Usage in activity or fragment: private var variableName by SharedString { requireContext() }

SharedString

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

class SharedString(private val context: () -> Context) : ReadWriteProperty<Any, String?> {

    private val sharedPreferences by lazy {
        with(context()) {
            getSharedPreferences("${javaClass.simpleName}_stored_vars", MODE_PRIVATE)
        }
    }

    override fun getValue(thisRef: Any, property: KProperty<*>): String? {
        return sharedPreferences.getString(property.name, "")
    }

    @SuppressLint("ApplySharedPref")
    override fun setValue(thisRef: Any, property: KProperty<*>, value: String?) {
        // write immediately
        sharedPreferences.edit().putString(property.name, value).commit()
    }

}