Shared Preferences as Property Delegates (from the Kotlin for Android Developers book)

Preference.kt

package com.talkingkotlin.util

import android.annotation.SuppressLint
import android.content.Context
import android.content.SharedPreferences
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

/**
 * Shared Preferences as Property Delegates (from the Kotlin for Android Developers book)
 * @author Alexander Gherschon
 */

class Preference<T>(
        private val context: Context,
        private val name: String,
        private val default: T): ReadWriteProperty<Any?, T> {

    private val prefs: SharedPreferences by lazy {
        context.getSharedPreferences("default", Context.MODE_PRIVATE)
    }

    override fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return findPreference(name, default)
    }

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        putPreference(name, value)
    }

    private fun <T> findPreference(name: String, default: T): T = with(prefs) {
        val res: Any = when (default) {
            is Long -> getLong(name, default)
            is String -> getString(name, default)
            is Int -> getInt(name, default)
            is Boolean -> getBoolean(name, default)
            is Float -> getFloat(name, default)
            else -> throw IllegalArgumentException("This type cannot be saved into Preferences")
        }
        @Suppress("UNCHECKED_CAST")
        res as T
    }

    @SuppressLint("CommitPrefEdits")
    private fun <T> putPreference(name: String, value: T) = with(prefs.edit()) {
        when (value) {
            is Long -> putLong(name, value)
            is String -> putString(name, value)
            is Int -> putInt(name, value)
            is Boolean -> putBoolean(name, value)
            is Float -> putFloat(name, value)
            else -> throw IllegalArgumentException("This type cannot be saved into Preferences")
        }.apply()
    }
}

FYI, this will crash if you try to set to null, or if you set null as your default value

how to put a value in preferences using this implementation??

How to save value in preference when try to do it is not working.

I have solved my problem fallowing [https://trivedihardik.wordpress.com/2017/08/01/kotlin-sharedpreferences-using-delegated-property/](Shared Preference with Delegate)
In this blog it is clearly explained.