preferences

KTX: preference utilities

Utilities and extension function for LibGDX preferences.

Why?

LibGDX Preferences do not provide a consistent API for setting and getting values, and they do not support Kotlin operators either. Since in principle Preferences work very similarly to a Map, ideally they should support a similar syntax - especially since in Kotlin you can take advantage of the square bracket operators.

Guide

• Values can be set and read via the new set and get operators using the square bracket ([]) syntax. It is no longer necessary to call type specific methods like putString or getBoolean for each type separately. set and get support objects of any type. If the type is not of String, Boolean, Int, Float, Double or Long type, the value is stored and retrieved using JSON serialization.
  • Note that Double type is not supported by LibGDX Preferences and converted to Float instead. Use explicit casts (toFloat()) or wrap the value with a JSON-serializable object when storing numbers that do not fit in a Float.
• Preferences can now be set with a Pair<String, Any> parameter. Keys and values can be paired using the standard library to infix function.
• New flush extension supports a lambda parameter to easily update the Preferences before flushing.

Usage examples

Reading basic application preferences:

import com.badlogic.gdx.Gdx
import ktx.preferences.*

fun readValuesFromPreferences() {
  val preferences = Gdx.app.getPreferences("myPreferences")
  // Accessing preferences by keys passed as parameters:
  val string: String? = preferences["SomeString"]
  val float: Float? = preferences["SomeFloat"]
  val boolean: Boolean? = preferences["SomeBoolean"]
  val integer: Int? = preferences["SomeInt"]
  val long: Long? = preferences["SomeLong"]
  // Do something with preferences here.
}

Reading basic preferences with custom default values in case they are missing:

import com.badlogic.gdx.Preferences
import ktx.preferences.*

fun readValuesWithDefaultsFromPreferences(preferences: Preferences) {
  // If the key (given as the first parameter) is absent in the preferences,
  // the default value (passed as the second parameter) will be returned:
  val string: String = preferences["SomeString", "default value"]
  val float: Float = preferences["SomeFloat", 2.0f]
  val boolean: Boolean = preferences["SomeBoolean", true]
  val integer: Int = preferences["SomeInt", 42]
  val long: Long = preferences["SomeLong", 3L]
  // Alternative syntax without the [] operator:
  val preference = preferences.get<Int>("Key", defaultValue = 42)
  // Do something with preferences here.
}

Loading objects serialized as JSON from preferences:

import com.badlogic.gdx.Preferences
import ktx.preferences.*

/**
 * This class will be serialized.
 * 
 * Remember to add default values for each variable,
 * so the class remains JSON-serializable!
 */
data class Player(val name: String = "Player", val life: Int = 100)

fun readObjectFromPreferences(preferences: Preferences): Player? {
  // Will automatically deserialize the object from JSON:
  return preferences["Player"]
}

Saving preferences:

import com.badlogic.gdx.Preferences
import ktx.preferences.*

fun saveInPreferences(
    preferences: Preferences,
    string: String, float: Float, bool: Boolean, int: Int, long: Long) {
  // The values will be stored in preferences under the given keys:
  preferences["SomeString"] = string
  preferences["SomeFloat"] = float
  preferences["SomeBoolean"] = bool
  preferences["SomeInt"] = int
  preferences["SomeLong"] = long
  // Remember to call flush in order to save the preferences:
  preferences.flush()
}

Saving preferences with automatic flushing using flush extension method:

import com.badlogic.gdx.Preferences
import ktx.preferences.*

fun saveInPreferencesWithFlush(
    preferences: Preferences,
    string: String, float: Float, bool: Boolean, int: Int, long: Long) {
  preferences.flush {
    // This extension method changes `this` to preferences within the scope:
    this["SomeString"] = string
    this["SomeFloat"] = float
    this["SomeBoolean"] = bool
    this["SomeInt"] = int
    this["SomeLong"] = long 
    // preferences.flush() will be called automatically after this block.
  }
}

Saving objects as JSON in preferences:

import com.badlogic.gdx.Preferences
import ktx.preferences.*

data class Player(val name: String = "Player", val life: Int = 100)

fun saveObjectInPreferences(preferences: Preferences, player: Player) {
  preferences.flush {
    // Will automatically serialize the object to JSON:
    this["Player"] = player
  }
}

Setting preferences using Kotlin pairs and to infix function:

import com.badlogic.gdx.Preferences
import ktx.preferences.*

data class Player(val name: String = "Player", val life: Int = 100)

fun addPreferencesUsingKotlinPairs(preferences: Preferences) {
  preferences.set("SomeInt" to 1)
  preferences.set("SomeFloat" to 1.0f)
  preferences.set("SomeLong" to 1L)
  preferences.set("SomeBoolean" to true)
  preferences.set("SomeString" to "value")
  preferences.set("Player" to Player(name = "Example", life = 75))
}

Additional documentation

• Official LibGDX Preferences article.
• Official LibGDX Json article.