Android JNI 在C++多线程调用Java的回调函数

java 复制代码

public interface Callback {
    void onResult(int status, String message);
}

java 复制代码

public class Sample {
    static {
        System.loadLibrary("sample_core_jni");
    }

    public static native int process(long handle, String message);


    public static void onCallback(int status, String message) {
        if (mCallback != null) {
            mCallback.onResult(status, message);
        }
    }

    private static Callback mCallback;

    public static void setCallback(Callback callback) {
        if (callback == null) {
            throw new NullPointerException("callback can not be null");
        }
        mCallback = callback;
    }

// 添加其他native函数
....
}

cpp 复制代码

#include <jni.h>
#include <iostream>
 
// 全局引用，确保JNI环境可以访问
JavaVM *g_VM;
jclass gCallbackClassSample = nullptr;
jmethodID gOnCallbackMethodID = nullptr;


JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
    JNIEnv *env = nullptr;
    jint result = -1;
    if (vm->GetEnv((void **) &env, JNI_VERSION_1_6) != JNI_OK) {
        return result;
    }

    //JavaVM是虚拟机在JNI中的表示，等下再其他线程回调java层需要用到
    env->GetJavaVM(&g_VM);

    register_fields(env);

    LOGI("JNI OnLoad result : %d", result);
    return JNI_VERSION_1_6;
}

register_fields(JNIEnv *env) {

//注册Java回调函数所在的类及回调函数
}



int ChatCallback(int status, const char *output) {
    JNIEnv *env;
    bool mNeedDetach = false;
    //获取当前native线程是否有没有被附加到jvm环境中
    int getEnvStat = (*g_VM).GetEnv( (void **)&env, JNI_VERSION_1_6);
    if (getEnvStat == JNI_EDETACHED) {
        //如果没有， 主动附加到jvm环境中，获取到env
        if (g_VM->AttachCurrentThread(&env, NULL) != JNI_OK) {
            LOGE("ChatCallback failed to attach current thread");
        }
        mNeedDetach = JNI_TRUE;
    }
    jString j_out = native_message_to_java_message(env, output);

    if (fields.chat_result_callback != nullptr) {
        env->CallStaticVoidMethod(gCallbackClassSample, gOnCallbackMethodID, (int)status, j_out);
    }
    //释放当前线程
    if(mNeedDetach) {
        g_VM->DetachCurrentThread();
    }
    env = NULL;

    return 0;
}

extern "C"
JNIEXPORT void JNICALL
Java_com_example_yourapp_process(JNIEnv *env, jlong handle, jString message) {

     //
     const char* c_message = ...
     //该函数为异步函数
     int err = Chat(handle, c_message, ChatCallback);
}