SharedPreferences — Complete Guide

// Calling commit on the main thread — blocks!
prefs.edit().putString("key", "value").commit()

// Creating multiple Editor instances
val editor1 = prefs.edit()
editor1.putString("key1", "value1")
editor1.apply()

val editor2 = prefs.edit() // New editor — key1 might not be written yet
editor2.putString("key2", "value2")
editor2.apply()

class PreferencesManager(context: Context) {
    private val prefs = context.getSharedPreferences("app_prefs", Context.MODE_PRIVATE)

    // Use apply() for async writes
    fun saveString(key: String, value: String) {
        prefs.edit().putString(key, value).apply() // Async, non-blocking
    }

    // Use commit() only when you need a synchronous result
    fun saveStringSync(key: String, value: String): Boolean {
        return prefs.edit().putString(key, value).commit() // Returns success
    }

    fun getString(key: String, default: String = ""): String {
        return prefs.getString(key, default) ?: default
    }

    // Don't use SharedPreferences for large data
    fun saveUser(user: User) {
        // WRONG: serializing large objects to SharedPreferences
        val json = Gson().toJson(user)
        prefs.edit().putString("user_data", json).apply()
        // Use Room or DataStore instead
    }

    // Batch multiple edits
    fun saveMultiple(key1: String, v1: String, key2: String, v2: Int) {
        prefs.edit().run {
            putString(key1, v1)
            putInt(key2, v2)
            apply() // Single disk write for all changes
        }
    }

    // Remove
    fun remove(key: String) {
        prefs.edit().remove(key).apply()
    }

    // Clear all
    fun clear() {
        prefs.edit().clear().apply()
    }

    // Migration to DataStore
    // Prefer DataStore for new code
}

// Using this from Compose
@Composable
fun RememberPreference(prefsManager: PreferencesManager) {
    var name by remember { mutableStateOf(prefsManager.getString("name")) }
    // Note: doesn't react to changes from other sources
}