;
    c = a * b;

    return c;
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloIntegerDivide
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zj_ndktest_MyNDK_HelloIntegerDivide
        (JNIEnv *env, jclass cla, jint a, jint b) {
    jint c;
    c = a / b;

    return c;
}

运行：

############################################################################################3

实现double输入，double输出

修改MyNDK.java如下：

package com.zj.ndktest;

/**
 * Created by root on 15-11-25.
 */
public class MyNDK {
    static {
        System.loadLibrary("hello-jni");
    }

    public static native String Hello();

    public static native double HelloDoubleAdd(double a, double b);

    public static native double HelloDoubleSubtract(double a, double b);

    public static native double HelloDoubleMultiply(double a, double b);

    public static native double HelloDoubleDivide(double a, double b);
}

修改activity_main.xml如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_double_add"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_double_subtarct"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_double_multiply"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_double_divide"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

修改MainActivity.java如下：

package com.zj.ndktest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.widget.TextView;

public class MainActivity extends Activity {

    private TextView mTextView;
    private TextView mTextDoubleAdd;
    private TextView mTextDoubleSubtract;
    private TextView mTextDoubleMultiply;
    private TextView mTextDoubleDivide;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        mTextView = (TextView)findViewById(R.id.text_view);
        mTextView.setText(MyNDK.Hello());

        StringBuffer text_double_add = new StringBuffer("3.0 + 5.0 =");
        text_double_add.append(MyNDK.HelloDoubleAdd(3.0, 5.0));
        mTextDoubleAdd = (TextView)findViewById(R.id.text_double_add);
        mTextDoubleAdd.setText(text_double_add.toString());

        StringBuffer text_double_subtract = new StringBuffer("33.0 - 100.0 = ");
        text_double_subtract.append(MyNDK.HelloDoubleSubtract(33.0, 100.0));
        mTextDoubleSubtract = (TextView)findViewById(R.id.text_double_subtarct);
        mTextDoubleSubtract.setText(text_double_subtract.toString());

        StringBuffer text_double_multiply = new StringBuffer("6.0 * 23.0 = ");
        text_double_multiply.append(MyNDK.HelloDoubleMultiply(6.0, 23.0));
        mTextDoubleMultiply = (TextView)findViewById(R.id.text_double_multiply);
        mTextDoubleMultiply.setText(text_double_multiply.toString());

        StringBuffer text_double_divide = new StringBuffer("90.0 / 32.0 = ");
        text_double_divide.append(MyNDK.HelloDoubleDivide(90.0, 32.0));
        mTextDoubleDivide = (TextView)findViewById(R.id.text_double_divide);
        mTextDoubleDivide.setText(text_double_divide.toString());
    }
}

点击MyNDK.java，右键->External Tools->javah，生成新的com_zj_ndktest_MyNDK.h:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_zj_ndktest_MyNDK */

#ifndef _Included_com_zj_ndktest_MyNDK
#define _Included_com_zj_ndktest_MyNDK
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    Hello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
  (JNIEnv *, jclass);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleAdd
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleAdd
  (JNIEnv *, jclass, jdouble, jdouble);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleSubtract
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleSubtract
  (JNIEnv *, jclass, jdouble, jdouble);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleMultiply
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleMultiply
  (JNIEnv *, jclass, jdouble, jdouble);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleDivide
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleDivide
  (JNIEnv *, jclass, jdouble, jdouble);

#ifdef __cplusplus
}
#endif
#endif

修改main.cpp如下：

#include <jni.h>
#include "com_zj_ndktest_MyNDK.h"

JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
        (JNIEnv *env, jclass cla) {
    return env->NewStringUTF("Hello JNI");
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleAdd
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleAdd
        (JNIEnv *env, jclass cla, jdouble a, jdouble b) {
    jdouble c;
    c = a + b;

    return c;
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleSubtract
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleSubtract
        (JNIEnv *env, jclass cla, jdouble a, jdouble b) {
    jdouble c;
    c = a - b;

    return c;
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleMultiply
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleMultiply
        (JNIEnv *env, jclass cla, jdouble a, jdouble b) {
    jdouble c;
    c = a * b;

    return c;
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleDivide
 * Signature: (DD)D
 */
JNIEXPORT jdouble JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleDivide
        (JNIEnv *env, jclass cla, jdouble a, jdouble b) {
    jdouble c;
    c = a / b;

    return c;
}

运行：

###################################################################

输入boolean，输出boolean

修改MyNDK.java如下：

package com.zj.ndktest;

/**
 * Created by root on 15-11-25.
 */
public class MyNDK {
    static {
        System.loadLibrary("hello-jni");
    }

    public static native String Hello();

    public static native boolean HelloBoolean(boolean b);
}

修改activity_main.xml如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_boolean_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

修改MainActivity.java如下：

package com.zj.ndktest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.widget.TextView;

public class MainActivity extends Activity {

    private TextView mTextView;
    private TextView mTextBoolean;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        mTextView = (TextView)findViewById(R.id.text_view);
        mTextView.setText(MyNDK.Hello());

        StringBuffer text_boolean = new StringBuffer("True = ");
        text_boolean.append(MyNDK.HelloBoolean(true));
        mTextBoolean = (TextView)findViewById(R.id.text_view);
        mTextBoolean.setText(text_boolean.toString());

    }
}

点击MyNDK.java，右键->External Tools->javah，生成com_zj_ndktest_MyNDK.h:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_zj_ndktest_MyNDK */

#ifndef _Included_com_zj_ndktest_MyNDK
#define _Included_com_zj_ndktest_MyNDK
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    Hello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
  (JNIEnv *, jclass);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloBoolean
 * Signature: (Z)Z
 */
JNIEXPORT jboolean JNICALL Java_com_zj_ndktest_MyNDK_HelloBoolean
  (JNIEnv *, jclass, jboolean);

#ifdef __cplusplus
}
#endif
#endif

修改main.cpp如下：

#include <jni.h>
#include "com_zj_ndktest_MyNDK.h"

JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
        (JNIEnv *env, jclass cla) {
    return env->NewStringUTF("Hello JNI");
}

JNIEXPORT jboolean JNICALL Java_com_zj_ndktest_MyNDK_HelloBoolean
        (JNIEnv *env, jclass cla, jboolean b) {
    jboolean res = JNI_FALSE;

    if (b == JNI_TRUE) {
        res = JNI_TRUE;
    } else {
        res = JNI_FALSE;
    }

    return res;
}

运行：

##################################################################################

输入jstring，double，输出jstring

修改MyNDK.java:

package com.zj.ndktest;

/**
 * Created by root on 15-11-25.
 */
public class MyNDK {
    static {
        System.loadLibrary("hello-jni");
    }

    public static native String Hello();

    public static native String sprint(String format, double x);
}

修改activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_string_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

修改MainActivity.java:

package com.zj.ndktest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.widget.TextView;

public class MainActivity extends Activity {

    private TextView mTextView;
    private TextView mTextString;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        mTextView = (TextView)findViewById(R.id.text_view);
        mTextView.setText(MyNDK.Hello());

        mTextString = (TextView)findViewById(R.id.text_string_view);
        mTextString.setText(MyNDK.sprint("Amount due = %8.2f", 33.4556));
    }
}

点击MyNDK.java，右键->External Tools->javah，生成com_zj_ndktest_MyNDK.h:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_zj_ndktest_MyNDK */

#ifndef _Included_com_zj_ndktest_MyNDK
#define _Included_com_zj_ndktest_MyNDK
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    Hello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
  (JNIEnv *, jclass);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    sprint
 * Signature: (Ljava/lang/String;D)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_sprint
  (JNIEnv *, jclass, jstring, jdouble);

#ifdef __cplusplus
}
#endif
#endif

修改main.cpp如下：

#include <jni.h>
#include <stdlib.h>
#include <stdio.h>
#include "com_zj_ndktest_MyNDK.h"

JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
        (JNIEnv *env, jclass cla) {
    return env->NewStringUTF("Hello JNI");
}

JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_sprint
        (JNIEnv *env, jclass cla, jstring format, jdouble x) {
    const char* cformat;
    jstring ret;

    cformat = env->GetStringUTFChars(format, NULL);
    char *cret;
    cret = (char*)malloc(strlen(cformat)+8);
    sprintf(cret, cformat, x);
    ret = env->NewStringUTF(cret);
    free(cret);
    env->ReleaseStringUTFChars(format, cformat);

    return ret;
}

运行：

#############################################################

访问实例域

删除MyNDK.java文件，新建Employee.java文件：

package com.zj.ndktest;

/**
 * Created by root on 15-11-25.
 */
public class Employee {

    static {
        System.loadLibrary("hello-employee");
    }

    private String name;
    private double salary;

    public Employee(String n, double s) {
        name = n;
        salary = s;
    }

    public native void raiseSalary(double byPercent);

    public String print() {
        StringBuffer sb = new StringBuffer();
        sb.append(name);
        sb.append(" ");
        sb.append(salary);
        return sb.toString();
    }
}

修改activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_instance_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

修改MainAcitvity.java：

package com.zj.ndktest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.widget.TextView;

public class MainActivity extends Activity {

    private TextView mTextInstance;;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        Employee em = new Employee("hello world", 32000);
        em.raiseSalary(5);

        mTextInstance = (TextView)findViewById(R.id.text_instance_view);
        mTextInstance.setText(em.print());
    }
}

修改app/build.gradle:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        applicationId "com.zj.ndktest"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"

        ndk {
            // moduleName "hello-jni"
            moduleName "hello-employee"
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.0'
}

点击Employee.java，右键->Extrenal Tools->javah，生成com_zj_ndktest_Employee.h:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_zj_ndktest_Employee */

#ifndef _Included_com_zj_ndktest_Employee
#define _Included_com_zj_ndktest_Employee
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_zj_ndktest_Employee
 * Method:    raiseSalary
 * Signature: (D)V
 */
JNIEXPORT void JNICALL Java_com_zj_ndktest_Employee_raiseSalary
  (JNIEnv *, jobject, jdouble);

#ifdef __cplusplus
}
#endif
#endif

修改Android.mk:

LOCAL_PATH := ${call my-dir}
include $(CLEAR_VARS)
LOCAL_MODULE := hello-employee
LOCAL_SRC_FILES := main.cpp
include ${BUILD_SHARED_LIBRARY}

修改main.cpp：

#include <jni.h>
#include <stdlib.h>
#include <stdio.h>
#include "com_zj_ndktest_Employee.h"

JNIEXPORT void JNICALL Java_com_zj_ndktest_Employee_raiseSalary
        (JNIEnv *env, jobject obj, jdouble byPercent) {
    /* get the class */
    jclass class_Employee = env->GetObjectClass(obj);

    /* get the field ID */
    jfieldID id_salary = env->GetFieldID(class_Employee, "salary", "D");

    /* get the field value */
    jdouble salary = env->GetDoubleField(obj, id_salary);

    salary *= 1 + byPercent / 100;

    /* set the field value */
    env->SetDoubleField(obj, id_salary, salary);
}

运行：

######################################################################################

输入double数组，输出double数组

删除Employee.java，新建MyNDK.java:

package com.zj.ndktest;

/**
 * Created by root on 15-11-25.
 */
public class MyNDK {
    static {
        System.loadLibrary("hello-jni");
    }

    public static native String Hello();

    public native double[] HelloDoubleArray(double[] arr);

    public String print(double[] arr) {
        StringBuffer sb = new StringBuffer();

        for(double dou : arr) {
            sb.append(dou);
            sb.append(" ");
        }

        return sb.toString();
    }
}

修改activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_array_view1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_array_view2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

修改MainActivity.java:

package com.zj.ndktest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.widget.TextView;

public class MainActivity extends Activity {

    private TextView mTextView;
    private TextView mTextArray1;
    private TextView mTextArray2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        mTextView = (TextView)findViewById(R.id.text_view);
        mTextView.setText(MyNDK.Hello());

        double[] arr = new double[]{1,2,3,4};
        MyNDK my = new MyNDK();

        mTextArray1 = (TextView)findViewById(R.id.text_array_view1);
        mTextArray1.setText(my.print(arr));

        double[] arr2 = my.HelloDoubleArray(arr);

        mTextArray2 = (TextView)findViewById(R.id.text_array_view2);
        mTextArray2.setText(my.print(arr2));
    }
}

修改app/build.gradle:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        applicationId "com.zj.ndktest"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"

        ndk {
             moduleName "hello-jni"
            //moduleName "hello-employee"
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.0'
}

修改Android.mk:

LOCAL_PATH := ${call my-dir}
include $(CLEAR_VARS)
LOCAL_MODULE := hello-jni
LOCAL_SRC_FILES := main.cpp
include ${BUILD_SHARED_LIBRARY}

点击MyNDK，右键->External Tools->javah，生成com_zj_ndktest_MyNDk.h:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_zj_ndktest_MyNDK */

#ifndef _Included_com_zj_ndktest_MyNDK
#define _Included_com_zj_ndktest_MyNDK
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    Hello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
  (JNIEnv *, jclass);

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleArray
 * Signature: ([D)[D
 */
JNIEXPORT jdoubleArray JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleArray
  (JNIEnv *, jobject, jdoubleArray);

#ifdef __cplusplus
}
#endif
#endif

修改main.cpp:

#include <jni.h>
#include <stdlib.h>
#include <stdio.h>
#include "com_zj_ndktest_Employee.h"

extern "C" {

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    Hello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_zj_ndktest_MyNDK_Hello
        (JNIEnv *env, jclass cla) {
    return env->NewStringUTF("hello world");
}

/*
 * Class:     com_zj_ndktest_MyNDK
 * Method:    HelloDoubleArray
 * Signature: ([D)[D
 */
JNIEXPORT jdoubleArray JNICALL Java_com_zj_ndktest_MyNDK_HelloDoubleArray
        (JNIEnv *env, jobject obj, jdoubleArray dou) {
        jsize leng = env->GetArrayLength(dou);

        jdoubleArray arr = env->NewDoubleArray(leng);
        double *a = env->GetDoubleArrayElements(arr, NULL);

        double *d = env->GetDoubleArrayElements(dou, NULL);

        for (int i = 0; i < leng; i++) {
            a[i] = d[i] * 2;
        }

        env->ReleaseDoubleArrayElements(dou, d, NULL);
        env->ReleaseDoubleArrayElements(arr, a, NULL);

        return arr;
    }

}

运行：