目錄前言1.導(dǎo)入C語言的類2.接著導(dǎo)入Android.mk文件3.我們配置一下build.gradle文件4.好了，此時(shí)可以編譯一下項(xiàng)目了6.將生成的so文件拷入src/main/jniLibs中7.調(diào)用C語言方法的Activity如下總結(jié)前言

做Android開發(fā)的程序員應(yīng)該都知道，Android的開發(fā)語言我們都是在使用JAVA(Kotlin和Flutter我們暫時(shí)不考慮)。但是，有時(shí)候我們也需要使用到C語言進(jìn)行一些功能的開發(fā)。這個(gè)時(shí)候我們就需要用到JNI了。

1.導(dǎo)入C語言的類

首先我們需要把C語言寫的功能類放入我們的項(xiàng)目中。這里我直接從資料中找了一個(gè)，畢竟我不會寫。路徑在src/main/jni中

find_name.cpp

#include <jni.h>#include <string.h> #include <stdio.h>#include <stdlib.h>#include <string.h>#include <netdb.h>#include <sys/stat.h>#include <sys/types.h>#include <sys/select.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h> #define send_MAXSIZE 50#define recv_MAXSIZE 1024 struct NETBIOSNS {unsigned short int tid; //unsigned short int 占2字節(jié)unsigned short int flags;unsigned short int questions;unsigned short int answerRRS;unsigned short int authorityRRS;unsigned short int additionalRRS;unsigned char name[34];unsigned short int type;unsigned short int classe;}; char *getNameFromIp(const char *ip); extern 'C' jstring Java_com_hao_cmake_MainActivity_cpuFromJNI(JNIEnv* env, jobject thiz, jstring ip) {const char* str_ip;str_ip = env->GetStringUTFChars(ip, 0);return env->NewStringUTF(getNameFromIp(str_ip));} char *getNameFromIp(const char *ip) {char str_info[1024] = { 0 };struct sockaddr_in toAddr; //sendto中使用的對方地址struct sockaddr_in fromAddr; //在recvfrom中使用的對方主機(jī)地址char send_buff[send_MAXSIZE];char recv_buff[recv_MAXSIZE];memset(send_buff, 0, sizeof(send_buff));memset(recv_buff, 0, sizeof(recv_buff));int sockfd; //socketunsigned int udp_port = 137;int inetat;if ((inetat = inet_aton(ip, &toAddr.sin_addr)) == 0) {sprintf(str_info, '[%s] is not a valid IP addressn', ip);return str_info;}if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {sprintf(str_info, '%s socket error sockfd=%d, inetat=%dn', ip, sockfd, inetat);return str_info;}bzero((char*) &toAddr, sizeof(toAddr));toAddr.sin_family = AF_INET;toAddr.sin_addr.s_addr = inet_addr(ip);toAddr.sin_port = htons(udp_port); //構(gòu)造netbios結(jié)構(gòu)包struct NETBIOSNS nbns;nbns.tid = 0x0000;nbns.flags = 0x0000;nbns.questions = 0x0100;nbns.answerRRS = 0x0000;nbns.authorityRRS = 0x0000;nbns.additionalRRS = 0x0000;nbns.name[0] = 0x20;nbns.name[1] = 0x43;nbns.name[2] = 0x4b;int j = 0;for (j = 3; j < 34; j++) {nbns.name[j] = 0x41;}nbns.name[33] = 0x00;nbns.type = 0x2100;nbns.classe = 0x0100;memcpy(send_buff, &nbns, sizeof(nbns));int send_num = 0;send_num = sendto(sockfd, send_buff, sizeof(send_buff), 0,(struct sockaddr *) &toAddr, sizeof(toAddr));if (send_num != sizeof(send_buff)) {sprintf(str_info,'%s sendto() error sockfd=%d, send_num=%d, sizeof(send_buff)=%dn',ip, sockfd, send_num, sizeof(send_buff));shutdown(sockfd, 2);return str_info;}int recv_num = recvfrom(sockfd, recv_buff, sizeof(recv_buff), 0,(struct sockaddr *) NULL, (socklen_t*) NULL);if (recv_num < 56) {sprintf(str_info, '%s recvfrom() error sockfd=%d, recv_num=%dn', ip,sockfd, recv_num);shutdown(sockfd, 2);return str_info;}//這里要初始化。因?yàn)榘l(fā)現(xiàn)linux和模擬器都沒問題，真機(jī)上該變量若不初始化，其值就不可預(yù)知unsigned short int NumberOfNames = 0;memcpy(&NumberOfNames, recv_buff + 56, 1);char str_name[1024] = { 0 };unsigned short int mac[6] = { 0 };int i = 0;for (i = 0; i < NumberOfNames; i++) {char NetbiosName[16];memcpy(NetbiosName, recv_buff + 57 + i * 18, 16);//依次讀取netbios nameif (i == 0) {sprintf(str_name, '%s', NetbiosName);}}sprintf(str_info, '%s|%s|', ip, str_name);for (i = 0; i < 6; i++) {memcpy(&mac[i], recv_buff + 57 + NumberOfNames * 18 + i, 1);sprintf(str_info, '%s%02X', str_info, mac[i]);if (i != 5) {sprintf(str_info, '%s-', str_info);}}return str_info;}

這里要注意一點(diǎn)，jstring Java_com_hao_cmake_MainActivity_cpuFromJNI方法中，com_hao_cmake是我們的包名，MainActivity是調(diào)用JNI的Activity名稱，cpuFromJNI是對應(yīng)方法的名字。

2.接著導(dǎo)入Android.mk文件

這個(gè)文件也是放在jni文件夾中

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS) # 指定so庫文件的名稱LOCAL_MODULE := jni_mix# 指定需要編譯的源文件列表LOCAL_SRC_FILES := find_name.cpp# 指定C++的編譯標(biāo)志LOCAL_CPPFLAGS += -fexceptions# 指定要加載的靜態(tài)庫#LOCAL_WHOLE_STATIC_LIBRARIES += android_support# 指定需要鏈接的庫LOCAL_LDLIBS := -llog include $(BUILD_SHARED_LIBRARY)$(call import-module, android/support)3.我們配置一下build.gradle文件

android -> defaultConfig 下添加

externalNativeBuild{ ndkBuild{abiFilters 'arm64-v8a','armeabi-v7a' }}

android 下添加

externalNativeBuild { ndkBuild {path file(’src/main/jni/Android.mk’) }}packagingOptions{ pickFirst ’lib/arm64-v8a/libjni_mix.so’ pickFirst ’lib/armeabi-v7a/libjni_mix.so’}4.好了，此時(shí)可以編譯一下項(xiàng)目了5.此時(shí)我們可以找一下我們生成的so包了

在build → intermediates → ndkBuild → debug → obj → local下，我們可以找到我們生成的相關(guān)配置平臺的so文件

6.將生成的so文件拷入src/main/jniLibs中

這個(gè)樣子的

7.調(diào)用C語言方法的Activity如下

public class MainActivity extends AppCompatActivity { public native String cpuFromJNI(String ip); static {System.loadLibrary('jni_mix'); } @Override protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);String str = cpuFromJNI('192.168.0.163');Toast.makeText(this,str,Toast.LENGTH_SHORT).show(); }}

這樣我們就完成了用C語言類生成so包，并使用JNI進(jìn)行調(diào)用的全流程。

注意：在使用JNI進(jìn)行調(diào)用的時(shí)候，我們的環(huán)境一定要有NDK，這個(gè)我這里就不說了，大家如果沒有搭建需要上網(wǎng)找找搭建一下。

總結(jié)

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