NDK-JNI实战教程（一） 在Android Studio运行第一个NDK程序

PS一句：最终还是选择CSDN来整理发表这几年的知识点，该文章平行迁移到CSDN。因为CSDN也支持MarkDown语法了，牛逼啊！

NDK开发，其实是为了项目需要调用底层的一些C/C++的一些东西；另外就是为了效率更加高些。如果你在Eclipse+ADT下开发过NDK就能体会到要么是配置NDK还要下载Cygwin，配置Cygwin ,然后需要编译生成，相当的蛋疼。要么是直接用Eclipse开发，但是前期配置也是一堆；真心蛋疼。但是现在在AS上Eclipse能做到的这边都OK，这边有的Eclipse上没有的，而且Google亲生的支持下只会越来越比Eclipse下开发NDK更加牛逼，所以你还不准备上手吗？

在AS开发NDK JNI也需要配置，不过相当Easy。第一步就是去官方下载个NDK包就可以了，像我的直接放在D盘就行了。关于怎么下载安装看这里 AD NDK会有介绍。

第二步就是就是直接写代码了。哈哈，你没听错，是这样的，方便吧？至于下载下来的NDK怎么和AS工程关联，也就是一行配置的问题，后文有说明带你一步一步体验。

But,还是要有个but，Android Studio还不是个壮年，尤其在NDK开发中，所以本文只是工具性的演示，实质是教会大家NDK开发。

Let’s Go！！！

在AS中新建一个Project，然后再新建一个class为NdkJniUtils，在内部声明native方法（jni使用的定义，后面系列教程会细说）。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">package</span> io.github.yanbober.ndkapplication;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NdkJniUtils</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">native</span> String <span class="hljs-title" style="box-sizing: border-box;">getCLanguageString</span>();
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

在工程主文件Activity中写入如下代码调运JNI的东西显示在UI上。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">MainActivity</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ActionBarActivity</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> TextView mTextView;

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onCreate</span>(Bundle savedInstanceState) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

mTextView = (TextView) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.findViewById(R.id.test);

NdkJniUtils jni = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> NdkJniUtils();

mTextView.setText(jni.getCLanguageString());
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul>

然后build project得到其中中间文件，我们关注的是.class文件。编译OK以后生成的class文件在AS工程的如下目录：

NDKApplication\app\build\intermediates\classes\debug

然后接下来的步骤就是根据生成的class文件，利用javah生成对应的 .h头文件。

点开AS的Terminal标签，默认进入到该项目的app文件夹下。我在windows平台下输入如下命令跳转到class中间文件生成路径：

xxxxx\app> cd build\intermediates\classes\debug

然后执行如下javah命令生成h文件。

xxxxx\debug> javah -jni io.github.yanbober.ndkapplication.NdkJniUtils

执行完之后你可以在文件夹NDKApplication\app\build\intermediates\classes\debug下看见生成的 .h头文件为：

io_github_yanbober_ndkapplication_NdkJniUtils.h

其内容为：

<code class="language-c++ hljs vala has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* DO NOT EDIT THIS FILE - it is machine generated */</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <jni.h></span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* Header for class io_github_yanbober_ndkapplication_NdkJniUtils */</span>

<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#ifndef _Included_io_github_yanbober_ndkapplication_NdkJniUtils</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#define _Included_io_github_yanbober_ndkapplication_NdkJniUtils</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#ifdef __cplusplus</span>
extern <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"C"</span> {
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#endif</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*
* Class:     io_github_yanbober_ndkapplication_NdkJniUtils
* Method:    getCLanguageString
* Signature: ()Ljava/lang/String;
*/</span>
JNIEXPORT jstring<span class="hljs-constant" style="box-sizing: border-box;"> JNICALL </span>Java_io_github_yanbober_ndkapplication_NdkJniUtils_getCLanguageString
(JNIEnv *, jobject);

<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#ifdef __cplusplus</span>
}
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#endif</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#endif</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul>

在工程的main目录下新建一个名字为jni的目录，然后将刚才的 .h文件剪切过来。在jni目录下新建一个c文件，随意取名，我的叫jnitest.c 。然后编辑代码如下（后面会解释啥意思，这里重在工具使用）：

<code class="language-c++ hljs scala has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">#include <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"io_github_yanbober_ndkapplication_NdkJniUtils.h"</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*
* Class:     io_github_yanbober_ndkapplication_NdkJniUtils
* Method:    getCLanguageString
* Signature: ()Ljava/lang/String;
*/</span>
JNIEXPORT jstring JNICALL Java_io_github_yanbober_ndkapplication_NdkJniUtils_getCLanguageString
(JNIEnv *env, j<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">object</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">obj</span>){</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> (*env)->NewStringUTF(env,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"This just a test for Android Studio NDK JNI developer!"</span>);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

接下来在工程的local.properties文件中添加NDK路径（上面下载好的那个NDK），类似其中的SDK路径一样，我的添加后如下：

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">sdk.dir=D\:\\AndroidStdioSDK\\sdk
#add by 工匠若水
ndk.dir=D\:\\AndroidStdioSDK\\android-ndk-r10d-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">64</span>bit</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

接下来在app module目录下的build.gradle中设置库文件名（生成的so文件名）。找到gradle文件的defaultConfig这项，在里面添加如下内容：

<code class="language-groovy hljs lasso has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">defaultConfig {
<span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-attribute" style="box-sizing: border-box;">...</span>
ndk{
moduleName <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"YanboberJniLibName"</span>         <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//生成的so名字</span>
abiFilters <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"armeabi"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"armeabi-v7a"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"x86"</span>  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//输出指定三种abi体系结构下的so库。目前可有可无。</span>
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

现在生成的so库名字也有了，那就去代码的NdkJniUtils java文件添加静态初始化load代码，添加如下：

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> {
System.loadLibrary(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"YanboberJniLibName"</span>);   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//defaultConfig.ndk.moduleName</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

好了，到此AS下NDK JNI开发的代码编写和设置就OK了，接下来就是编译工程运行就可以了。

但是有些电脑好奇怪此时编译会报错，妹的，没辙，后来网上找到答案说这是NDK在Windows下一个bug，当只编译一个单一文件时出现，解决办法就是再添加一个空的文件就行了，这个网站有介绍：NDK在Windows的一个bug。不过你要是刚才能顺利编译就没必要蛋疼这个问题了。

好了，我的编译运行结果如下：



到此为止简单的体验AS下NDK开发的过程就结束了。期待下一篇再续深入。

【工匠若水 http://blog.csdn.net/yanbober】 继续阅读《 NDK-JNI实战教程（二） JNI官方中文资料》 /article/1503777.html