Android JNI开发从0到1，java调C，C调Java，保姆级教程详解
前些天发现了一个蛮有意思的人工智能学习网站,8个字形容一下"通俗易懂，风趣幽默"，感觉非常有意思,忍不住分享一下给大家。
点击跳转到教程
第一步首先配置Android studio的NDK开发环境，首先在Android studio中下载NDK包
第二步在local.properties文件中，配置对应的NDK路径
第三歩，在app目录下的build.gradle文件中的，android{}闭包中，指定CMakeLists.txt路径
// 在android节点下
// 指定CMakeLists.txt路径
externalNativeBuild {
cmake {
// 在该文件种设置所要编写的c源码位置，以及编译后so文件的名字
path 'CMakeLists.txt'
}
}
在defaultConfig闭包下配置
// 增加cmake控制属性
externalNativeBuild {
cmake {
// 指定编译架构
abiFilters 'arm64-v8a', 'armeabi-v7a', 'x86', 'x86_64'
}
}
在app目录下，指定CmakeLists.txt文件，根据注释进行相应添加
# CMakeLists.txt
# 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.
#CMakeLists.txt
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.
add_library(
# 设置so文件名称.
Hello
# 设置这个so文件为共享.
SHARED
# Provides a relative path to your source file(s).
src/main/jni/Hello.c)
add_library(
# 设置so文件名称.
Test
# 设置这个so文件为共享.
SHARED
# Provides a relative path to your source file(s).
src/main/jni/Test.c)
add_library(
# 设置so文件名称.
CCallJava
# 设置这个so文件为共享.
SHARED
# Provides a relative path to your source file(s).
src/main/jni/CCallJava.c)
# 添加 log 库的链接
target_link_libraries(CCallJava log)
target_link_libraries(Test log)
# 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.
# 制定目标库.
Hello
# Links the target library to the log library
# included in the NDK.
${log-lib} )
第四步，首先进行Java代码C代码的操作
1.JNI2.java代码如下
/**
* @Author: ly
* @Date: 2023/8/6
* @Description: java调C代码
*/
public class JNI2 {
static {
System.loadLibrary("Test"); //加载动态链接库
}
/**
* 让C代码做加法运算,把结果返回
* 场景：大量运算，编解码之类的，需要性能很高的情况下，可以用C代码
*
* @param x
* @param y
* @return
*/
public native int add(int x, int y);
/**
* 从java传入字符串，C代码进行拼接
*
* @param s I am from java
* @return I am from java and I am from c
*/
public native String sayHello(String s);
/**
* 让C代码给每个元素都加上10
*
* @param intArray
* @return
*/
public native int[] increaseArrayEles(int[] intArray);
/**
* 应用：检查密码是否正确，如果正确返回200，否则返回400
*
* @param pwd
* @return
*/
public native int checkPwd(String pwd);
}
2.根据命令行javah +JNI2的全类名，生成Test.c对应的C代码头文件com_example_jniproject_JNI2.h
/* DO NOT EDIT THIS FILE - it is machine generated */
#include 3.根据jni协议，去写对应的c代码，创建Test.c文件，代码如下
//
// Created by DELL on 2023/8/6.
//
#include "com_example_jniproject_JNI2.h"
#include "string.h"
#include 第五步，C代码调用Java代码，首先创建JNI3.java
/**
* @Author: ly
* @Date: 2023/8/6
* @Description: C代码调用Java代码
*/
public class JNI3 {
static {
System.loadLibrary("CCallJava"); //加载动态链接库
}
//当执行这个方法的时候，让C代码调用
//public int add(int x, int y)
public native void callbackAdd();
/**
* 当执行这个方法的时候，让C代码调用
* public void helloFromJava()
*/
public native void callbackHelloFromJava();
/**
* 当执行这个方法的时候，让C代码调用
* public void printString(String s)
*/
public native void callbackPrintString();
/**
* 当执行这个方法的时候，让C代码调用
* public static void sayHello(String s)
*/
public native void callbackSayHello();
public int add(int x, int y) {
Log.e("TAG", "add() x=" + x + " y=" + y);
return x + y;
}
public void helloFromJava() {
Log.e("TAG", "helloFromJava");
}
public void printString(String s) {
Log.e("TAG", "C中输入的：" + s);
}
public static void sayHello(String s) {
Log.e("TAG", "我是java代码中的JNI" +
".java中的sayHello(String s)静态方法,我被C调用了：" + s);
}
}
2.根据命令行，javah +JNI3全类名，生成CCallJava.c对应的头文件
com_example_jniproject_JNI3.h
/* DO NOT EDIT THIS FILE - it is machine generated */
#include 3.对应的CCallJava.c文件中的代码如下
//
// Created by DELL on 2023/8/6.
//
#include "com_example_jniproject_JNI3.h"
#include 之后，在MainActivity中调用对应的方法即可
public class MainActivity extends AppCompatActivity {
private JNI2 jin2;
private static final String TAG = "MainActivity";
private JNI3 mJNI3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
jin2 = new JNI2();
mJNI3 = new JNI3();
}
/******以下是Java代码调用C*****/
public void checkPwd(View view) {
int result = jin2.checkPwd("12345678");
Log.i(TAG, "result==" + result);
}
public void increaseArrayEles(View view) {
int array[] = {1, 2, 3, 4};
jin2.increaseArrayEles(array);
for (int i = 0; i < array.length; i++) {
Log.i(TAG, "result[" + i + "]:" + array[i]);
}
}
public void sayHello(View view) {
String result = jin2.sayHello("I am from java");
Log.i(TAG, "result==" + result);
}
public void add(View view) {
int result = jin2.add(99, 1);
Log.i(TAG, "result==" + result);
}
/******以下是C调Java代码*****/
public void callbackAdd(View view) {
mJNI3.callbackAdd();
}
public void callbackHelloFromJava(View view) {
mJNI3.callbackHelloFromJava();
}
public void callbackPrintString(View view) {
mJNI3.callbackPrintString();
}
public void callbackSayHello(View view) {
mJNI3.callbackSayHello();
}
}
点击按钮便可输出对应的日志，表示调用成功。
