Singleton Shared Preference

gistfile1.txt

object AppPreferences {
    private const val NAME = "SpinKotlin"
    private const val MODE = Context.MODE_PRIVATE
    private lateinit var preferences: SharedPreferences
    // list of app specific preferences
    private val IS_FIRST_RUN_PREF = Pair("is_first_run", false)
    
    fun init(context: Context) {
        preferences = context.getSharedPreferences(NAME, MODE)
    }
    
    /**
     * SharedPreferences extension function, so we won't need to call edit() and apply()
     * ourselves on every SharedPreferences operation.
     */
    private inline fun SharedPreferences.edit(operation: (SharedPreferences.Editor) -> Unit) {
        val editor = edit()
        operation(editor)
        editor.apply()
    }
    
    var firstRun: Boolean
        // custom getter to get a preference of a desired type, with a predefined default value
        get() = preferences.getBoolean(IS_FIRST_RUN_PREF.first, IS_FIRST_RUN_PREF.second)
        // custom setter to save a preference back to preferences file
        set(value) = preferences.edit {
            it.putBoolean(IS_FIRST_RUN_PREF.first, value)
        }
}

gistfile2.txt

class SpInKotlinApp : Application() {
    override fun onCreate() {
        super.onCreate()
        AppPreferences.init(this)
    }
}

gistfile3.txt

class MainActivity : AppCompatActivity() {
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        
        if (!AppPreferences.firstRun) {
            AppPreferences.firstRun = true
            Log.d("SpinKotlin", "The value of our pref is: ${AppPreferences.firstRun}")
        }
    }
}