使用JNI和反射实现调用Java方法跳转页面

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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(ExJNISHAREDjni/ExJNI.cpp)add_library(LogSHAREDjni/Log.cpp)include_directories(${CMAKE_SOURCE_DIR}/base/)# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.find_library( # Sets the name of the path variable.log-lib# Specifies the name of the NDK library that# you want CMake to locate.log )# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.target_link_libraries( # Specifies the target library.
#                       native-libExJNILog# Links the target library to the log library# included in the NDK.${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();}