Add Dialog to change theme.

app/src/main/java/me/zobrist/tichucounter/MainActivity.kt

@@ -1,5 +1,6 @@
 package me.zobrist.tichucounter
 
+import android.app.AlertDialog
 import android.os.Bundle
 import android.view.Menu
 import android.view.MenuItem
@@ -8,6 +9,7 @@ import androidx.core.widget.doOnTextChanged
 import kotlinx.android.synthetic.main.content_main.*
 import android.text.InputType
 import android.widget.ScrollView
+import androidx.appcompat.app.AppCompatDelegate
 
 class MainActivity : AppCompatActivity() {
 
@@ -256,6 +258,10 @@ class MainActivity : AppCompatActivity() {
                 undoLastRound()
                 true
             }
+            R.id.action_theme -> {
+                chooseThemeDialog()
+                true
+            }
             else -> super.onOptionsItemSelected(item)
         }
     }
@@ -317,4 +323,44 @@ class MainActivity : AppCompatActivity() {
         submit.isEnabled = false
     }
 
+
+    private fun chooseThemeDialog() {
+
+        val builder = AlertDialog.Builder(this)
+        builder.setTitle(getString(R.string.choose_theme_text))
+        val styles = arrayOf("Light","Dark","System default")
+
+        var checkedItem = when(AppCompatDelegate.getDefaultNightMode()) {
+            AppCompatDelegate.MODE_NIGHT_NO -> 0
+            AppCompatDelegate.MODE_NIGHT_YES -> 1
+            AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM -> 2
+            else -> -1
+        }
+
+
+        builder.setSingleChoiceItems(styles, checkedItem) { dialog, which ->
+
+            when (which) {
+                0 -> {
+                    AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
+                    delegate.applyDayNight()
+                    dialog.dismiss()
+                }
+                1 -> {
+                    AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES)
+                    delegate.applyDayNight()
+
+                    dialog.dismiss()
+                }
+                2 -> {
+                    AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM)
+                    delegate.applyDayNight()
+                    dialog.dismiss()
+                }
+            }
+        }
+
+        val dialog = builder.create()
+        dialog.show()
+    }
 }

app/src/main/res/menu/menu_main.xml

@@ -2,14 +2,19 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     tools:context="me.zobrist.tichucounter.MainActivity">
+    <item
+        android:id="@+id/action_undo"
+        android:icon="@android:drawable/ic_menu_revert"
+        android:orderInCategory="5"
+        android:title="@string/undo" />
     <item
         android:id="@+id/action_clear"
         android:checkable="false"
-        android:orderInCategory="100"
+        android:orderInCategory="10"
         android:title="@string/clear"
         app:showAsAction="never" />
     <item
-        android:id="@+id/action_undo"
-        android:icon="@android:drawable/ic_menu_revert"
-        android:title="@string/undo" />
+        android:id="@+id/action_theme"
+        android:orderInCategory="15"
+        android:title="@string/choose_theme_text" />
 </menu>

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

@@ -2,4 +2,5 @@
 <resources>
     <string name="clear">Neues Spiel Starten</string>
     <string name="undo">Letzte Runde Löschen</string>
+    <string name="choose_theme_text">Theme auswählen</string>
 </resources>

app/src/main/res/values-gsw-rCH/strings.xml

@@ -2,4 +2,5 @@
 <resources>
     <string name="clear">Neus Spil Starte</string>
     <string name="undo">Letschti Rundi Lösche</string>
+    <string name="choose_theme_text">Usgsehe ändere</string>
 </resources>

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

@@ -6,4 +6,5 @@
     <string name="team_b" translatable="false">Team B</string>
     <string name="clear">Start New Game</string>
     <string name="undo">Undo Last Round</string>
+    <string name="choose_theme_text">Choose theme</string>
 </resources>

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

@@ -1,10 +1,11 @@
 <resources>
     <!-- Base application theme. -->
-    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
+    <style name="AppTheme" parent="Theme.AppCompat.DayNight">
         <!-- 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.NoActionBar">