android Studio 安装NDK+CMake过程

项目需要使用jni开发，之前电脑没有安装过相关工具，现在咱们从头开始。

1，安装NDK和CMake,在Android Studio界面Ctrl+Alt+S进到settings界面，选中CMake和NDK,点击Apply,会自动安装

2，在项目中新建myJNI.java文件，和MainActivity同级目录就行，如图

3，编辑myJNI.java文件，代码如下：

package com.example.myapplication;

public class myJNI {

    static {
        System.loadLibrary("JniTest");
    }
    
    public static native String sayHello();
}

4，点击Android Studio的Terminal,进入终端，执行命令javac myJNI.java,会在目录里生成一个myJNI.class

5,然后执行javac -h myJNI.java,会生成一个头文件

6,新建一个文件夹jni,并且新建一个c文件main.c

7,将刚刚生成的com_example_myapplication_myJNI.h文件中方法实现后，拷贝到main.c中，代码如下：

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

#ifndef _Included_com_example_myapplication_myJNI
#define _Included_com_example_myapplication_myJNI
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_example_myapplication_myJNI
 * Method:    sayHello
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_example_myapplication_myJNI_sayHello
  (JNIEnv *env, jclass jobject){
    return (*env)->NewStringUTF(env,"Hello Maybe");
  }

#ifdef __cplusplus
}
#endif
#endif

8，在app路径下新建文件CMakeLists.txt,并配置该文件,

CMakeLists.txt文件代码如下：

# 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.  设置生成so文件名
            JniTest

            # Sets the library as a shared library.
            SHARED

            # Provides a relative path to your source file(s).  要编译的C/C++文件
            src/main/jni/main.c)

# 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. 指定连接的目标库
                      JniTest

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

9，配置app的build.gradle，在defaultConfig内添加如下代码：