Introduction: A Kotlin Multiplatform library for mobile apps to save settings as key-value pairs
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This is a Kotlin library for Multiplatform mobile apps, so that common code can persist key-value data. It stores things using SharedPreferences on Android and NSUserDefaults on iOS.

Adding to your project

First, add the multiplatform-settings bintray url to the repositories block of any module using it.

repositories {
    maven { url = '' }

Then, simply add the dependency to your common source-set dependencies

implementation "com.russhwolf:multiplatform-settings:0.2"

See also the sample project, which uses this structure.


The Settings interface is implemented by the PlatformSettings class, which has separate implementations for Android and iOS. A PlatformSettings instance can be created using a platform-specific factory. On Android, this factory needs a Context parameter

val context: Context = ...
val factory: Settings.Factory = PlatformSettings.Factory(context)

On iOS, the factory can be instantiated without passing any parameter

val factory: Settings.Factory = PlatformSettings.Factory()

Using a factory allows for creating a Settings instance using the same name parameter on both platforms. This parameter is optional and a platform-specific default will be used if it is absent.

val settings: Settings = factory.create("my_settings_name")

Alternatively, you can create a PlatformSettings instance by passing the platform-specific delegate class that PlatformSettings wraps around. On Android,

val delegate: SharedPreferences = ...
val settings: Settings = PlatformSettings(delegate)

And on iOS,

val delegate: NSUserDefaults = ...
val settings: Settings = PlatformSettings(delegate)    

Once the Settings instance is created, you can store values by calling the various putXXX() methods, or their operator shortcuts

settings.putInt("key", 3)
settings["key"] = 3

You can retrieve stored values via the getXXX() methods or their operator shortcuts. If a key is not present, then the supplied default will be returned instead.

val a: Int = settings.getInt("key")
val b: Int = settings.getInt("key", defaultValue = -1) 
val c: Int = settings["key", -1]

The getXXX() and putXXX() operation for a given key can be wrapped using a property delegate. This has the advantage of ensuring that the key is always accessed with a consistent type.

val a: Int by"key")
val b: Int by"key", defaultValue = -1)

val c: Int? by settings.nullableInt("another_key")

Existence of a key can be queried

val a: Boolean = settings.hasKey("key")
val b: Boolean = "key" in settings

Values can also be removed by key

settings -= "key"  

Finally, all values in a Settings instance can be removed


Experimental API


Update listeners are available using an experimental API.

val settingsListener: SettingsListener = settings.addListener(key) { ... }

The SettingsListener returned from the call should be used to signal when you're done listening:


This initial listener implementation is not designed with any sort of thread-safety so it's recommended to only interact with these APIs from the main thread of your application.

The listener APIs make use of the Kotlin @Experimental annotation. All usages must be marked with @ExperimentalListener or @UseExperimental(ExperimentalListener::class).

Project Structure

The library logic lives in the commonMain, androidMain, and iosMain sources. The common source holds the Settings interface and an expect implementation called PlatformSettings. These expose apis for persisting values of the Int, Long, String, Float, Double, and Boolean types. The common source also holds property delegate wrappers and other operator functions for cleaner syntax and usage. The android and ios modules then hold actual declarations, delegating to SharedPreferences or NSUserDefaults.

Some simple unit tests are defined which can be run via ./gradlew test. These use Robolectric on Android to mock out the android-specific behavior, and use the ios simulator to run the native tests.

There is also a sample project to demonstrate usage, which is configured as a separate IDEA/gradle project in the sample directory. It includes a shared module with common and platform sources, to demo a shared logic layer consuming the library. The app-android module consumes shared and provides an Android UI. The app-ios directory holds an Xcode project which builds an iOS app in the usual way, consuming a framework produced by shared.

The shared module includes some simple unit tests in common code to demonstrate a way to mock out the Settings interface when testing code that interacts with it.


Copyright 2018 Russell Wolf

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
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