Android SharedPreferences – In this one article, We’ll learn the best practices of SharedPreferences in Android (Kotlin). I’ll show you, how we can store and retrieve values in SharedPreferences. For better understanding, I’ll create an android SharedPreferences example (Sample app) and take an example of Writing and Reading Values in SharedPreferences. So let started
What are SharedPreferences?
SharedPreferences is an android API that stores app data using key-value pairs and provides simple methods to read and write them.
Android system provides several options for you to save your data. These options are App-specific storage, Shared storage, Preferences, Databases. SharedPreferences comes in Preference. It offers a framework to save private, primitive data in key-value pairs.
Why SharedPreferences?
They’re mostly used to store user states when it comes to user settings or keeps a piece of small information(User details etc.) without needing storage permission. As per my opinion, you should store small primitive value in Preferences such as booleans, ints, longs, floats, and strings.
To better understand it, you can see in the following article here
Read More : RecycleView Click Listener (Kotlin)
Android SharedPreferences Example in Kotlin
1. Create new android application project
Let take an example for Android SharedPreferences , open android studio, and create a new project. Now create a interface named is IPreferenceHelper. In this Interface we are defining some getter setter for storing or retrieving preference value. such as ApiKey and UserId etc.
package com.sharedpreferencesexample
interface IPreferenceHelper {
fun setApiKey(apiKey: String)
fun getApiKey(): String
fun setUserId(userId: String)
fun getUserId(): String
fun clearPrefs()
}2. Create a singleton class for managing Preferences
Ideally SharedPreferences store the app level value, So the SharedPreferences instance should be single threw out the app. It should be a singleton. Let create a Singletone class named is PreferenceManager and implement IPreferenceHelper. Just like below
open class PreferenceManager constructor(context: Context) : IPreferenceHelper {
private val PREFS_NAME = "SharedPreferenceDemo"
private var preferences: SharedPreferences
init {
preferences = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE)
}
override fun setApiKey(apiKey: String) {
preferences[API_KEY] = apiKey
}
override fun getApiKey(): String {
return preferences[API_KEY] ?: ""
}
override fun setUserId(userId: String) {
preferences[USER_ID] = userId
}
override fun getUserId(): String {
return preferences[USER_ID] ?: ""
}
override fun clearPrefs() {
preferences.edit().clear().apply()
}
companion object {
const val API_KEY = "api_key"
const val USER_ID = "user_id"
}
}3. Write into your SharedPreferences
Normally, writing into SharedPreferences is simple. But I’m going to write a Kotlin extension, This extension is make writing very simple and reduce boilerplate code.
/**
* SharedPreferences extension function, to listen the edit() and apply() fun calls
* on every SharedPreferences operation.
*/
private inline fun SharedPreferences.edit(operation: (SharedPreferences.Editor) -> Unit) {
val editor = this.edit()
operation(editor)
editor.apply()
}
/**
* puts a key value pair in shared prefs if doesn't exists, otherwise updates value on given [key]
*/
private operator fun SharedPreferences.set(key: String, value: Any?) {
when (value) {
is String? -> edit { it.putString(key, value) }
is Int -> edit { it.putInt(key, value) }
is Boolean -> edit { it.putBoolean(key, value) }
is Float -> edit { it.putFloat(key, value) }
is Long -> edit { it.putLong(key, value) }
else -> throw UnsupportedOperationException("Not yet implemented")
}
}4. Read from SharedPreferences
Reading a value from SharedPreferences is also straightforward. I’m going to write another useful extension that provides more control over retrieving a value from SharedPreferences. Let check below code
/**
* finds value on given key.
* [T] is the type of value
* @param defaultValue optional default value - will take null for strings, false for bool and -1 for numeric values if [defaultValue] is not specified
*/
private inline operator fun <reified T : Any> SharedPreferences.get(
key: String,
defaultValue: T? = null
): T? {
return when (T::class) {
String::class -> getString(key, defaultValue as? String) as T?
Int::class -> getInt(key, defaultValue as? Int ?: -1) as T?
Boolean::class -> getBoolean(key, defaultValue as? Boolean ?: false) as T?
Float::class -> getFloat(key, defaultValue as? Float ?: -1f) as T?
Long::class -> getLong(key, defaultValue as? Long ?: -1) as T?
else -> throw UnsupportedOperationException("Not yet implemented")
}
}5. Finally your PreferenceManager class look like below
package com.sharedpreferencesexample
import android.content.Context
import android.content.SharedPreferences
open class PreferenceManager constructor(context: Context) : IPreferenceHelper {
private val PREFS_NAME = "SharedPreferenceDemo"
private var preferences: SharedPreferences
init {
preferences = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE)
}
override fun setApiKey(apiKey: String) {
preferences[API_KEY] = apiKey
}
override fun getApiKey(): String {
return preferences[API_KEY] ?: ""
}
override fun setUserId(userId: String) {
preferences[USER_ID] = userId
}
override fun getUserId(): String {
return preferences[USER_ID] ?: ""
}
override fun clearPrefs() {
preferences.edit().clear().apply()
}
companion object {
const val API_KEY = "api_key"
const val USER_ID = "user_id"
}
}
/**
* SharedPreferences extension function, to listen the edit() and apply() fun calls
* on every SharedPreferences operation.
*/
private inline fun SharedPreferences.edit(operation: (SharedPreferences.Editor) -> Unit) {
val editor = this.edit()
operation(editor)
editor.apply()
}
/**
* puts a key value pair in shared prefs if doesn't exists, otherwise updates value on given [key]
*/
private operator fun SharedPreferences.set(key: String, value: Any?) {
when (value) {
is String? -> edit { it.putString(key, value) }
is Int -> edit { it.putInt(key, value) }
is Boolean -> edit { it.putBoolean(key, value) }
is Float -> edit { it.putFloat(key, value) }
is Long -> edit { it.putLong(key, value) }
else -> throw UnsupportedOperationException("Not yet implemented")
}
}
/**
* finds value on given key.
* [T] is the type of value
* @param defaultValue optional default value - will take null for strings, false for bool and -1 for numeric values if [defaultValue] is not specified
*/
private inline operator fun <reified T : Any> SharedPreferences.get(
key: String,
defaultValue: T? = null
): T? {
return when (T::class) {
String::class -> getString(key, defaultValue as? String) as T?
Int::class -> getInt(key, defaultValue as? Int ?: -1) as T?
Boolean::class -> getBoolean(key, defaultValue as? Boolean ?: false) as T?
Float::class -> getFloat(key, defaultValue as? Float ?: -1f) as T?
Long::class -> getLong(key, defaultValue as? Long ?: -1) as T?
else -> throw UnsupportedOperationException("Not yet implemented")
}
}6. Access PreferenceManager into your presentation layers
Yes, Now your PreferenceManager class is ready for use. You can initialize PreferenceManager class into your ViewModel and Activity/Fragment, Make sure the context should be applicationContext.
7.Open the activity_main.xml and paste below code.
For making interesting example I have added two edit text and one button in this layout
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp"
tools:context=".MainActivity">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="Hello World!" />
<EditText
android:id="@+id/editText"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="textPersonName"
android:text="User Id"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="@+id/editText2"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:ems="10"
android:inputType="textPersonName"
android:text="API Key"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/editText" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="32dp"
android:text="Show Preference Data"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/editText2" />
</androidx.constraintlayout.widget.ConstraintLayout>8. Let access PreferenceManager class in your source file
Let’s check the below code This way you can easily read and write the value in SharePreferences
package com.sharedpreferencesexample
import android.annotation.SuppressLint
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
private val preferenceHelper: IPreferenceHelper by lazy { PreferenceManager(applicationContext) }
@SuppressLint("SetTextI18n")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// display saved data
textView.text =
" API Key - > ${preferenceHelper.getApiKey()} \n User Id -> ${preferenceHelper.getUserId()}"
button.setOnClickListener {
// Update data in SharedPreference
preferenceHelper.setApiKey(editText.text.toString())
preferenceHelper.setUserId(editText2.text.toString())
// display saved data
textView.text =
" API Key - > ${preferenceHelper.getApiKey()} \n User Id -> ${preferenceHelper.getUserId()}"
}
}
}7. Build & Test
Let run the app, in a movement your app will up and run, Now enter few value these EditText and click button. The value will display on TextView. This way you can read and write small amount of data in key-value pairs!
Conclusion
In this android SharedPreferences example, we’ll learn how we can save and retrieve value in SharedPreferences. I try to follow best practices for android development. Still, you want to improve… Very Welcome
