一、开发环境

系统版本：OpenHarmony 4.0.10.13
设备平台：rk3568
SDK版本：fullSDK 4.0.10.13
DevEco Studio版本：4.1.0.400

二、需求背景

定制OpenHarmony 系统组合按键功能，例如仿Android Power + VOL_Up组合键实现截屏功能

三、需求分析

查询OpenHarmony API接口文档，存在组合按键订阅模块，用于处理组合按键的订阅
@ohos.multimodalInput.inputConsumer (组合按键)(系统接口)

let leftAltKey = 2045;
let tabKey = 2049;
let keyOptions: inputConsumer.KeyOptions = {
  preKeys: [ leftAltKey ],
  finalKey: tabKey,
  isFinalKeyDown: true,
  finalKeyDownDuration: 0
};
let callback = (keyOptions: inputConsumer.KeyOptions) => {
  console.log(`keyOptions: ${JSON.stringify(keyOptions)}`);
}
try {
  inputConsumer.on("key", keyOptions, callback);
} catch (error) {
  console.log(`Subscribe failed, error: ${JSON.stringify(error, [`code`, `message`])}`);
}

通过此接口可订阅特定的组合按键，触发特定事件，包括但不限于：

A + B ==>截屏/打开设置/打开网页/进入Launcher等等

为了更好的管理和分发系统全局组合按键事件，可通过创建一个系统服务应用，开机运行后在后台注册相关的组合按键。
本文首先介绍如何创建一个系统服务应用。

四、实现过程

创建工程

打开DevEco Studio
File > New > Create Project > Application >[OpenHarmony]Empty Ability > Next

确认应用工程名、包名、SDK版本、Model > Next

创建ServiceExtensionAbility

可参考：创建ServiceExtensionAbility
在工程entry/src/main/ets目录创建services目录，用于存放自定义ServiceExtensionAbility

ets > 鼠标右键 > New > Directory > services

在新创建的services中创建自定义ServiceExtensionAbility
services > 鼠标右键 > New > ArkTs File > ServiceExtAbility

ServiceExtAbility.ets内容为：

import ServiceExtensionAbility from '@ohos.app.ability.ServiceExtensionAbility';
import Want from '@ohos.app.ability.Want';
import hilog from '@ohos.hilog';
import rpc from '@ohos.rpc';

const TAG: string = '[ServiceExtAbility]';
const DOMAIN_NUMBER: number = 0xFF00;

class ServiceStub extends rpc.RemoteObject {
  constructor(des: string) {
    super(des);
  }
}

export default class ServiceExtAbility extends ServiceExtensionAbility {

  onCreate(want: Want): void {
    let serviceExtensionContext = this.context;
    hilog.info(DOMAIN_NUMBER, TAG, `onCreate, want: ${want.abilityName}`);
  };

  onRequest(want: Want, startId: number): void {
    hilog.info(DOMAIN_NUMBER, TAG, `onRequest, want: ${want.abilityName}`);
  };

  onConnect(want: Want): rpc.RemoteObject {
    hilog.info(DOMAIN_NUMBER, TAG, `onConnect, want: ${want.abilityName}`);
    // 返回ServiceExtImpl对象，客户端获取后便可以与ServiceExtensionAbility进行通信
    return new ServiceStub('ServiceExtAbilityService');
  };

  onDisconnect(want: Want): void {
    hilog.info(DOMAIN_NUMBER, TAG, `onDisconnect, want: ${want.abilityName}`);
  };

  onDestroy(): void {
    hilog.info(DOMAIN_NUMBER, TAG, 'onDestroy');
  };
};

注册ServiceExtensionAbility

在工程Module对应的module.json5配置文件中

• 注册ServiceExtensionAbility
• type标签需要设置为“service”
• srcEntry标签表示当前ExtensionAbility组件所对应的代码路径。
• mianElement设置为ServiceExtAbility
  module.json5文件内容如下：

{
  "module": {
    "name": "entry",
    "type": "entry",
    "description": "$string:module_desc",
    "mainElement": "ServiceExtAbility",
    "deviceTypes": [
      "default",
      "tablet"
    ],
    "deliveryWithInstall": true,
    "installationFree": false,
    "pages": "$profile:main_pages",
    "abilities": [
      {
        "name": "EntryAbility",
        "srcEntry": "./ets/entryability/EntryAbility.ets",
        "description": "$string:EntryAbility_desc",
        "icon": "$media:icon",
        "label": "$string:EntryAbility_label",
        "startWindowIcon": "$media:startIcon",
        "startWindowBackground": "$color:start_window_background",
        "exported": true,
        "skills": [
          {
            "entities": [
              "entity.system.home"
            ],
            "actions": [
              "action.system.home"
            ]
          }
        ]
      }
    ],
    "extensionAbilities": [
      {
        "name": "ServiceExtAbility",
        "icon": "$media:icon",
        "label": "$string:EntryAbility_label",
        "description": "service",
        "type": "service",
        "exported": true,
        "srcEntry": "./ets/services/ServiceExtAbility.ets"
      }
    ]
  }
}

构建和安装hap

对应用进行自动签名
File > Project Structure… > Project > Signing Configs > Automatically generate signature

获取应用签名指纹

#打开设备debug log
hdc shell param set persist.sys.hilog.debug.on true
hdc shell param set hilog.debug.on true 
hdc shell  hilog -b D

# 过滤安装hap时的finger信息
hdc shell "hilog |grep finger"

点击DevEco Studio 运行按钮，IDE会自动编译和安装hap包

不出预料会安装失败，但hilog中会看到指纹信息,即
42BBCECD7084D3C605F9FAF53E61278DAC8D944175ADABBB49B507B09774F490

hdc shell "hilog |grep finger"
08-05 23:44:23.357   547 24958 D C02f00/HapVerify: GenerateFingerprint: fingerprint is : 42BBCECD7084D3C605F9FAF53E61278DAC8D944175ADABBB49B507B09774F490

配置特权文件install_list_capability.json

# 从设备导出配置文件
hdc shell mount -o remount,rw /
hdc file recv /system/etc/app/install_list_capability.json  C:\Users\xxx\Desktop

在install_list_capability.json 末尾配置

		...
		},
        {
            "bundleName": "com.example.myapplication",
            "app_signature" : ["42BBCECD7084D3C605F9FAF53E61278DAC8D944175ADABBB49B507B09774F490"],
            "allowAppUsePrivilegeExtension": true,
            "allowAppDesktopIconHide": true,
            "singleton": true,
            "keepAlive": true
        }

替换install_list_capability.json并重启

hdc shell mount -o remount,rw /
hdc file send C:\Users\xxx\Desktop\\install_list_capability.json /system/etc/app/install_list_capability.json

构建hap包

由于上面配置了应用为singleton安装hap包，仍无法直接用IDE安卓，需将hap包推至设备通过bm命令安装
Build > Build Hap(s)/APP(s) > Build Hap(s)
编译完成后得到：entry/build/default/outputs/default/entry-default-signed.hap

# 将hap push至设备/data目录
hdc file send D:\projects\DevEcoProjects\MyApplication\entry\build\default\outputs\default\entry-default-signed.hap /data

#bm安装hap
hdc shell bm install -p /data/entry-default-signed.hap -u 0

#重启设备
hdc shell reboot

校验

重启后可在IDE 看到demo的日志

也可在设备进程中看到service被拉起

ps -A | grep myapplication

总结

通过本文你已经学会如何创建开机自启后台服务，后续将在此服务中订阅组合按键，实现截屏、打开设置功能
OpenHarmony定制系统组合按键（二）