Singleton SharedPreferences manager. Is based on general abstract class (SharedPreferenceWrapper) and a project-specific Singleton (ProjectPreferences)

ProjectPreferences.kt

import android.content.Context
import android.content.res.Resources
import androidx.preference.PreferenceManager
import org.albspazio.myproject.R
import org.albaspazio.core.sharedpreferences.SharedPreferenceWrapper

// this must be implemented for a specific project
object ProjectPreferences: SharedPreferenceWrapper() {

    // init values of each Preference are stored in a specific resource. associate them!
    private val keysHashMap:HashMap<String,Int> = hashMapOf(
        "propr1" to R.integer.pref_propr1,
        "propr2" to R.string.pref_propr2,)

    private lateinit var resources: Resources

    //call it once
    fun init(context:Context, pref_name:String="", mode:Int = Context.MODE_PRIVATE){

        if(isInitialized()) return      // prevent multiple init

        prefs = if(pref_name.isEmpty()) PreferenceManager.getDefaultSharedPreferences(context)
                else                    context.getSharedPreferences(pref_name, mode)

        resources = context.resources
        setDefault()
    }

    override fun read(key: String, value: Any): Any?{
        return  if(!keysHashMap.contains(key) || !isInitialized()) null
                else super.read(key, value)
    }

    override fun write(key: String, value: Any): Any?{
        return  if(!keysHashMap.contains(key) || !isInitialized())    null
                else super.write(key, value)
    }
    //==============================================================================================
    // if a preference key is still unset, init it taking values from resources
    private fun setDefault(){
        keysHashMap.map{

            if(!prefs.contains(it.key))
                when(it.key){
                    "pref_propr1" -> write(it.key, resources.getInteger(it.value).toString())
                    "pref_propr2" -> write(it.key, resources.getString(it.value))
                }
            it
        }
    }
    //==============================================================================================
}

SharedPreferenceWrapper.kt

package org.albaspazio.core.sharedpreferences

import android.content.SharedPreferences

// this class is project-independent. 
// can be defined in an external module/library
abstract class SharedPreferenceWrapper {

    protected lateinit var prefs: SharedPreferences

    fun isInitialized() = ::prefs.isInitialized

    open fun read(key: String, defvalue: Any): Any? {
        return when(defvalue){
            is String   -> prefs.getString(key, defvalue)
            is Int      -> prefs.getInt(key, defvalue)
            is Boolean  -> prefs.getBoolean(key, defvalue)
            is Long     -> prefs.getLong(key, defvalue)
            is Float    -> prefs.getFloat(key, defvalue)
            is Set<*>   -> {
                        if(defvalue.isNotEmpty() && defvalue.elementAt(0) is String)
                                prefs.getStringSet(key, defvalue as Set<String>)
                        else    return null
            }
            else        -> null
        }
    }

    open fun write(key: String, value: Any):Any? {
        val prefsEditor: SharedPreferences.Editor = prefs.edit()
        with(prefsEditor) {
            when(value){
                is String   -> putString(key, value)
                is Int      -> putInt(key, value)
                is Boolean  -> putBoolean(key, value)
                is Long     -> putLong(key, value)
                is Float    -> putFloat(key, value)
                is Set<*>   -> {
                                if(value.isNotEmpty() && value.elementAt(0) is String)    putStringSet(key, value as Set<String>)
                                else                                                            return null
                }
                else        -> return null
            }
            commit()
        }
        return value
    }
}