SharedPreferences under Delegated properties - PreferencesDelegate getValue().

PreferencesDelegate.kt

open class PreferencesDelegate<T>(private val key: String) {
    private var variable: Any? = null
    private var initialized = false

    /**
     * Return desired value by a given key. Performing operation on synchronized thread.
     * @param thisRef - is the reference to the class that contains the property
     * @param property - is an instance of the [KProperty] class, which contains metadata.
     * @return T - T or null.
     */
    open operator fun getValue(thisRef: Any?, property: KProperty<*>): T? {
        if (thisRef !is SharedPreferencesProvider)
            throw RuntimeException("Please check if your manager implementation class implement SharedPreferencesProvider interface.")

        synchronized(this) {
            if (!initialized) {
                variable = thisRef.preferences.all[key] as? T
                initialized = true
            }
            return variable as? T
        }
    }
}