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MMKV is an efficient, small, easy-to-use mobile key-value storage framework used in the WeChat application. It's currently available on Android and iOS.

MMKV for Flutter

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 apply 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 100K in binary size: MMKV adds about 100K per architecture on App size, and much less when zipped (apk/ipa).

Getting Started

Installation

Add the following lines to pubspec.yaml on your app module. Then run flutter pub get.

dependencies:
  mmkv: ">=1.2.10"
  ...

If you already include MMKV native lib in your App, you need to upgrade to version newer than v1.2.9.

iOS

To avoid conflict of the native lib name 'libMMKV.so' on iOS, we need to change the plugin name 'mmkv' to 'mmkvflutter'.

For a purely flutter App:
  • Add this function fix_mmkv_plugin_name() to ios/Podfile, invoke it before calling any flutter_xxx() functions. Run pod install and we are all set.
  • Note: you need to run pod install each time you have called flutter pub get, or has just returned to Xcode from Android Studio.
  • We recommend using Xcode to debug iOS App.
def fix_mmkv_plugin_name(flutter_application_path)
  is_module = false
  plugin_deps_file = File.expand_path(File.join(flutter_application_path, '..', '.flutter-plugins-dependencies'))
  if not File.exists?(plugin_deps_file)
    is_module = true;
    plugin_deps_file = File.expand_path(File.join(flutter_application_path, '.flutter-plugins-dependencies'))
  end

  plugin_deps = JSON.parse(File.read(plugin_deps_file)).dig('plugins', 'ios') || []
  plugin_deps.each do |plugin|
    if plugin['name'] == 'mmkv' || plugin['name'] == 'mmkvflutter'
      require File.expand_path(File.join(plugin['path'], 'tool', 'mmkvpodhelper.rb'))
      mmkv_fix_plugin_name(flutter_application_path, is_module)
      return
    end
  end
  raise "Fail to find any mmkv plugin dependencies. If you're running pod install manually, make sure flutter pub get is executed first"
end

fix_mmkv_plugin_name(File.dirname(File.realpath(__FILE__)))
For using flutter as a module:
  • For embding flutter to your existing iOS App, add the function fix_mmkv_plugin_name() above to your iOS App's Podfile, invoke it before calling any flutter_xxx() functions. Run pod install and we are all set.
  • Note: you need to run pod install each time you have called flutter pub get, or has just returned to Xcode from Android Studio.
  • We recommend using Xcode to debug iOS App.
def fix_mmkv_plugin_name(flutter_application_path)
  .....
end

flutter_application_path = 'path/to/your/flutter_module'

fix_mmkv_plugin_name(flutter_application_path)

Note: You can find the script inside mmkv plugin under path tool/fix_mmkv_plugin_name.rb.

Android

If you previously use com.tencent.mmkv in your Android App, you should move to com.tencent.mmkv-static. And if your App depends on any 3rd SDK that embeds com.tencent.mmkv, you can add this lines to your build.gradle to avoid conflict:

    dependencies {
        ...

        modules {
            module("com.tencent:mmkv") {
                replacedBy("com.tencent:mmkv-static", "Using mmkv-static for flutter")
            }
        }
    }

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 main() function, add these lines:

import 'package:mmkv/mmkv.dart';

void main() async {

  // must wait for MMKV to finish initialization
  final rootDir = await MMKV.initialize();
  print('MMKV for flutter with rootDir = $rootDir');

  runApp(MyApp());
}

Note that you have to wait for MMKV to finish initialization before accessing any MMKV instance.

CRUD Operations

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

      import 'package:mmkv/mmkv.dart';
    
      var mmkv = MMKV.defaultMMKV();
      mmkv.encodeBool('bool', true);
      print('bool = ${mmkv.decodeBool('bool')}');
    
      mmkv.encodeInt32('int32', (1<<31) - 1);
      print('max int32 = ${mmkv.decodeInt32('int32')}');
    
      mmkv.encodeInt('int', (1<<63) - 1);
      print('max int = ${mmkv.decodeInt('int')}');
    
      String str = 'Hello Flutter from MMKV';
      mmkv.encodeString('string', str);
      print('string = ${mmkv.decodeString('string')}');
    
      str = 'Hello Flutter from MMKV with bytes';
      var bytes = MMBuffer.fromList(Utf8Encoder().convert(str))!;
      mmkv.encodeBytes('bytes', bytes);
      bytes.destroy();
    
      bytes = mmkv.decodeBytes('bytes')!;
      print('bytes = ${Utf8Decoder().convert(bytes.asList()!)}');
      bytes.destroy();
    

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

    Note: If you come across to failing to load defaultMMKV() on Android after upgrading Flutter from 1.20+ to 2.0+, you can try passing this encryption key '\u{2}U' instead.

     var mmkv = MMKV.defaultMMKV(cryptKey: '\u{2}U');
    
  • Deleting & Querying:

      var mmkv = MMKV.defaultMMKV();
    
      mmkv.removeValue('bool');
      print('contains "bool": ${mmkv.containsKey('bool')}');
    
      mmkv.removeValues(['int32', 'int']);
      print('all keys: ${mmkv.allKeys}');
    
  • If different modules/logic need isolated storage, you can also create your own MMKV instance separately:

      var mmkv = MMKV("test");
      mmkv.encodeBool('bool', true);
      print('bool = ${mmkv.decodeBool('bool')}');
    
  • If multi-process accessing is needed´╝îyou can set MMKV.MULTI_PROCESS_MODE on MMKV initialization:

      var mmkv = MMKV("test-multi-process", mode: MMKVMode.MULTI_PROCESS_MODE);
      mmkv.encodeBool('bool', true);
      print('bool = ${mmkv.decodeBool('bool')}');
    

Supported Types

  • Primitive Types:

    • bool, int, double
  • Classes & Collections:

    • String, List<int>, MMBuffer

Log

  • By default, MMKV prints log to logcat/console, 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 Android / iOS. Due to the current limitation of Flutter runtime, we can't redirect log on the Flutter side.

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

      final rootDir = await MMKV.initialize(logLevel: 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.

      final encryptKey = 'MyEncryptKey';
      var mmkv = MMKV("test-encryption", cryptKey: 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
      var mmkv = MMKV("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(null);
    

Customize location

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

      final dir = await getApplicationSupportDirectory();
      final rootDir = await MMKV.initialize(dir, rootDir: dir.path + '/mmkv_2');
      print('MMKV for flutter with rootDir = $rootDir');
    
  • You can even customize any MMKV instance's location:

      final dir = await getApplicationSupportDirectory();
      var mmkv = MMKV('testCustomDir', rootDir: dir.path + '/mmkv_3');
    

    Note: It's recommended to store MMKV files inside your App's sandbox path. DO NOT store them on external storage(aka SD card). If you have to do it, you should follow Android's scoped storage enforcement.

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.

Libraries

mmkv