Type safe SharedPreferences

TSSP.kt

package net.numa08.typesafesharedpreferences

import android.content.SharedPreferences

sealed class Key<T> {
    abstract val key: String

    object Address : Key<String>() {
        override val key: String = "address"
    }
}

class Wrapper(private val preferences: SharedPreferences) {

    fun <T> write(key: Key<T>, value: T) {
        val editor = preferences.edit()
        when (value) {
            is String -> editor.putString(key.key, value)
            // putXXX for float, int, long and StringSet
        }
        editor.apply()
    }

    fun <T> read(key: Key<T>, default: T? = null): T? {
        @Suppress("UNCHECKED_CAST")
        return preferences.all[key.key] as? T ?: default
    }

}

@Suppress("UNREACHABLE_CODE")
fun test() {
    val address = "Japan, Osaka"
    val wrapper = Wrapper(preferences = TODO())
    
    wrapper.write(Key.Address, address)
    
    val saved = wrapper.read(Key.Address)
}