Kotlin shared preferences

Question

So I've written a class for storing user/device specific settings, but I've written the Kotlin pretty much like I would in Java:

import android.content.Context
import android.content.SharedPreferences
import java.util.*
class UserSettings {
 private lateinit var _prefs :SharedPreferences
 fun UserSettings(ctx : Context) {
 _prefs = ctx.getSharedPreferences("UserSettings", Context.MODE_PRIVATE)
 }
 private val KEY_DEVICEID = "deviceId"
 var deviceId :String
 get() {
 var value = _prefs.getString(KEY_DEVICEID, null)
 if (null == value) {
 value = UUID.randomUUID().toString()
 this.deviceId = value
 }
 return value
 }
 set(it) {
 _prefs.edit()
 .putString(KEY_DEVICEID, it)
 .apply()
 }
}

This feels really verbose. I've considered writing a helper library to simply store all values from a class in SharedPreferences via reflection, but I'm not sure if that's overkill. The above code obviously only has one value at the moment, but I'll be adding a couple more that will look very similar to the above.

Answer 1

Welcome to Kotlin! Consider this.

// Define constructor this way
class UserSettings(context: Context) {
 // Prefixes for fields are rather uncommon in the Kotlin world.
 // You could remove the type declaration here - Kotlin will infer it for you
 private val prefs: SharedPreferences = context
 .getSharedPreferences("UserSettings", Context.MODE_PRIVATE)
 var deviceId: String
 get() = prefs.getString(KEY_DEVICE_ID, null) ?: UUID.randomUUID().toString().also {
 // `also` block will execute only in case we return a new UUID.
 deviceId = it
 }
 set(it) {
 prefs
 .edit()
 .putString(KEY_DEVICE_ID, it)
 .apply()
 }
 companion object {
 // Depends on a taste / convention your team uses.
 // I like keeping my key constants within the companion object.
 private const val KEY_DEVICE_ID = "deviceId"
 }
}

For simplifying it even more, consider using Android KTX - it has some handy SharedPreferences extensions, described here: https://developer.android.com/kotlin/ktx