[移动开发]使用JNI和反射实现调用Java方法跳转页面

• 学习JNI使用JNI实现调用Java方法跳转页面
  jni的项目结构如下图，
  CMakeList.txt文件的作用与内用结构
  CMake是一个跨平台的构建工具，可以用简单的语句来描述所有平台的安装(编译过程)。能够输出各种各样的makefile或者project文件。Cmake 并不直接建构出最终的软件，而是产生其他工具的脚本（如Makefile ），然后再依这个工具的构建方式使用。
  CMake是一个比make更高级的编译配置工具，它可以根据不同平台、不同的编译器，生成相应的Makefile或者vcproj项目。从而达到跨平台的目的。Android Studio利用 CMake生成的是ninja，ninja是一个小型的关注速度的构建系统。我们不需要关心ninja的脚本，知道怎么配置cmake就可以了。从而可以看出cmake其实是一个跨平台的支持产出各种不同的构建脚本的一个工具。
  CMake的脚本名默认是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.

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.
#             native-lib
#             # Sets the library as a shared library.
#             SHARED
#             # Provides a relative path to your source file(s).
#        jni/native-lib.cpp)


# 添加jni库
add_library(
        ExJNI
        SHARED
        jni/ExJNI.cpp)


add_library(
        Log
        SHARED
        jni/Log.cpp)

include_directories(${CMAKE_SOURCE_DIR}/base/)

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

在Java代码中如何使用ExJNI.cpp库

/**
 * 静态注册  jni
 */
public class ExJNI {
    
    static {
        System.loadLibrary("ExJNI");
    }

    public native void takePhoto(Context context);
    public native void recordVideo(Context context);
    /**
     * 跳转页面
     */
    private void toActivity(Context context,Class c){
        context.startActivity(new Intent(context,c));
    }
}

在activity中实例化ExJNI ，调用两个jni底层原生方法实现跳转页面到拍照和录制视频
ExJNI ex = new ExJNI ();
ex.takePhoto(this) // 拍照
ex.recordVideo(this) // 录制视频

ExJNI.cpp库代码

//
// Created by Administrator on 2021/10/29.
//
#include <jni.h>
#include <string>
#include <pthread.h>
#include <Log.h>


#define takePhotoActivity "org/yxjme/exjni_two/a/TakePhotoActivity"
#define recordVideoActivity "org/yxjme/exjni_two/a/RecordVideoActivity"



extern "C" JNIEXPORT jstring JNICALL
Java_org_yxjme_exjni_1two_ExJNI_getMessage(JNIEnv * env,jobject thiz){
    std::string hh = "000000000000000000000000000";
    LOGI("[getMessage]->",env->NewStringUTF(hh.c_str()));
    /**
     * 获取类
     */
    jclass _jclass = env->GetObjectClass(thiz);
    /**
     * 获取函数id
     */
    jmethodID _MethodID = env->GetMethodID(_jclass, "showFiled", "(Ljava/lang/String;)V");
    /**
     * 传递进去的参数
     */
    jstring  resultMsgStr  = env->NewStringUTF("this is Success");
    /**
     * 调用函数
     */
    env->CallVoidMethod(thiz,_MethodID,resultMsgStr) ;
    return env->NewStringUTF(hh.c_str());
}


extern "C"
JNIEXPORT jobject JNICALL
Java_org_yxjme_exjni_1two_ExJNI_GetOBJ(JNIEnv *env, jobject thiz, jstring jstr) {

    jclass _jclass =  env->FindClass("org/yxjme/exjni_two/ExJNI") ;
    /**
     * 获取Java类的构造方法
     */
    jmethodID mId = env->GetMethodID(_jclass, "<init>", "(Ljava/lang/String;)V");
    /**
     *
     */
    jobject obj = env->NewObject(_jclass, mId,jstr);
    return obj;
}



extern "C"
JNIEXPORT jint JNICALL
Java_org_yxjme_exjni_1two_ExJNI_arrayLength(JNIEnv *env,
        jobject thiz,
        jintArray array_list) {

    int len = env ->GetArrayLength(array_list) ;
    LOGI("len = ",len);

    jclass  cls = env->FindClass("org/yxjme/exjni_two/ExJNI");
    jmethodID mID = env->GetMethodID(cls, "fun", "(I)Ljava/lang/String;");
    env->CallObjectMethod(thiz,mID,10000) ;
    return len ;
}


extern "C"
JNIEXPORT void JNICALL
Java_org_yxjme_exjni_1two_ExJNI_createThread(JNIEnv *env, jobject thiz) {

}



void * printHelloThread(void *){
    LOGI("hello thread");
    return nullptr;
}

/**
 * 定义结构体
 */
struct threadArgs{
    int code ;
    const char *result ;
};


void toActivityMethod(JNIEnv *pEnv, jobject pJobject, jobject pJobject1, const char string[1]);

/**
 * 打印传进的数据
 * @param arg
 * @return
 */
void * threadArgsBean(void *arg){
    threadArgs * args = static_cast<threadArgs *>(arg) ;
    LOGI("this is code %d",args->code);
    LOGI("this is result %s",args->result);
    return nullptr ;
}



extern "C"
JNIEXPORT void JNICALL
Java_org_yxjme_exjni_1two_ExJNI_createJNIThread(JNIEnv *env, jobject thiz) {
    /*句柄*/
    pthread_t handle;
    threadArgs *thread = new threadArgs ;
    thread->code = 0 ;
    thread->result = "传递成功";
    /*创建线程*/
    int ret = pthread_create(&handle,nullptr,printHelloThread,threadArgsBean(thread))  ;
    if(ret == 0 ){
        LOGD("create thread success") ;
    }else{
        LOGD("create thread failed") ;
    }
}



extern "C"
JNIEXPORT void JNICALL
Java_org_yxjme_exjni_1two_ExJNI_takePhoto(JNIEnv *env, jobject thiz,jobject obj) {
    toActivityMethod(env,thiz,obj,takePhotoActivity);
}


extern "C"
JNIEXPORT void JNICALL
Java_org_yxjme_exjni_1two_ExJNI_recordVideo(JNIEnv *env, jobject t,jobject obj) {
    toActivityMethod(env,t,obj,recordVideoActivity);
}



/**
 * 公共方法
 *
 * @param pEnv
 * @param pJobject
 * @param pJobject1
 * @param str
 */
void toActivityMethod(JNIEnv *pEnv, jobject pJobject, jobject pJobject1, const char str[1]) {
    jclass  c = pEnv->FindClass("org/yxjme/exjni_two/ExJNI");
    jmethodID mId = pEnv->GetMethodID(c, "toActivity","(Landroid/content/Context;Ljava/lang/Class;)V");
    jclass  _jcls = pEnv->FindClass(str);
    pEnv->CallVoidMethod(pJobject,mId,pJobject1,_jcls) ;
}

使用反射机制跳转activity界面

   /**
     * 使用反射实现跳转
     */
    private void toRecord() {
        Class<? extends ExJNI> cls = exJNI.getClass();
        try {

            ExJNI obj = cls.newInstance();
            /*获取需要反射的方法*/
            Method m = cls.getDeclaredMethod(
                    "toActivity", Context.class, Class.class);
            /*反射私有方法必须添加此方法才可调用*/
            m.setAccessible(true);
            /*开始调用该方法*/
            m.invoke(exJNI, MainActivity.this, RecordVideoActivity.class);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        }