system capability call: teach you step by step to play “system-level magic”

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hello!I am Xiao L, the female programmer who “digs and digs” in HarmonyOS Next code~ Today we will talk about system capability calls – this is like opening a “system backdoor” for the application, which can directly call Hongmeng’s “bottom superpowers”.Without further ado, just get some real information!



Chapter 1: System Ability: Hongmeng’s “Eighteen Martial Arts”



1. Core capabilities parade

HarmonyOS Next’s system abilities are like superhero groups, each with its own unique skills:

  1. Equipment Management Hero
  2. Skills: Real-time monitoring of CPU and memory usage, and can also manage the “work and rest” of the device (such as power saving mode).
  3. Scenario: When the application is stuck, it can tell you: “Brother, you account for 80% of the memory! It’s time to lose weight!”
  4. File System Captain
  5. Skills: Local files can be read and written casually, and files can be shared across devices, just like there is a “file portal”.
  6. Leng Knowledge: It has a dedicated “small room” (safety sandbox) for each application. Do other applications want to steal data?No way!
  7. Communication Superman
  8. Skills: Can connect to Wi-Fi, Bluetooth, NFC, and use distributed soft bus to make the device “hand in hand”.
  9. Famous scene: Mobile phones and car computers transmit navigation information in seconds through soft buses, which is faster than your object’s reply to messages~
  10. Sensor Elf
  11. Skill: Can sense temperature, light, acceleration, and even your heartbeat (if the device supports it).
  12. Usage of brains: Determine whether you are drunk or not according to the degree of shaking you walk, and automatically turn on the “anti-fall mode” ~



2. Why is this the “secret cheat” of developers?

Let me give you a chestnut:

  • In the past, when developing applications, such as decorating in a “unfinished house”, you had to do everything yourself;
  • Now with the system capabilities, it is like living in a “fine decoration room”, with all water, electricity and coal, just move in with your luggage!
    For example, to make a fitness app:
  • Use sensor capabilities to directly obtain motion data without connecting to hardware by yourself;
  • Use communication capabilities to synchronize data to the cloud in real time, without writing complex network protocols;
  • Optimize power consumption with equipment management capabilities, so that the APP can “save power and drive”.



Chapter 2: Document Management: The correct way to “deal with documents”



1. Reading files: as simple as dismantling express delivery

import fs from '@ohos.file.fs';

async function read file() 
    try 
// Opening a file is like unpacking a express delivery
const file = await fs.open('/data/test.txt', fs.OpenMode.READ_ONLY);
// Create an input stream and start "disconnecting express"
const input stream = await fs.createInputStream(file);
// Prepare the "Express Box" (buffer)
const buffer = new ArrayBuffer(1024);
// Reading data is like taking something from a courier box
const length = await input stream.read(buffer);
const data = new Uint8Array(buffer.slice(0, length));
console.log('File content:' + new TextDecoder().decode(data));
// Remember to "throwing the express box" (release resources)
await input stream.close();
await fs.close(file);
     catch (error) 
console.error('Read file overturns:' + error.message);
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Note: Don’t write the path incorrectly!Otherwise, it would be like the express delivery address is written wrongly and the file cannot be found ~



2. Write a file: “Write a love letter” to the file

import fs from '@ohos.file.fs';

async function write file() 
    try 
// Open the file and create it if it doesn’t exist (like buying a new notebook)
const file = await fs.open('/data/test.txt', fs.OpenMode.CREATE  catch (error) 
console.error('Failed to write file:' + error.message);
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Hearing joke: If the write fails, it may be that the file is “inflicting a temper” (no permissions), remember to give it a “Permissions Cake” ~



Chapter 3: Advanced Operation: Let the sensor and network “group CP”



1. Intelligent environment monitoring: Make the device “clear ears and bright eyes”

Imagine: your smart air conditioner can adjust the temperature by yourself and transmit data to your mobile phone – this is the “dream linkage” of sensor + network!



1. Step 1: Use sensors to “sensor the world”

import sensor from '@ohos.sensor';

function temperature measurement() 
const Temperature sensor = sensor.getDefaultSensor(sensor.SensorTypeId.TEMPERATURE);
if (temperature sensor) 
// Subscribe to temperature changes, just like monitoring the air conditioner remote control
Temperature sensor.subscribe((data) => 
console.log(`Current temperature: $data.temperature℃, a little $data.temperature > 26 ? 'hot' : 'cold'~`);
        );
     else 
console.log('The temperature sensor cannot be found, the device may have "cold"~');
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2. Step 2: Use the Internet to “transmit intelligence”

import http from '@ohos.net.http';

async function transfers data to the cloud (temperature: number) 
const request = http.createHttp();
const option = 
        method: http.RequestMethod.POST,
url: 'http://your cloud address/api/temp',
        headers:  'Content-Type': 'application/json' ,
        body: JSON.stringify( 
Device ID: 'SmartAirConditioner_001',
Temperature: Temperature,
Time: new Date().toISOString()
        )
    ;
    try 
const response = await request.request(option);
console.log('The cloud has received temperature information, reply:' + response.result);
     catch (error) 
console.error('Information delivery failed:' + error.message);
     finally 
Request.destroy(); // Destroy the request and save resources
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3. Step 3: Group CP!Let the data “move”

Temperature measurement(); // Start measuring temperature first
setInterval(async () => 
const Temperature sensor = sensor.getDefaultSensor(sensor.SensorTypeId.TEMPERATURE);
if (temperature sensor) 
const latest data = await temperature sensor.read(); // Actively read data once
await transfers data to the cloud (latest data.temperature); // transfers to the cloud
    
, 60 * 1000); // Transfer data once a minute
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Scene Expansion: Change the temperature to heart rate and you can do health monitoring; change it to light intensity and you can automatically adjust the screen brightness – only you can’t imagine, but you can’t do it without the system’s ability!



Chapter 4: The guide to avoid pits: “Unfacing Rules” for Calling System Capabilities

  1. Permission number one:
    Call sensors, network and other capabilities, declare permissions in config.json first, otherwise you will be “rejected” by the system~ 
   
     "reqPermissions": [
       
         "name": "ohos.permission.GET_SENSOR_DATA"
       ,
       
         "name": "ohos.permission.INTERNET"
       
     ]
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  1. Async processing:
    Most system capability calls are asynchronous. Remember to use async/await or .then() to not let the code “stuck” ~
  2. Resource Recycling:
    Open file streams and subscribed sensors, remember to close them after using them!Otherwise, the memory will be like a “leaked bucket”, and the more you use it, the less you use it~



Last chat

System capability calling is like learning to drive: at first I feel complicated (remember various APIs), but after being proficient, you can “storm all the way” ~ Next time I will tell you how to use device management capabilities to “application performance optimization”, and by the way, “how to make the APP as lightweight and power-saving as a cat”, remember to follow!😉

(Please indicate the source and original author Xiao L when reprinting. Violators… Let your code report permission errors every day! Haha~)



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