JNI开发：cpp与java通信

java

MainActivity.java

package com.example.administrator.myapplication; import android.os.Bundle; import androidx.appcompat.app.AppCompatActivity; import android.util.Log; import android.view.Surface; import android.view.SurfaceView; import android.view.View; import android.widget.Button; public class MainActivity extends AppCompatActivity { static { System.loadLibrary("demo"); } private Button conn_and_start; // cpp方法 private native int Start(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); initView(); initViewListener(); } private void initViewListener() { // TODO Auto-generated method stub btn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub Start(); } }); } private void initView() { btn = (Button) findViewById(R.id.btn); } public void callBack(String p_result) { Log.e("callBack", "callBack: "+p_result); } }

cpp

demo.cpp

#include"demo.h" #include"staticJNI.h" #include <jni.h> #include <android/log.h> #define LOG_TAG "GLRender" #define LOGI(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__) #define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__) #ifdef __cplusplus extern "C" { #endif void detect_face_cb(char* p_result) { if (p_result != NULL) { char *picInfo = p_result; JNIEnv *env = NULL; JavaVM *javaVm = staticJNI::getJavaVM(); if (javaVm == NULL) return; int nStatus = (javaVm)->GetEnv((void **) &env, JNI_VERSION_1_4); if (nStatus != JNI_OK) { nStatus = (javaVm)->AttachCurrentThread(&env, NULL); } if (nStatus != JNI_OK) { return; } jclass clazz = staticJNI::getMainActivity_cls(); if (clazz != NULL) { jobject obj = env->AllocObject(clazz); jmethodID mid = env->GetMethodID(clazz, "callBack","(Ljava/lang/String;)V"); if (picInfo != NULL) env->CallVoidMethod(obj, mid,env->NewStringUTF(picInfo)); } } } jint Java_com_example_administrator_myapplication_MainActivity_Start(JNIEnv *env, jobject obj) { char * c_result = "callBack"; detect_face_cb(c_result); return 0; } #ifdef __cplusplus } #endif

staticJNI.h

#ifndef _STATICJNI_H_ #define _STATICJNI_H_ #include <jni.h> #ifdef __cplusplus extern "C" { #endif static JavaVM *javaVm; static jclass main_cls; class staticJNI { public: static JavaVM* getJavaVM(); static jclass getMainActivity_cls(); }; #ifdef __cplusplus } #endif #endif

staticJNI.cpp

#ifdef ANDROID #include "staticJNI.h" #include <stdlib.h> #include <android/log.h> #define LOG_TAG "staticJNIJava" #define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__) #define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__) #define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__) JavaVM* staticJNI::getJavaVM() { return javaVm; } jclass staticJNI::getMainActivity_cls() { return main_cls; } jint JNI_OnLoad(JavaVM* vm, void* reserved) { JNIEnv *env; javaVm = vm; int nRet = -1; if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) == JNI_OK) { if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) == JNI_OK) { jclass main_clazz = env->FindClass("com/example/administrator/myapplication/MainActivity"); if(main_clazz != NULL) { main_cls = (jclass)env->NewGlobalRef(main_clazz); nRet = JNI_VERSION_1_4; } } nRet = JNI_VERSION_1_4; } return nRet; } void JNI_OnUnload(JavaVM* vm, void* reserved) { javaVm = NULL; int nRet = -1; } #endif