Android纯原生NativeActivity机制解析

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public class testgame extends Cocos2dxActivity {
        protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
        }

        public Cocos2dxGLSurfaceView onCreateView() {
                return new LuaGLSurfaceView(this);
        }

        static {
                System.loadLibrary("cocos2dlua");
        }
}

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typedef struct ANativeActivity {
    struct ANativeActivityCallbacks* callbacks;

    ......

} ANativeActivity;

typedef struct ANativeActivityCallbacks {
    /**
     * 当NativeActivity 启动时回调.  就像原来 JAVAActivity.onStart()一样
     */
    void (*onStart)(ANativeActivity* activity);

    //类似的还有
    void (*onResume)(ANativeActivity* activity);
    void* (*onSaveInstanceState)(ANativeActivity* activity, size_t* outSize);
    void (*onPause)(ANativeActivity* activity);
    void (*onStop)(ANativeActivity* activity);
    void (*onDestroy)(ANativeActivity* activity);

    ......

} ANativeActivityCallbacks;

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static void onStart(ANativeActivity* activity) {
    printf("hello world");
}

static void onDestroy(ANativeActivity* activity) {
    printf("bye...");
}

//实现入口点函数, 就像main一样
void ANativeActivity_onCreate(ANativeActivity* activity,void* savedState, size_t savedStateSize) {
    //实现设置回调函数
    activity->callbacks->onDestroy = onDestroy;
    activity->callbacks->onStart = onStart;
}

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//实现入口点回调函数
void ANativeActivity_onCreate(ANativeActivity* activity,
        void* savedState, size_t savedStateSize) {
    LOGV("Creating: %p\n", activity);

    //设置activity回调函数
    activity->callbacks->onDestroy = onDestroy;
    activity->callbacks->onStart = onStart;
    ......
    activity->callbacks->onInputQueueCreated = onInputQueueCreated;
    activity->callbacks->onInputQueueDestroyed = onInputQueueDestroyed;

    //生成android_app
    activity->instance = android_app_create(activity, savedState, savedStateSize);
}

static struct android_app* android_app_create(ANativeActivity* activity,
        void* savedState, size_t savedStateSize) {

    ......

    //声明事件管道
    android_app->msgread = msgpipe[0];
    android_app->msgwrite = msgpipe[1];

    //在新线程中让app_entry
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    pthread_create(&android_app->thread, &attr, android_app_entry, android_app);

    ......
}

static void* android_app_entry(void* param) {
    struct android_app* android_app = (struct android_app*)param;

    android_app->config = AConfiguration_new();
    AConfiguration_fromAssetManager(android_app->config, android_app->activity->assetManager);

    print_cur_config(android_app);

    //设置消息"循环器"来源
    android_app->cmdPollSource.id = LOOPER_ID_MAIN;
    android_app->cmdPollSource.app = android_app;
    //设置消息辅助类的事件处理回调
    android_app->cmdPollSource.process = process_cmd;

    /**
     *  这里使用了ALooper辅助类, 实现源码暂时找不到, 推测就是会监听刚才声明的`事件管道`的读取端
     *  当有消息来的时候就调用cmdPollSource.process指定的回调函数process_cmd
     */
    ALooper* looper = ALooper_prepare(ALOOPER_PREPARE_ALLOW_NON_CALLBACKS);
    ALooper_addFd(looper, android_app->msgread, LOOPER_ID_MAIN, ALOOPER_EVENT_INPUT, NULL,
            &android_app->cmdPollSource);
    android_app->looper = looper;

    //给个标志给主线程, 让主线程知道我们已经初始化完毕, 可以继续下一步了
    pthread_mutex_lock(&android_app->mutex);
    android_app->running = 1;
    pthread_cond_broadcast(&android_app->cond);
    pthread_mutex_unlock(&android_app->mutex);

    //调用app实现的android_main
    android_main(android_app);

    android_app_destroy(android_app);
    return NULL;
}

static void process_cmd(struct android_app* app, struct android_poll_source* source) {
    int8_t cmd = android_app_read_cmd(app);
    android_app_pre_exec_cmd(app, cmd);
    //调用app实现的onAppCmd
    if (app->onAppCmd != NULL) app->onAppCmd(app, cmd);
    android_app_post_exec_cmd(app, cmd);
}