MMKV is an efficient, small, easy-to-use mobile key-value storage framework used in the WeChat application. It's now available on HarmonyOS NEXT.

MMKV for HarmonyOS NEXT

Features

• Efficient. MMKV uses mmap to keep memory synced with file, and protobuf to encode/decode values, making the most of native platform to achieve best performance.

  • Multi-Process concurrency: MMKV supports concurrent read-read and read-write access between processes.

• Easy-to-use. You can use MMKV as you go. All changes are saved immediately, no sync, no flush calls needed.

• Small.

  • A handful of files: MMKV contains process locks, encode/decode helpers and mmap logics and nothing more. It's really tidy.
  • About 600K in binary size: MMKV adds about 600K per architecture on App size, and much less when zipped (HAR/HAP).

Getting Started

Prerequisites

• Apps using MMKV can target: HarmonyOS Next (Canary 2) or later.
• ARM64 & x86_64 architecture.
• DevEco Studio NEXT Developer Beta1 (5.0.3.100) or later.

Installation via OHPM:

This is the fastest and recommended way to add MMKV to your project.

ohpm install @tencent/mmkv

Or, you can add it to your project manually.

• Add the following lines to oh-package.json5 on your app module.

  "dependencies": {
      "@tencent/mmkv": "1.3.5",
  }

• Then run

  ohpm install

For additional installation methods, checkout the wiki.

Setup

You can use MMKV as you go. All changes are saved immediately, no sync, no apply calls needed.
Setup MMKV on App startup, say your EntryAbility.onCreate() function, add these lines:

import { MMKV } from '@tencent/mmkv';

export default class EntryAbility extends UIAbility {
  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    let appCtx = this.context.getApplicationContext();
    let mmkvRootDir = MMKV.initialize(appCtx);
    console.info('mmkv rootDir: ', mmkvRootDir);
    ……
  }

CRUD Operations

• MMKV has a global instance, that can be used directly:

  import { MMKV } from '@tencent/mmkv';
      
  let mmkv = MMKV.defaultMMKV();
  mmkv.encodeBool('bool', true);
  console.info('bool = ', mmkv.decodeBool('bool'));
  
  mmkv.encodeInt32('int32', Math.pow(2, 31) - 1);
  console.info('max int32 = ', mmkv.decodeInt32('int32'));
  
  mmkv.encodeInt64('int', BigInt(2**63) - BigInt(1));
  console.info('max int64 = ', mmkv.decodeInt64('int'));
  
  let str: string = 'Hello OpenHarmony from MMKV';
  mmkv.encodeString('string', str);
  console.info('string = ', mmkv.decodeString('string'));
  
  let arrayBuffer: ArrayBuffer = StringToArrayBuffer('Hello OpenHarmony from MMKV with bytes');
  mmkv.encodeBytes('bytes', arrayBuffer);
  let bytes = mmkv.decodeBytes('bytes');
  console.info('bytes = ', ArrayBufferToString(bytes));

  As you can see, MMKV is quite easy to use.

• Deleting & Querying:

  mmkv.removeValue('bool');
  console.info('contains "bool"', mmkv.containsKey('bool'));
  
  mmkv.removeValues(['int32', 'int']);
  console.info('all keys: ', mmkv.allKeys().join());

• If different modules/logic need isolated storage, you can also create your own MMKV instance separately:

  var mmkv = MMKV.mmkvWithID('test');
  mmkv.encodeBool('bool', true);
  console.info('bool = ', mmkv.decodeBool('bool'));

• If multi-process accessing is needed，you can set MMKV.MULTI_PROCESS_MODE on MMKV initialization:

  var mmkv = MMKV.mmkvWithID('test-multi-process', MMKV.MULTI_PROCESS_MODE);
  mmkv.encodeBool('bool', true);
  console.info('bool = ', mmkv.decodeBool('bool'));

Supported Types

• Primitive Types:

  • boolean, number, bigint, string

• Classes & Collections:

  • boolean[], number[], string[], ArrayBuffer

Log

• By default, MMKV prints log to hilog, which is not convenient for diagnosing online issues. You can setup MMKV log redirecting on App startup on the native interface of MMKV. Checkout how to do it on C++. Due to the current limitation of NAPI runtime, we can't efficiently redirect log to the JavaScript side.

• You can turn off MMKV's logging once and for all on initialization (which we strongly disrecommend).

  import { MMKV, MMKVLogLevel } from '@tencent/mmkv';
  
  MMKV.initialize(appCtx, MMKVLogLevel.None);

Encryption

• By default MMKV stores all key-values in plain text on file, relying on Android's/iOS's sandbox to make sure the file is encrypted. Should you worry about information leaking, you can choose to encrypt MMKV.

  let encryptKey = 'MyEncryptKey';
  let mmkv = MMKV.mmkvWithID('test-encryption', MMKV.SINGLE_PROCESS_MODE, encryptKey);

• You can change the encryption key later as you like. You can also change an existing MMKV instance from encrypted to unencrypted, or vice versa.

  // an unencrypted MMKV instance
  let mmkv = MMKV.mmkvWithID('test-encryption');
  
  // change from unencrypted to encrypted
  mmkv.reKey('Key_seq_1');
  
  // change encryption key
  mmkv.reKey('Key_seq_2');
  
  // change from encrypted to unencrypted
  kmmkv.reKey();

Customize location

• By default, MMKV stores file inside $(FilesDir)/mmkv/. You can customize MMKV's root directory on App startup:

  let appCtx = this.context.getApplicationContext();
  let rootDir = appCtx.filesDir + '/mmkv_2';
  let cacheDir = appCtx.cacheDir;
  MMKV.initialize(rootDir, cacheDir);

• You can even customize any MMKV instance's location:

  let appCtx = this.context.getApplicationContext();
  let rootDir = appCtx.filesDir + '/mmkv_3';
  var mmkv = MMKV.mmkvWithID('testCustomDir', MMKV.SINGLE_PROCESS_MODE, null, rootDir);

  Note: It's recommended to store MMKV files inside your App's sandbox path. DO NOT store them on external storage(aka SD card).

Additional docs

For additional documents, checkout the wiki.

License

MMKV is published under the BSD 3-Clause license. For details check out the LICENSE.TXT.

Change Log

Check out the CHANGELOG.md for details of change history.

Contributing

If you are interested in contributing, check out the CONTRIBUTING.md, also join our Tencent OpenSource Plan.

To give clarity of what is expected of our members, MMKV has adopted the code of conduct defined by the Contributor Covenant, which is widely used. And we think it articulates our values well. For more, check out the Code of Conduct.

FAQ & Feedback

Check out the FAQ first. Should there be any questions, don't hesitate to create issues.