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