Android studio jni 入门helloworld

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最近忙着面试，基本上每个面试官都会问一句会不会jni?会不会ndk？像我这么厉害的c和c++，难道真的要荒废了吗，说了你会别人又不听，那么我就得写个jni来试试了，说了这么多，要不是一本正经的胡言乱语我差点都信了话不多说开始撸码
1：先建一个as project 这个就省略了，太难了你们自己摸索
2: 建一个类名字叫myJNI

package com.bril.jni;/** * Created by brill on 2016/9/8. */public class myJNI {    static {        System.loadLibrary("JniTest");    }    public static native String sayHello();}

对了先看下我的目录结构
这里写图片描述
我们继续
3:打开terminal 定位到这个位置输入 javac生成class文件
C:\android\TestWork\Jni\app\src\main\java\com\bril\jni>javac myJNI.java
4:使用javah生成.h文件 cd.. 到com的上层目录

C:\android\TestWork\Jni\app\src\main\java>javah -jni com.bril.jni.myJNI

发现在java目录下生成了.h文件
这里写图片描述
然后 new ->folder->jnifolder 然后勾点点选择finish
4：然后new -> c/c++ source file 输入main 生成main.c
5:把那个生成的文件内容全部拷进来实现里面的

JNIEXPORT jstring JNICALL Java_com_bril_jni_myJNI_sayHello  (JNIEnv *, jclass);

Java_com_bril_jni_myJNI_sayHello根据每个人的项目路径名不同实现这个方法为

JNIEXPORT jstring JNICALL Java_com_bril_jni_myJNI_sayHello        (JNIEnv *env, jclass jobj){    return (*env)->NewStringUTF(env,"vvvv lq");}

6:再新建一个c/c++ source file 因为android studio的bug 必须下面放两个文件所以。。。。
7 在app 下的gradle文件下添加

 ndk {            moduleName "JniTest"            ldLibs "log", "z", "m"            abiFilters "armeabi", "armeabi-v7a", "x86"        }

我的gradle文件

apply plugin: 'com.android.application'android {    compileSdkVersion 24    buildToolsVersion "23.0.3"    defaultConfig {        applicationId "com.bril.jni"        minSdkVersion 15        targetSdkVersion 24        versionCode 1        versionName "1.0"        ndk {            moduleName "JniTest"            ldLibs "log", "z", "m"            abiFilters "armeabi", "armeabi-v7a", "x86"        }    }    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'        }    }    sourceSets { main { jni.srcDirs = ['src/main/jni', 'src/main/jni/'] } }}dependencies {    compile fileTree(dir: 'libs', include: ['*.jar'])    testCompile 'junit:junit:4.12'    compile 'com.android.support:appcompat-v7:24.2.0'}

8:rebuild生成.so文件 build->rebuild project
这里写图片描述
9在main文件夹下建立 jinLIB文件夹把.so按文件夹复制进去

10调用jni

package com.bril.jni;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.widget.TextView;public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        TextView text = (TextView) findViewById(R.id.txt);        text.setText(myJNI.sayHello());    }}

如果其中报错的话看看 local.properties 和 gradle.properties
local.properties 文件

## This file is automatically generated by Android Studio.# Do not modify this file -- YOUR CHANGES WILL BE ERASED!## This file must *NOT* be checked into Version Control Systems,# as it contains information specific to your local configuration.## Location of the SDK. This is only used by Gradle.# For customization when using a Version Control System, please read the# header note.#Thu Sep 08 10:12:30 SGT 2016ndk.dir=C\:\\android\\sdk\\ndk-bundlesdk.dir=C\:\\android\\sdk

gradle.properties 文件

## Project-wide Gradle settings.## For more details on how to configure your build environment visit# http://www.gradle.org/docs/current/userguide/build_environment.html## Specifies the JVM arguments used for the daemon process.# The setting is particularly useful for tweaking memory settings.# Default value: -Xmx10248m -XX:MaxPermSize=256m# org.gradle.jvmargs=-Xmx2048m -XX:MaxPermSize=512m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8## When configured, Gradle will run in incubating parallel mode.# This option should only be used with decoupled projects. More details, visit# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects# org.gradle.parallel=true#Thu Sep 08 10:34:51 SGT 2016android.useDeprecatedNdk=true

项目代码：https://github.com/usernameli/JniTest

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