用鸿蒙开发AI应用（八）JS框架访问内核层

目录：
前言
JS应用开发框架原理
内置模块
实现ace模块
开发界面程序

前言
上回说到，用C++来写UI界面的开发效率不如JS+HTML来的高，但设备开发又免不了要通过内核态来操作硬件，这里我们就要先打通从JS框架到设备驱动之间的联系。本章基于HDF驱动和JS+CSS+HTML的技术上进行，相关内容可以回顾用鸿蒙开发AI应用（五）HDF 驱动补光灯和用鸿蒙开发AI应用（六）UI篇这两篇。
 

JS应用开发框架原理
在第六篇里，我们已经体验了一下使用JS开发界面的流程，这里简单分析ace的实现原理。

先看框架图，类小程序的Web应用先编译成js bundle包，通过JS Data binding来获取对象映射。其中Observer实现了一个极简的MVVC模型，用于将DOM上的对象分为4种类型（render、data、styleSheet、function），采用数据劫持机制分别挂载到观察者的原型函数上，并转化到C++函数执行。

查看源码就会发现，JS的部分是极简的，JS 引擎采用了JerryScript，每一个标签对应了一个C++的Component类。绝大部分功能实际都由C++实现，包括事件注册和触发，页面路由，控件的更新，超时，文件操作，命令行输出等等... 所有API的100%对接不禁让我想起了一个动画片。

进入C++领域后就方便很多了，此时的ACE仍处于用户态，用HDF上的消息机制就能触达内核，无非是再包装一层API的套娃操作。

内置模块
这里有一系列@system.xxx的模块提供了访问APP、Router、Audio、Sensor等等的设备能力。ohos_module_config.h定义了JS框架中模块的别名到模块初始化函数的对应关系。其中app，dfx，router模块是必有的。

// Config information for built-in JS modules of OHOS platform
const Module OHOS_MODULES[] = {
#ifdef ENABLE_MODULE_REQUIRE_TEST
    {"sample", InitSampleModule},
#endif
    {"app", InitAppModule},
#ifdef FEATURE_MODULE_AUDIO
    {"audio", InitAudioModule},
#endif // FEATURE_MODULE_AUDIO
    {"dfx", InitDfxModule},
    {"router", InitRouterModule},
#ifdef ENABLE_MODULE_CIPHER
    {"cipher", InitCipherModule},
#endif
};

实现ace模块
背景知识介绍完了，就可以根据业务的复杂度来依葫芦画瓢的自定义ace模块封装功能，这里为了简化操作，我们直接在内置的app模块上挂载操作。

1. 定义头文件
修改foundation/ace/frameworks/lite/src/core/modules/app_module.h，加入ToggleLed函数并初始化。

namespace OHOS {
namespace ACELite {
class AppModule final : public MemoryHeap {
public:
    static JSIValue ToggleLed(const JSIValue thisVal, const JSIValue* args, uint8_t argsNum);

void InitAppModule(JSIValue exports)
{
    JSI::SetModuleAPI(exports, "getInfo", AppModule::GetInfo);
    JSI::SetModuleAPI(exports, "terminate", AppModule::Terminate);
    JSI::SetModuleAPI(exports, "toggleLed", AppModule::ToggleLed);
}
} // namespace ACELite
} // namespace OHOS
#endif // OHOS_ACELITE_APP_MODULE_H

2. 调用HDF驱动
在foundation/ace/frameworks/lite/src/core/modules/app_module.cpp中加入，

#include <fcntl.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include "hdf_sbuf.h"
#include "hdf_io_service_if.h"

#define LED_WRITE_READ 1
#define LED_SERVICE "led_service"

JSIValue AppModule::ToggleLed(const JSIValue thisVal, const JSIValue *args, uint8_t argsNum)
{
    HILOG_ERROR(HILOG_MODULE_ACE, "led button pressed.");
    printf("led button pressed
");

    struct HdfIoService *serv = HdfIoServiceBind(LED_SERVICE, 0);
    if (serv == NULL)
    {
        printf("fail to get service %s
", LED_SERVICE);
        return JSI::CreateUndefined();
    }

    static struct HdfDevEventlistener listener = {
        .callBack = OnDevEventReceived,c
        .priv = (void *)"Service0"};

    if (HdfDeviceRegisterEventListener(serv, &listener) != HDF_SUCCESS)
    {
        printf("fail to register event listener
");
        return JSI::CreateUndefined();
    }

    const char *send_cmd = "toggle LED";

    if (SendEvent(serv, send_cmd))
    {
        printf("fail to send event
");
        return JSI::CreateUndefined();
    }

    if (HdfDeviceUnregisterEventListener(serv, &listener))
    {
        printf("fail to  unregister listener
");
        return JSI::CreateUndefined();
    }

    HdfIoServiceRecycle(serv);

    return JSI::CreateUndefined();
}

3. 配置HDF头文件路径
修改 foundation/ace/frameworks/lite/src/core/modules/BUILD.gn

include_dirs = [
    "presets",
    "maplejs",
    "//test/lite/testservice/include",
    "//vendor/huawei/watchgt/devkit/hal/include",
	"//foundation/distributedschedule/interfaces/innerkits/samgr_lite/communication/mpc/transport",
    "//foundation/distributedschedule/interfaces/innerkits/samgr_lite/communication/mpc",
    
    "//drivers/hdf/lite/include/host",
    "$HDF_FRAMEWORKS/ability/sbuf/include",        
    "$HDF_FRAMEWORKS/core/shared/include",
    "$HDF_FRAMEWORKS/core/host/include",
    "$HDF_FRAMEWORKS/core/master/include",
    "$HDF_FRAMEWORKS/include/core",
    "$HDF_FRAMEWORKS/include/utils",
    "$HDF_FRAMEWORKS/utils/include",
    "$HDF_FRAMEWORKS/include/osal",
    "$HDF_FRAMEWORKS/adapter/syscall/include",
    "$HDF_FRAMEWORKS/adapter/vnode/include",
]

修改foundation/ace/frameworks/lite/BUILD.gn

config("ace_lite_config") {
  include_dirs = [
  ...
  ]
  
  include_dirs += [
    "//drivers/hdf/lite/include/host",
    "$HDF_FRAMEWORKS/ability/sbuf/include",        
    "$HDF_FRAMEWORKS/core/shared/include",
    "$HDF_FRAMEWORKS/core/host/include",
    "$HDF_FRAMEWORKS/core/master/include",
    "$HDF_FRAMEWORKS/include/core",
    "$HDF_FRAMEWORKS/include/utils",
    "$HDF_FRAMEWORKS/utils/include",
    "$HDF_FRAMEWORKS/include/osal",
    "$HDF_FRAMEWORKS/adapter/syscall/include",
    "$HDF_FRAMEWORKS/adapter/vnode/include",
  ]
}
shared_library("ace_lite") {
      
  public_deps = [
    "//base/security/frameworks/crypto_lite/js/builtin:ace_kit_cipher",
    "//foundation/graphic/lite/frameworks/surface:surface",
    "//foundation/multimedia/frameworks/camera_lite:camera",
    "//foundation/multimedia/frameworks/player_lite:player",
    "//foundation/multimedia/interfaces/kits/player_lite/js/builtin:audio_api",
    "//third_party/bounds_checking_function:libsec_shared",
    "//third_party/cJSON:cjson_shared",
    "//third_party/jerryscript/jerry-core:jerry-core_shared",
    "//third_party/jerryscript/jerry-ext:jerry-ext_shared",
    "//third_party/jerryscript/jerry-libm:jerry-libm_shared",
    "//third_party/jerryscript/jerry-port/default:jerry-port-default_shared",
    "//utils/native/lite/js/builtin:ace_utils_kits",
    "//utils/native/lite/timer_task:ace_kit_timer",

    "//drivers/hdf/lite/manager:hdf_core",
    "//drivers/hdf/lite/adapter/osal/posix:hdf_posix_osal",
  ]
}

4. 编译烧录

python build.py my_hi3516dv300 -b debug

涉及到HDF驱动和ACE框架，就要重新完整烧录镜像文件。

开发界面程序
1. 配置模块接口
前面我们在内置app模块上增加了函数taggleLed，对于DevEco Studio来说是无法直接获取的，所以要先增加api接口。

修改HuaweiSdkjs2.0.1.93apismartVision@system.app.d.ts文件

export default class App {
  /**
   * Obtains the declared information in the config.json file of an application.
   */
  static getInfo(): IAppInfo;

  /**
   * Destroys the current ability.
   */
  static terminate(): void;
  
  /**
   * 翻转Led
   */
  static toggleLed(): void;
}

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作者：bluishfish

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