MMKV-KTX

MMKV-KTX is an extension of MMKV designed to offer a seamless key-value storage solution for Kotlin, integrating tightly with the language's syntax and features.

Features

• Kotlin-Friendly: Designed specifically for Kotlin, offering idiomatic syntax and integration.
• Class Mapping: Automatically maps Kotlin data classes to key-value storage for easy use.
• Type Safety: Supports custom type converters to securely store a wide range of data types.
• Compile-Time Processing: Employs Kotlin Symbol Processing (KSP) for compile-time code generation, ensuring type safety and reducing runtime overhead.

Table of Contents

• Features
• Getting Started
  • Apply KSP Plugin
  • Configure KSP Argument
  • Import Dependencies
• Basic Usage
  • Initialization
  • Declaring Data and Converters
  • Reading and Writing Preferences
  • Reactive Support (Kotlin Flow)
• Advanced
  • Integrated with ViewModel and Hilt
  • Integrated with Jetpack Compose
• Contributing

Getting Started

Apply KSP Plugin

MMKV-KTX relies on compile-time code generation, so please make sure that KSP is enabled in your module's build.gradle.kts:

plugins {
  id("com.google.devtools.ksp") version "<ksp_version>" // Replace it with your desired version
}

Important

Select a KSP version compatible with your Kotlin version.

Configure KSP Argument

Specify the package name for the generated code in your build.gradle.kts:

ksp.arg("mmkv.ktx.packageName", "<your_package>") // Replace it with your desired package, e.g. 'com.meowool.myapp.codegen'

Import Dependencies

Depending on your project setup, follow the appropriate steps to include MMKV-KTX in your project.

without Version Catalog

build.gradle.kts

dependencies {
  val mmkvKtxVersion = "0.1.4"
  implementation("com.meowool:mmkv:$mmkvKtxVersion")
  ksp("com.meowool:mmkv-compiler:$mmkvKtxVersion")
}

using Version Catalog

libs.versions.toml

[versions]
mmkv-ktx = "0.1.4"

[librarys]
mmkv-ktx = { module = "com.meowool:mmkv", version.ref = "mmkv-ktx" }
mmkv-ktx-compiler = { module = "com.meowool:mmkv-compiler", version.ref = "mmkv-ktx" }

build.gradle.kts

dependencies {
  implementation(mmkv.ktx)
  ksp(mmkv.ktx.compiler)
}

MMKV-KTX is published on Maven Central, so if you haven't defined the repository yet, please do it:

repositories {
  mavenCentral()
}

Basic Usage

MMKV-KTX greatly simplifies the usage of key-value storage in Kotlin. As a result, you can almost immediately understand how to use it just by looking at the following example.

Initialization

Before starting, please make sure you have initialized the MMKV instance. If not, initialize it anywhere that can access the Context, such as in the Application:

class YourApplication : Application() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    MMKV.initialize(this)
  }
}

Declaring Data and Converters

Use annotations to define your preferences:

import java.util.UUID
import com.meowool.mmkv.ktx.Preferences
import com.meowool.mmkv.ktx.PersistDefaultValue

// @androidx.compose.runtime.Immutable (If you use Jetpack Compose, you can mark it as immutable)
@Preferences
data class UserSettings(
  val themeAppearance: ThemeAppearance = ThemeAppearance.Auto,
  val customToken: String? = null,
  val notificationsEnabled: Boolean = true,
)

// @androidx.compose.runtime.Immutable
@Preferences
data class GlobalData(
  @PersistDefaultValue // If needed
  val id: UUID = UUID.randomUUID(),
  val isLoggedIn: Boolean = true,
)

enum class ThemeAppearance { Light, Dark, Auto }

In this example, we have data of primitive types, enum types, and UUID. While the MMKV-KTX compiler supports most types by default, allowing for an out-of-the-box experience, using unsupported types (like UUID in our example) requires custom converters.

For more information on supported types, please refer to Annotation Document

Define your type converters:

import com.meowool.mmkv.ktx.TypeConverters

@TypeConverters
class Converters {
  fun UUID.toBytes(): ByteArray = ByteBuffer.allocate(16).apply {
    putLong(mostSignificantBits)
    putLong(leastSignificantBits)
  }.array()
  
  fun ByteArray.toUUID(): UUID = with(ByteBuffer.wrap(this)) {
    UUID(long, long)
  }
}

This setup allows you to freely convert custom types, ensuring that the MMKV-KTX compiler can handle a wide range of data types without built-in support.

Reading and Writing Preferences

All preference instances are encapsulated within the PreferencesFactory object, making it the central point for operations. In the example provided above, we can access the PreferencesFactory.userSettings and PreferencesFactory.globalData properties by instantiating a PreferencesFactory object.

// Declare top-level static instance or inject a singleton with the DI pattern (e.g. Hilt)
val preferences: PreferencesFactory = PreferencesFactory()

fun anywhere() {
  println(preferences.globalData.get().id)
  println(preferences.userSettings.get().notificationsEnabled)
}

The userSettings and globalData properties are automatically named based on the names of the preference data classes. You can also customize their names using @Preferences(name = "customPropertyName").

Updating preferences is equally straightforward:

fun resetUserSettings() = preferences.userSettings.update {
  it.themeAppearance = ThemeAppearance.Auto
  it.customToken = null
  it.notificationsEnabled = true
}

Reactive Support (Kotlin Flow)

Sometimes you may also want to be able to get the latest value in real time. MMKV-KTX provides kotlinx.flow conversion to make things incredibly easy.

To instantly react whenever the data changes, you can use the asStateFlow function to convert preferences into a hot flow (StateFlow) that you are familiar with (assuming you often use Kotlin Flow).

val userSettings: StateFlow<UserSettings> = preferences.userSettings.asStateFlow()

suspend fun log() = userSettings.collect {
  println("UserSettings updated: $it")
}

Additionally, you can use mapStateFlow to map changes to another value whenever data changes occur:

val notifications: StateFlow<NotificationsController?> = preferences.userSettings.mapStateFlow {
  if (it.notificationsEnabled) Factory.notificationsController else null
}

For more detailed usage instructions and examples, please refer to the documentation for each annotation/function.

Advanced

In case you are interested in other usage methods, here are some common uses listed here.

Integrated with ViewModel and Hilt

import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.components.SingletonComponent
import javax.inject.Singleton
import <your_package>.PreferencesFactory
import <your_package>.GlobalDataPreferences
import <your_package>.UserSettingsPreferences

@Module
@InstallIn(SingletonComponent::class)
class PreferencesModule {
  @Provides
  @Singleton
  fun providesPreferencesFactory(): PreferencesFactory = PreferencesFactory()

  @Provides
  fun providesGlobalDataPreferences(preferences: PreferencesFactory): GlobalDataPreferences = preferences.globalData

  @Provides
  fun providesUserSettingsPreferences(preferences: PreferencesFactory): UserSettingsPreferences = preferences.userSettings
}

class SettingsViewModel(
  private val globalData: GlobalDataPreferences,
  private val userSettings: UserSettingsPreferences,
) : ViewModel() {
  val followingSystemTheme = userSettings.mapStateFlow {
    it.themeAppearance == ThemeAppearance.Auto
  }
  
  fun saveToken(value: String) {
    checkToken(value) { ... }
    userSettings.update {
      it.customToken = TokenFactory.newTokenString(
        appId = globalData.get().id,
        token = value,
      )
    }
  }
}

Integrated with Jetpack Compose

In the world of Jetpack Compose, there's nothing particularly special about using it, just for your reference:

@Composable
fun AppTheme(content: @Composable () -> Unit) {
  val systemInDark = isSystemInDarkTheme()
  val preferences: PreferencesFactory = remember { PreferencesFactory() }
  val usingDarkTheme by preferences.userSettings.mapStateFlow { setting ->
    when (setting.themeAppearance) {
      ThemeAppearance.Light -> false
      ThemeAppearance.Dark -> true
      ThemeAppearance.Auto -> systemInDark
    }
  }.collectAsStateWithLifecycle(initialValue = systemInDark)

  MaterialTheme(
    colors = if (usingDarkTheme) DarkColorPalette else LightColorPalette,
    content = content,
  )
}

Contributing

Contributions to MMKV-KTX are welcome! Please feel free to submit pull requests or open issues to improve the library or documentation.

License

MMKV-KTX is released under the Apache License 2.0. See the LICENSE file for more details.