NAPI篇【4】——NAPI应用点亮一个LED

OpenHarmony的NAPI功能为开发者提供了JS与C/C++不同语言模块之间的相互访问，交互的能力，使得开发者使用C或者C++语言实现应用的关键功能。如操作开发板中某个GPIO节点的状态（OpenHarmony并没有提供直接操作GPIO口状态的API），点亮一个LED灯。

本篇基于前3篇NAPI的讲解总结，做一个控制开发板上LED灯状态的应用作为完结篇。

一、环境准备

设备：rk3568开发板

开发环境：DevEco Studio4.0.0.600

二、NAPI函数编写

1、基于NAPI的GPIO节点控制函数

OpenHarmony并没有提供直接操作GPIO口状态的API。若需要控制开发板上LED灯的亮灭，需要通过NAPI的方式，写一个可以查询GPIO口状态、一个可以对节点写1和一个可以对节点写0的函数。

（1）main目录如下：

（2）bq_function.cpp

#include "napi/native_api.h"
#include "napi/native_api.h"
#include <cstring>
#include <js_native_api.h>
#include <sys/un.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>using namespace std;
//对指定节点写1
static napi_value Bq_GPIO_On(napi_env env, napi_callback_info info) {size_t argc = 1;napi_value args[1] = {nullptr};napi_get_cb_info(env, info, &argc, args, nullptr, nullptr);napi_valuetype valuetype0;napi_typeof(env, args[0], &valuetype0);char *ledPath = new char[150]{};size_t buffSize = 100;size_t realSize = 0;napi_get_value_string_utf8(env, args[0], ledPath, buffSize, &realSize);int fd;char *ret = new char[50]{};fd = open(ledPath, O_RDWR | O_TRUNC | O_NOCTTY);if (fd < 0) {strcpy(ret, "fail to open file");} else {strcpy(ret, "1");write(fd, "1", 1);close(fd);}napi_value returnValue = nullptr;napi_create_string_utf8(env, ret, strlen(ret), &returnValue);return returnValue;
}//对指定节点写0
static napi_value Bq_GPIO_Off(napi_env env, napi_callback_info info) {size_t argc = 1;napi_value args[1] = {nullptr};napi_get_cb_info(env, info, &argc, args, nullptr, nullptr);napi_valuetype valuetype0;napi_typeof(env, args[0], &valuetype0);char *ledPath = new char[150]{};size_t buffSize = 100;size_t realSize = 0;napi_get_value_string_utf8(env, args[0], ledPath, buffSize, &realSize);int fd;char *ret = new char[50]{};fd = open(ledPath, O_RDWR | O_TRUNC | O_NOCTTY);if (fd < 0) {strcpy(ret, "fail to open file");} else {strcpy(ret, "0");write(fd, "0", 1);close(fd);}napi_value returnValue = nullptr;napi_create_string_utf8(env, ret, strlen(ret), &returnValue);return returnValue;
}//查询指定节点状态
static napi_value bq_GPIO_State(napi_env env, napi_callback_info info) {size_t argc = 1;napi_value args[1] = {nullptr};napi_get_cb_info(env, info, &argc, args, nullptr, nullptr);napi_valuetype valuetype0;napi_typeof(env, args[0], &valuetype0);char *ledPath = new char[150]{};size_t buffSize = 100;size_t realSize = 0;napi_get_value_string_utf8(env, args[0], ledPath, buffSize, &realSize);char *ret = new char[50]{};FILE *fp;char gpioValuePath[200];char gpioValue[2];// 构建GPIO口值文件路径snprintf(gpioValuePath, sizeof(gpioValuePath), "%s", ledPath);if (access(gpioValuePath, F_OK) == -1) {strcpy(ret, "Error: the GPIO is not exist");napi_value returnValue = nullptr;napi_create_string_utf8(env, ret, strlen(ret), &returnValue);return returnValue;}// 打开GPIO口值文件fp = fopen(gpioValuePath, "r");if (fp == NULL) {perror("Error opening GPIO value file");strcpy(ret, "Error opening GPIO value file");} else {// 读取GPIO口值if (fgets(gpioValue, sizeof(gpioValue), fp) == NULL) {perror("Error reading GPIO value");fclose(fp);strcpy(ret, "Error reading GPIO value");} else {strcpy(ret, gpioValue);}}fclose(fp);napi_value returnValue = nullptr;napi_create_string_utf8(env, ret, strlen(ret), &returnValue);return returnValue;
}EXTERN_C_START static napi_value Init(napi_env env, napi_value exports) {napi_property_descriptor desc[] = {{"bq_GPIO_On", nullptr, Bq_GPIO_On, nullptr, nullptr, nullptr, napi_default, nullptr},{"bq_GPIO_Off", nullptr, Bq_GPIO_Off, nullptr, nullptr, nullptr, napi_default, nullptr},{"bq_GPIO_State", nullptr, bq_GPIO_State, nullptr, nullptr, nullptr, napi_default, nullptr}};napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);return exports;
}
EXTERN_C_ENDstatic napi_module demoModule = {.nm_version = 1,.nm_flags = 0,.nm_filename = nullptr,.nm_register_func = Init,.nm_modname = "entry",.nm_priv = ((void *)0),.reserved = {0},
};extern "C" __attribute__((constructor)) void RegisterEntryModule(void) { napi_module_register(&demoModule); }

2、NAPI函数与导出与配置

（1）index.d.ts

export const bq_GPIO_On: (ledPath: string) =>  Promise<string>;//节点写1export const bq_GPIO_Off: (ledPath: string) =>  Promise<string>;//节点写0export const bq_GPIO_State: (ledPath: string) => Promise<string>;//节点状态查询

（2）CMakeLists.txt

# the minimum version of CMake.
cmake_minimum_required(VERSION 3.4.1)
project(Demo_Led)set(NATIVERENDER_ROOT_PATH ${CMAKE_CURRENT_SOURCE_DIR})include_directories(${NATIVERENDER_ROOT_PATH}${NATIVERENDER_ROOT_PATH}/include)add_library(entry SHARED bq_func.cpp)
target_link_libraries(entry PUBLIC libace_napi.z.so)

（3）build-profile.json5

（4）oh-package.json5

三、Openharmony UI交互界面编写

1、UI界面编写，NAPI函数引用

（1）index.ets

开发板控制LED灯节点地址为：/sys/class/leds/pilot_lamp/brightness

import NAPI from 'libentry.so';//引出NAPI接口
import promptAction from '@ohos.promptAction';
@Observed
class ledModel {public ledName: string //LED灯名称public ledAddress: string //LED灯的节点地址public ledState: boolean //LED灯状态public isLedExit: boolean //LED灯节点是否存在public ledStateCheck: string //检测返回值constructor(LedName: string, LedAddress: string, LedState: boolean = false, isLedExit: boolean = true, LedStateCheck: string = '') {this.ledName = LedNamethis.ledAddress = LedAddressthis.ledState = LedStatethis.isLedExit = isLedExitthis.ledStateCheck = LedStateCheck}
}
@Entry
@Component
struct Index {@State message: number = 0;@State led: ledModel = new ledModel('LED_Green','/sys/class/leds/pilot_lamp/brightness')//开发板控制LED灯节点地址'/sys/class/leds/pilot_lamp/brightness'private setIntervalID: number = -1async ledCheck() {this.led.ledStateCheck = await NAPI.bq_GPIO_State(this.led.ledAddress)if (this.led.ledStateCheck === '1') {this.led.ledState = true} else if (this.led.ledStateCheck === 'Error: the GPIO is not exist') {this.led.isLedExit = false} else {this.led.ledState = false}}async aboutToAppear() {await this.ledCheck()//状态扫描this.setIntervalID = setInterval(async () => {await this.ledCheck()}, 500)}aboutToDisappear() {clearInterval(this.setIntervalID)}build() {Column() {Text("点亮一个LED灯").size({ width: '100%', height: 35 }).margin({ top: 10, bottom: 10 }).textAlign(TextAlign.Center).fontSize(30).fontWeight(800)Column({ space: 10 }) {ledList({ item: this.led})}.margin({ top: 20, bottom: 10 }).size({ width: '50%', height: 50 }).justifyContent(FlexAlign.Start).alignSelf(ItemAlign.Center)}.justifyContent(FlexAlign.Center).alignItems(HorizontalAlign.Center).size({ width: '100%', height: '100%' })}
}
@Component
struct ledList {@ObjectLink item: ledModeltip(str: string) {let show: stringswitch (str) {case "1":show = '已打开';break;case "0":show = '已关闭';break;default:show = `error: ${str}`}promptAction.showToast({message: show,duration: 800})}build() {Row() {Text(`${this.item.ledName}`).size({ width: '70%', height: 35 }).fontSize(30).fontWeight(700).fontColor(this.item.isLedExit === true ? Color.Black : '#c9c9cd')Blank()Toggle({ type: ToggleType.Switch, isOn: this.item.ledState }).size({ width: 80, height: 35 }).enabled(this.item.isLedExit).onChange(async (isOn) => {if (isOn) {let res: string = await NAPI.bq_GPIO_On(this.item.ledAddress)this.tip(res)} else {let res: string = await NAPI.bq_GPIO_Off(this.item.ledAddress)this.tip(res)}})}.width('100%')}
}