In this tutorial, we’ll learn how to implement SharedPreferences in our Android Application using Kotlin.
SharedPreferences is part of the Android API since API level 1. It’s an interface that allows us to store/modify/delete data locally. Generally, it is used to cache user local data such as login forms. The data is stored in the form of a key-value pair. You can create multiple files to hold the SharedPreferences data.
Let’s look at some important methods for SharedPreferences.
getSharedPreferences(String, int)
method is used to retrieve an instance of the SharedPreferences
. Here String
is the name of the SharedPreferences file and int
is the Context passed.SharedPreferences.Editor()
is used to edit values in the SharedPreferences
.commit()
or apply()
to save the values in the SharedPreferences file. The commit()
saves the values immediately whereas apply()
saves the values asynchronously.We can set values on our SharedPreference instance using Kotlin in the following way.
val sharedPreference = getSharedPreferences("PREFERENCE_NAME",Context.MODE_PRIVATE)
var editor = sharedPreference.edit()
editor.putString("username","Anupam")
editor.putLong("l",100L)
editor.commit()
For retrieving a value:
sharedPreference.getString("username","defaultName")
sharedPreference.getLong("l",1L)
The permitted types on a SharedPreference instance are:
We can also clear all the values or remove a particular value by calling clear()
and remove(String key)
methods.
editor.clear()
editor.remove("username")
Note: Changes made to the editor after the commit or apply aren’t considered. The above way to save and retrieve values from a SharedPreference is nearly the same as we do in Java. So where’s the magic of Kotlin? That’s what we’ll see next through an example android application.
In this application, we’ll have a login screen, which allows us to save/clear the form data.
The code for the activity_main.xml
layout file is given below.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<EditText
android:id="@+id/inUserId"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:hint="User ID"
android:inputType="number" />
<EditText
android:id="@+id/inPassword"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/inUserId"
android:hint="Password"
android:inputType="textPassword" />
<Button
android:id="@+id/btnSave"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/inPassword"
android:text="SAVE USER DATA" />
<Button
android:id="@+id/btnClear"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_below="@+id/btnSave"
android:text="CLEAR USER DATA" />
<Button
android:id="@+id/btnShow"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_below="@+id/inPassword"
android:text="SHOW" />
<Button
android:id="@+id/btnShowDefault"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_below="@+id/btnSave"
android:text="Show Default" />
</RelativeLayout>
The code for the MainActivity.kt
Kotlin class is given below.
package com.journaldev.androidlysharedpreferences
import android.content.Context
import android.content.SharedPreferences
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.preference.PreferenceManager
import android.view.View
import com.journaldev.androidlysharedpreferences.PreferenceHelper.defaultPreference
import com.journaldev.androidlysharedpreferences.PreferenceHelper.password
import com.journaldev.androidlysharedpreferences.PreferenceHelper.userId
import com.journaldev.androidlysharedpreferences.PreferenceHelper.clearValues
import com.journaldev.androidlysharedpreferences.PreferenceHelper.customPreference
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity(), View.OnClickListener {
val CUSTOM_PREF_NAME = "User_data"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
btnSave.setOnClickListener(this)
btnClear.setOnClickListener(this)
btnShow.setOnClickListener(this)
btnShowDefault.setOnClickListener(this)
}
override fun onClick(v: View?) {
val prefs = customPreference(this, CUSTOM_PREF_NAME)
when (v?.id) {
R.id.btnSave -> {
prefs.password = inPassword.text.toString()
prefs.userId = inUserId.text.toString().toInt()
}
R.id.btnClear -> {
prefs.clearValues
}
R.id.btnShow -> {
inUserId.setText(prefs.userId.toString())
inPassword.setText(prefs.password)
}
R.id.btnShowDefault -> {
val defaultPrefs = defaultPreference(this)
inUserId.setText(defaultPrefs.userId.toString())
inPassword.setText(defaultPrefs.password)
}
}
}
}
object PreferenceHelper {
val USER_ID = "USER_ID"
val USER_PASSWORD = "PASSWORD"
fun defaultPreference(context: Context): SharedPreferences = PreferenceManager.getDefaultSharedPreferences(context)
fun customPreference(context: Context, name: String): SharedPreferences = context.getSharedPreferences(name, Context.MODE_PRIVATE)
inline fun SharedPreferences.editMe(operation: (SharedPreferences.Editor) -> Unit) {
val editMe = edit()
operation(editMe)
editMe.apply()
}
var SharedPreferences.userId
get() = getInt(USER_ID, 0)
set(value) {
editMe {
it.putInt(USER_ID, value)
}
}
var SharedPreferences.password
get() = getString(USER_PASSWORD, "")
set(value) {
editMe {
it.putString(USER_PASSWORD, value)
}
}
var SharedPreferences.clearValues
get() = { }
set(value) {
editMe {
it.clear()
}
}
}
Thanks to Kotlin Android Extensions, we don’t have to use findViewById for each XML view. In the above code, we are creating a singleton class using the object
keyword. We are declaring an inline higher-order function named editMe(), which holds the logic for the edit operation. We’ve created separate properties for each of the values. We are using the get and set Kotlin properties to retrieve and set the data in the shared preferences. Kotlin has reduced the code verbosity and it looks much cleaner. Furthermore, we can make it more concise by using another Kotlin higher-order function shown below.
fun SharedPreferences.Editor.put(pair: Pair<String, Any>) {
val key = pair.first
val value = pair.second
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)
else -> error("Only primitive types can be stored in SharedPreferences")
}
And we do the following while setting the values:
var SharedPreferences.password
get() = getString(USER_PASSWORD, "")
set(value) {
editMe {
it.put(USER_PASSWORD to value)
}
}
This is as close as Kotlin can get you to the English Language. The output of the above application in action is given below.
You can download the source code from the following link: AndroidlySharedPreferences
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Hello, I am interested in your implementation of a SharedPreference Util, but when I try to write it myself, I found that kotlin make the value in set(value) a ? type, so I have to make the put method from Pair to Pair, that seems not convenient at all, I guess kotlin update it’s grammar, so how can I implement this object PreferenceHelper now? Thanks.
- Daniel
how to define preference inside fragment?
- Ayush Pandey