In this article, we will learn how to Save And Retrieve Class Object From Shared Preferences Using Gson Library in Kotlin. Many times, we need to save an instance of a class that has only fields like Int, Long, Float, Double, String, Boolean and objects of different classes.
We use the GSON library that helps us to convert the model class to JSON String and then save the JSON String into the SharedPreferences. We read that JSON String and convert it back to the object whenever you want to read it.
Dependency GSON Library
To add the GSON library, add the following dependency in your module-level build.gradle. The below line adds the GSON library to your project.
dependencies {
implementation 'com.google.code.gson:gson:2.8.6'
//Other dependencies of our project
}To keep the example simple, let’s add just four properties to our MyObject class
class User {
var myValue = 0
var myAge: String? = null
var myFirstName: String? = null
var myLastName: String? = null
}Simple Method to Store Class Object into Shared Preferences
val prefsEditor = appSharedPrefs.edit()
val gson = Gson()
val json = gson.toJson(obj)
prefsEditor.putString("MyObject", json)
prefsEditor.commit()
Add two buttons and four EditText fields in the XML file. Add the onClick command to the XML so when the button is pressed our methods are executed.
Store Class Object in the SharedPreferences Using GSON
In the MainActivity add the following method. This method will be called when you click on the Save button. It will create an instance of “MyObject” and set the “MyValue” string to whatever you type in the EditText inputEditText. Then it will convert the object to a string using the GSON library and store that string in the SharedPreferences.
fun storeButton_Clicked(v: View?) {
val inputFirstName =
findViewById<View>(R.id.inputFirstName) as EditText
val inputLastName =
findViewById<View>(R.id.inputLastName) as EditText
val inputAge =
findViewById<View>(R.id.inputAge) as EditText
val obj = MyObject()
obj.myValue = 2
obj.myFirstName = inputFirstName.text.toString()
obj.myLastName = inputLastName.text.toString()
obj.myAge = inputAge.text.toString()
val appSharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this.applicationContext)
val prefsEditor = appSharedPrefs.edit()
val gson = Gson()
val json = gson.toJson(obj)
prefsEditor.putString("MyObject", json)
prefsEditor.commit()
Toast.makeText(this, "Object stored in SharedPreferences", Toast.LENGTH_LONG)
}Get The Object From Shared Preferences
Now get the object from shared preferences and display it in the outputEditText.
fun getButton_Clicked(v: View?) {
val outputEditText =
findViewById<View>(R.id.outputEditText) as TextView
val appSharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this.applicationContext)
val gson = Gson()
val json = appSharedPrefs.getString("MyObject", "")
val obj = gson.fromJson(json, MyObject::class.java)
outputEditText.setText("obj.MyFirstName: [" + obj.myFirstName + "] obj.MyLastName: [" + obj.myLastName + "] obj.myAge: [" + obj.myAge + "] obj.MyValue: [" + obj.myValue + "]")
Toast.makeText(this, "Object fetch from SharedPreferences successfully", Toast.LENGTH_LONG)
}XML Code
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:background="#FFFFFF"
android:orientation="vertical">
<TextView
android:id="@+id/textDiplay"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_marginTop="24dp"
android:hint="Enter Name"
android:text="Store and Get an Object in Android Shared Preferences using GSON"
android:textAlignment="center"
android:textSize="24dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
</TextView>
<EditText
android:id="@+id/inputFirstName"
android:layout_width="353dp"
android:layout_height="wrap_content"
android:layout_below="@+id/textDiplay"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginTop="36dp"
android:hint="First Name"
android:text=""
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textDiplay">
</EditText>
<EditText
android:id="@+id/inputLastName"
android:layout_width="351dp"
android:layout_height="wrap_content"
android:layout_below="@+id/inputFirstName"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginTop="24dp"
android:hint="Last Name"
android:text=""
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/inputFirstName">
</EditText>
<EditText
android:id="@+id/inputAge"
android:layout_width="350dp"
android:layout_height="wrap_content"
android:layout_below="@+id/inputLastName"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginTop="28dp"
android:hint="Age"
android:text=""
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.54"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/inputLastName">
</EditText>
<Button
android:id="@+id/storeButton"
android:layout_width="222dp"
android:layout_height="52dp"
android:layout_below="@+id/inputAge"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginTop="20dp"
android:background="@color/design_default_color_primary"
android:onClick="storeButton_Clicked"
android:text="Save"
android:textColor="@color/white"
android:textSize="17dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.497"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/inputAge">
</Button>
<TextView
android:id="@+id/outputEditText"
android:layout_width="344dp"
android:layout_height="53dp"
android:layout_above="@+id/getButton"
android:layout_below="@+id/storeButton"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginTop="32dp"
android:hint="Get Data show here"
android:text=""
android:textSize="15dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.492"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/storeButton">
</TextView>
<Button
android:id="@+id/getButton"
android:layout_width="218dp"
android:layout_height="54dp"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_alignParentBottom="true"
android:background="@color/design_default_color_primary"
android:onClick="getButton_Clicked"
android:text="Get"
android:textColor="@color/white"
android:textSize="17dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="@+id/outputEditText"
app:layout_constraintStart_toStartOf="@+id/outputEditText"
app:layout_constraintTop_toBottomOf="@+id/outputEditText"
app:layout_constraintVertical_bias="0.47">
</Button>
</androidx.constraintlayout.widget.ConstraintLayout>
MyObject Class
package com.example.handyopinion_sharedpreferences_gson
class MyObject {
var myValue = 0
var myAge: String? = null
var myFirstName: String? = null
var myLastName: String? = null
}
Main Activity Class
package com.example.handyopinion_sharedpreferences_gson
import android.app.Activity
import android.os.Bundle
import android.preference.PreferenceManager
import android.view.View
import android.widget.EditText
import android.widget.TextView
import android.widget.Toast
import com.google.gson.Gson
import java.util.function.IntFunction
class MainActivity : Activity() {
/** Called when the activity is first created. */
public override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
fun storeButton_Clicked(v: View?) {
val inputFirstName =
findViewById<View>(R.id.inputFirstName) as EditText
val inputLastName =
findViewById<View>(R.id.inputLastName) as EditText
val inputAge =
findViewById<View>(R.id.inputAge) as EditText
val obj = MyObject()
obj.myValue = 2
obj.myFirstName = inputFirstName.text.toString()
obj.myLastName = inputLastName.text.toString()
obj.myAge = inputAge.text.toString()
val appSharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this.applicationContext)
val prefsEditor = appSharedPrefs.edit()
val gson = Gson()
val json = gson.toJson(obj)
prefsEditor.putString("MyObject", json)
prefsEditor.commit()
Toast.makeText(this, "Object stored in SharedPreferences", Toast.LENGTH_LONG)
}
fun getButton_Clicked(v: View?) {
val outputEditText =
findViewById<View>(R.id.outputEditText) as TextView
val appSharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this.applicationContext)
val gson = Gson()
val json = appSharedPrefs.getString("MyObject", "")
val obj = gson.fromJson(json, MyObject::class.java)
outputEditText.setText("obj.MyFirstName: [" + obj.myFirstName + "] obj.MyLastName: [" + obj.myLastName + "] obj.myAge: [" + obj.myAge + "] obj.MyValue: [" + obj.myValue + "]")
Toast.makeText(this, "Object fetch from SharedPreferences successfully", Toast.LENGTH_LONG)
}
}Run the program. Save an object and retrieve it from SharedPreferences. That’s it. This is how to Save And Retrieve Class Object From Shared Preferences Using Gson Library in Kotlin.
If you have any questions or suggestions, feel free to ask in the comments section below.
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How to Save And Get Data From Shared Preferences in Kotlin
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