本文源码：https://github.com/jt1024/JNIBasicForAndroid

环境

1.Android Studio 3.0
2.gradle-4.1-all
3.android sdk 26

一、在Android Studio 新建安卓工程

二、基本配置

1.配置ndk，如果没有安装，需要先安装ndk。ndk.dir=“ndk实际路径”

ndk01.png

2.改写build.gradle文件

ndk02.png
3.创建cpp文件夹、hello_lib.cpp、CMakeLists.txt
ndk03.png

三、编写代码

1.编写C++文件 hello_lib.cpp
路径：NDKFirstDemo/app/src/main/cpp/hello_lib.cpp

//
// Created by tao1024 on 2018/3/15.
//

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

extern "C"
JNIEXPORT jstring

JNICALL
Java_com_tao_ndkfirstdemo_Java2CJNI_Java2C(JNIEnv *env, jobject instance) {

    return env->NewStringUTF("Hello world !");
}

2.编写Jave文件 Java2CJNI
路径：NDKFirstDemo/app/src/main/java/com.tao.ndkfirstdem.Java2CJNI

package com.tao.ndkfirstdemo;

/**
 * 作者： 麦典威
 * 修改时间：2018/3/15 0:02
 * 版权声明：www.ekwing.com
 * 功能： ${TODO}
 */


public class Java2CJNI {

    static {
        System.loadLibrary("hello_lib");
    }

    public native String Java2C();
}

3.编写Activity文件 HelloActivity
路径：NDKFirstDemo/app/src/main/java/com.tao.ndkfirstdemo.HelloActivity

package com.tao.ndkfirstdemo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class HelloActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_hello);
        Button btnJni = findViewById(R.id.btn_jni);
        btnJni.setOnClickListener(new View.OnClickListener() Java2CJNI   @Override
            public void onClick(View v) {
 Java2CJNIo    String result = new Java2CJNI().Java2C();
                Toast.makeText(HelloActivity.this, result, Toast.LENGTH_LONG).show();
            }
        });
    }
}

4.编写 activity_hello.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.tao.ndkfirstdemo.HelloActivity">

    <Button
        android:id="@+id/btn_jni"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Java to C"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

5.编写CMakeLists.txt文件，以后如果编写其他jni类，只需替换里面的“hello_lib”

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

add_library( # Sets the name of the library.
             hello_lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/hello_lib.cpp )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                       hello_lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

四、编译

点击build——>Rebuild Project

ndk04.png

编译结束之后，回编译出对应的 .so 文件，如图

ndk05.png

五、运行程序

ndk06.jpg