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

[Lomanu4]

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);
}
}

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 | fs.OpenMode.WRITE);
// Create an output stream and prepare to "start a pen"
const output stream = await fs.createOutputStream(file);
// Writing data is like writing words on a notebook
const content = new TextEncoder().encode('This is Xiao L's code notes~');
await output stream.write(content);
console.log('Written successfully, the file now has words!');
// Close the notebook (close the stream)
await output stream.close();
await fs.close(file);
} catch (error) {
console.error('Failed to write file:' + error.message);
}
}

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"~');
}
}
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: '

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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
}
}
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

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"
}
]
}

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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