How can I save a HashMap to Sharedpreferences in Android Kotlin?

This example demonstrates how to save a HashMap to Sharedpreferences in Android Kotlin.

Step 1 − Create a new project in Android Studio, go to File ? New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

Example

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:id="@+id/rlMain"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:layout_margin="16dp"
   android:orientation="vertical">
   <EditText
      android:id="@+id/etName"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:hint="Name"
      android:inputType="text" />
   <EditText
      android:id="@+id/etAge"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:hint="Age"
      android:inputType="number" />
   <EditText
      android:id="@+id/etGame"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:hint="Favourite game"
      android:inputType="text" />
   <Button
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_marginTop="16dp"
      android:onClick="saveLocal"
      android:text="save local" />
   <TextView
      android:id="@+id/textView"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_marginTop="20dp"
      android:textColor="@android:color/background_dark"
      android:textSize="24sp"
      android:textStyle="bold|italic" />
</LinearLayout>

Step 3 − Add the following code to src/MainActivity.kt

Example

import android.content.Context
import android.content.SharedPreferences
import android.os.Bundle
import android.view.View
import android.widget.EditText
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import org.json.JSONObject
import java.util.*
import kotlin.collections.HashMap
class MainActivity : AppCompatActivity() {
   private val mapKey = "map"
   lateinit var etName: EditText
   lateinit var etAge: EditText
   lateinit var etGame: EditText
   lateinit var textView: TextView
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      textView = findViewById(R.id.textView)
      etName = findViewById(R.id.etName)
      etAge = findViewById(R.id.etAge)
      etGame = findViewById(R.id.etGame)
      val outputMap: Map<String, Any> = loadMap()
      if (outputMap.containsKey("name"))
      etName.setText(Objects.requireNonNull(outputMap["name"]).toString())
      if (outputMap.containsKey("age"))
      etAge.setText(Objects.requireNonNull(outputMap["age"]).toString())
      if (outputMap.containsKey("game"))
      etGame.setText(Objects.requireNonNull(outputMap["game"]).toString())
   }
   private fun loadMap(): Map<String, Any> {
      val outputMap: Map<String, Any> = HashMap()
      val pSharedPref = applicationContext.getSharedPreferences(
         "MyVariables", Context.MODE_PRIVATE
      )
      if (pSharedPref != null) {
         val jsonString = pSharedPref.getString(mapKey, JSONObject().toString())
         val jsonObject = JSONObject(jsonString)
         val keysItr = jsonObject.keys()
         while (keysItr.hasNext()) {
            val key = keysItr.next()
            outputMap[key]
         }
      }
      return outputMap
   }
   fun saveLocal(view: View) {
      val name = etName.text.toString().trim()
      val age = etAge.text.toString().trim()
      val game = etGame.text.toString().trim()
      when {
         name.isEmpty() -> {
            etName.error = "*required"
            etName.requestFocus()
         }
         age.isEmpty() -> {
            etAge.error = "*required"
            etAge.requestFocus()
         }
         game.isEmpty() -> {
            etGame.error = "*required"
            etGame.requestFocus()
         }
         else -> {
            val inputMap: MutableMap<String, Any> = HashMap()
            inputMap["name"] = name
            inputMap["age"] = age
            inputMap["game"] = game
            saveMap(inputMap)
            Toast.makeText(applicationContext, "Saved Locally!", Toast.LENGTH_SHORT).show()
            textView.text = inputMap.toString()
         }
      }
   }
   private fun saveMap(inputMap: MutableMap<String, Any>) {
      val sharedPreferences: SharedPreferences = applicationContext.getSharedPreferences(
         "MyVariables", Context.MODE_PRIVATE
      )
      val jsonObject = JSONObject(inputMap)
      val jsonString = jsonObject.toString()
      val editor: SharedPreferences.Editor = sharedPreferences.edit()
      editor.remove(mapKey).apply()
      editor.putString(mapKey, jsonString)
      editor.commit()
   }
}

Step 4 − Add the following code to androidManifest.xml

Example

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="app.com.myapplication">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen