Add day/night theme spinner in SettingsActivity along with a very basic implementation of its behavior.

app/src/main/java/cy/agorise/bitsybitshareswallet/activities/SettingsActivity.kt

@@ -1,8 +1,12 @@
 package cy.agorise.bitsybitshareswallet.activities
 
 import android.os.Bundle
+import android.preference.PreferenceManager
 import android.view.MenuItem
 import android.support.v7.app.AppCompatActivity
+import cy.agorise.bitsybitshareswallet.R
+import cy.agorise.bitsybitshareswallet.utils.Constants
+import kotlinx.android.synthetic.main.activity_settings.*
 
 /**
  * A simple activity for the user to select his preferences
@@ -11,7 +15,20 @@ class SettingsActivity : AppCompatActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
+
+        // TODO move the below to a BaseActivity to apply it to all activities
+        // Sets the theme to night mode if it has been selected by the user
+        if (PreferenceManager.getDefaultSharedPreferences(this)
+                .getBoolean(Constants.KEY_NIGHT_MODE_ACTIVATED, false)
+        ) {
+            setTheme(R.style.AppTheme_Dark)
+        }
+
+        setContentView(R.layout.activity_settings)
+
         setupActionBar()
+
+        initNightModeSwitch()
     }
 
     /**
@@ -21,6 +38,22 @@ class SettingsActivity : AppCompatActivity() {
         supportActionBar?.setDisplayHomeAsUpEnabled(true)
     }
 
+    private fun initNightModeSwitch() {
+        val nightModeOn = PreferenceManager.getDefaultSharedPreferences(this)
+            .getBoolean(Constants.KEY_NIGHT_MODE_ACTIVATED, false)
+
+        switchNightMode.isChecked = nightModeOn
+
+        switchNightMode.setOnCheckedChangeListener { buttonView, isChecked ->
+
+            PreferenceManager.getDefaultSharedPreferences(buttonView.context).edit()
+                    .putBoolean(Constants.KEY_NIGHT_MODE_ACTIVATED, isChecked).apply()
+
+            // Recreates the activity to apply the selected theme
+            this.recreate()
+        }
+    }
+
     override fun onOptionsItemSelected(item: MenuItem): Boolean {
         if (item.itemId == android.R.id.home) {
             onBackPressed()

app/src/main/java/cy/agorise/bitsybitshareswallet/utils/Constants.java

@@ -0,0 +1,8 @@
+package cy.agorise.bitsybitshareswallet.utils;
+
+public class Constants {
+    /**
+     * Key used to store the night mode setting into the shared preferences
+     */
+    public static final String KEY_NIGHT_MODE_ACTIVATED = "key_night_mode_activated";
+}

app/src/main/res/layout/activity_settings.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    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"
+    android:orientation="vertical"
+    android:paddingStart="@dimen/activity_horizontal_margin"
+    android:paddingEnd="@dimen/activity_horizontal_margin"
+    android:paddingTop="@dimen/activity_vertical_margin"
+    android:paddingBottom="32dp"
+    tools:context=".activities.SettingsActivity">
+
+    <Switch
+        android:id="@+id/switchNightMode"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/night_mode"
+        android:textAppearance="@style/TextAppearance.Body1"
+        android:textColor="?android:textColorPrimary"/>
+
+</LinearLayout>

app/src/main/res/values/strings.xml

@@ -8,4 +8,5 @@
 
     <!-- Settings -->
     <string name="title_settings">Settings</string>
+    <string name="night_mode">Night mode</string>
 </resources>

app/src/main/res/values/styles.xml

@@ -1,6 +1,6 @@
 <resources>
 
-    <!-- Base application theme. -->
+    <!-- Base application light theme. -->
     <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
         <!-- Customize your theme here. -->
         <item name="colorPrimary">@color/colorPrimary</item>
@@ -12,6 +12,22 @@
         <item name="windowNoTitle">true</item>
     </style>
     <style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar"/>
-    <style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light"/>
 
+    <!-- Base application dark theme. -->
+    <style name="AppTheme.Dark" parent="Theme.AppCompat">
+        <!-- Customize your theme here. -->
+        <item name="colorPrimary">@color/colorPrimary</item>
+        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
+        <item name="colorAccent">@color/colorAccent</item>
+    </style>
+    <style name="AppTheme.Dark.NoActionBar">
+        <item name="windowActionBar">false</item>
+        <item name="windowNoTitle">true</item>
+    </style>
+
+    <!-- Text styles -->
+    <style name="TextAppearance.Body1" parent="TextAppearance.AppCompat.Body1" >
+        <item name="android:textSize">16sp</item>
+    </style>
+    <style name="TextAppearance.Body2" parent="Base.TextAppearance.AppCompat.Body2" />
 </resources>