Finished App

PrefDataStore/app/build.gradle

@@ -51,4 +51,8 @@ dependencies {
     //navigation
     implementation "androidx.navigation:navigation-fragment-ktx:2.4.1"
     implementation "androidx.navigation:navigation-ui-ktx:2.4.1"
+
+    //data-store
+    implementation "androidx.datastore:datastore-preferences:1.0.0"
+    implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.4.1"
 }

PrefDataStore/app/src/main/java/com/example/prefdatastore/LetterListFragment.kt

@@ -4,13 +4,19 @@ import android.os.Bundle
 import android.view.*
 import androidx.core.content.ContextCompat
 import androidx.fragment.app.Fragment
+import androidx.lifecycle.asLiveData
+import androidx.lifecycle.lifecycleScope
 import androidx.recyclerview.widget.GridLayoutManager
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
+import com.example.prefdatastore.data.SettingsDataStore
 import com.example.prefdatastore.databinding.FragmentLetterListBinding
+import kotlinx.coroutines.launch
 
 
 class LetterListFragment : Fragment() {
+
+    private lateinit var settingsDataStore: SettingsDataStore
     private var _binding: FragmentLetterListBinding? = null
 
     // This property is only valid between onCreateView and
@@ -39,6 +45,15 @@ class LetterListFragment : Fragment() {
         // Sets the LayoutManager of the recyclerview
         // On the first run of the app, it will be LinearLayoutManager
         chooseLayout()
+
+        settingsDataStore = SettingsDataStore(requireContext())
+
+        //convert the preferenceFlow to Livedata using asLiveData().
+        // Attach an observer and pass in the viewLifecycleOwner as the owner.
+        settingsDataStore.preferenceFlow.asLiveData().observe(viewLifecycleOwner) {
+            isLinearLayoutManager = it
+            chooseLayout()
+        }
     }
 
     override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
@@ -80,6 +95,11 @@ class LetterListFragment : Fragment() {
             R.id.action_switch_layout -> {
                 // Sets isLinearLayoutManager (a Boolean) to the opposite value
                 isLinearLayoutManager = !isLinearLayoutManager
+
+                // Launch a coroutine and write the layout setting in the preference Datastore
+                lifecycleScope.launch {
+                    settingsDataStore.saveLayoutToPreferencesStore(isLinearLayoutManager, requireContext())
+                }
                 // Sets layout and icon
                 chooseLayout()
                 setIcon(item)
@@ -102,5 +122,4 @@ class LetterListFragment : Fragment() {
         super.onDestroyView()
         _binding = null
     }
-
 }

PrefDataStore/app/src/main/java/com/example/prefdatastore/data/SettingsDataStore.kt

@@ -0,0 +1,45 @@
+package com.example.prefdatastore.data
+
+import android.content.Context
+import androidx.datastore.core.DataStore
+import androidx.datastore.preferences.core.Preferences
+import androidx.datastore.preferences.core.booleanPreferencesKey
+import androidx.datastore.preferences.core.edit
+import androidx.datastore.preferences.core.emptyPreferences
+import androidx.datastore.preferences.preferencesDataStore
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.catch
+import java.io.IOException
+
+
+private const val LAYOUT_PREFERENCES_NAME = "layout_preferences"
+
+private val Context.dataStore : DataStore<Preferences> by preferencesDataStore(
+    name = LAYOUT_PREFERENCES_NAME
+)
+
+class SettingsDataStore(context:Context) {
+    private val IS_LINEAR_LAYOUT_MANAGER = booleanPreferencesKey("is_linear_layout_manager")
+
+    val preferenceFlow: Flow<Boolean> = context.dataStore.data
+        .catch {
+            if (it is IOException) {
+                it.printStackTrace()
+                emit(emptyPreferences())
+            } else {
+                throw it
+            }
+        }
+        .map { preferences ->
+            // On the first run of the app, we will use LinearLayoutManager by default
+            preferences[IS_LINEAR_LAYOUT_MANAGER] ?: true
+        }
+
+    suspend fun saveLayoutToPreferencesStore(isLinearLayoutManager: Boolean, context: Context){
+        //call dataStore.edit(), and pass in a block of code to store the new value.
+        context.dataStore.edit { preferences->
+            preferences[IS_LINEAR_LAYOUT_MANAGER] = isLinearLayoutManager
+        }
+    }
+}