Flow Preferences

This is the Kotlin Flow version of rx-preferences. It follows pretty much the same API and should feel familiar to anyone with experience there. But instead of RxJava, we have Coroutines -- mainly Flows.

Download

repositories {
  mavenCentral()
}

dependencies {
  implementation 'com.fredporciuncula:flow-preferences:1.9.1'
}

How it looks like

Start with the regular SharedPreferences:

val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context)

Create an instance of FlowSharedPreferences from that:

val flowSharedPreferences = FlowSharedPreferences(sharedPreferences)

Get a preference:

val myPref = flowSharedPreferences.getInt("key", defaultValue = 10)

Go with the Flow:

myPref.asFlow().onEach { print(it) }.launchIn(scope)

Extras

Set and commit support

Preferences expose the regular get() and put() (named as set()) functions from SharedPreferences. But in addition to that, they also expose the suspend setAndCommit() function that puts the value and performs a commit in case you must ensure the preference is persisted right away. There's also a deleteAndCommit().

Collector support

You can call asCollector() to ask a FlowCollector from a preference. You can then persist values from a Flow directly to the preference:

val flow = flow { emit(1) }

scope.launch {
  myPref.asCollector().emitAll(flow)
}

You can use asSyncCollector() if you want to put and commit the value (like setAndCommit()) on each emission.

Enum support

Enum classes work out of the box and are persisted as strings based on their name value (so make sure you @Keep them if you're using R8):

enum class MyEnum { A, B, C }

val myPref = flowSharedPreferences.getEnum("key", defaultValue = MyEnum.A)

Object support

Arbitrary objects are also supported as long as an instance of ObjectPreference.Serializer is provided:

class TestObject(val id: Int)

val serializer =
  object : ObjectPreference.Serializer<TestObject> {
    override fun deserialize(serialized: String) = TestObject(serialized.toInt())
    override fun serialize(value: TestObject) = value.id.toString()
  }

val myPref = flowSharedPreferences.getObject("key", serializer, defaultValue = TestObject(0))

Explicit nullability support

By default, strings, objects, enums and sets can never be null, so consumers don't ever have to worry about null checks. If you want to support nullable values, you can explicitly opt in by asking for the nullable-friendly preference types:

val nullableStringPreference = flowSharedPreferences.getNullableString("key", defaultValue = null)

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