Hide dark theme on devices older than Q

Most likely, the don't support it (although theoratically, the -night
resource qualifier has been around for a while).

Change-Id: I54f736c2b06c71bb520727b0c834e687cad09237

vector/src/main/java/im/vector/app/features/settings/VectorSettingsPreferencesFragment.kt

@@ -52,8 +52,9 @@ class VectorSettingsPreferencesFragment @Inject constructor(
         setUserInterfacePreferences()
 
         // Themes
-        findPreference<VectorListPreference>(ThemeUtils.APPLICATION_THEME_KEY)!!
-                .onPreferenceChangeListener = Preference.OnPreferenceChangeListener { _, newValue ->
+        val lightThemePref = findPreference<VectorListPreference>(ThemeUtils.APPLICATION_THEME_KEY)!!
+        val darkThemePref = findPreference<VectorListPreference>(ThemeUtils.APPLICATION_DARK_THEME_KEY)!!
+        lightThemePref.onPreferenceChangeListener = Preference.OnPreferenceChangeListener { _, newValue ->
             if (newValue is String) {
                 ThemeUtils.setApplicationLightTheme(requireContext().applicationContext, newValue)
                 // Restart the Activity
@@ -63,21 +64,27 @@ class VectorSettingsPreferencesFragment @Inject constructor(
                 false
             }
         }
-        findPreference<VectorListPreference>(ThemeUtils.APPLICATION_DARK_THEME_KEY)!!
-                .onPreferenceChangeListener = Preference.OnPreferenceChangeListener { _, newValue ->
-            if (newValue is String) {
-                ThemeUtils.setApplicationDarkTheme(requireContext().applicationContext, newValue)
-                // Restart the Activity
-                activity?.let {
-                    // Note: recreate does not apply the color correctly
-                    it.startActivity(it.intent)
-                    it.finish()
+        if (ThemeUtils.darkThemePossible()) {
+            lightThemePref.title = getString(R.string.settings_light_theme)
+            darkThemePref.onPreferenceChangeListener = Preference.OnPreferenceChangeListener { _, newValue ->
+                if (newValue is String) {
+                    ThemeUtils.setApplicationDarkTheme(requireContext().applicationContext, newValue)
+                    // Restart the Activity
+                    activity?.let {
+                        // Note: recreate does not apply the color correctly
+                        it.startActivity(it.intent)
+                        it.finish()
+                    }
+                    true
+                } else {
+                    false
                 }
-                true
-            } else {
-                false
             }
+        } else {
+            lightThemePref.title = getString(R.string.settings_theme)
+            darkThemePref.parent?.removePreference(darkThemePref)
         }
+
         findPreference<VectorListPreference>(BubbleThemeUtils.BUBBLE_STYLE_KEY)!!
                 .onPreferenceChangeListener = Preference.OnPreferenceChangeListener { _, _ ->
             BubbleThemeUtils.invalidateBubbleStyle()

vector/src/main/java/im/vector/app/features/themes/ThemeUtils.kt

@@ -20,6 +20,7 @@ import android.app.Activity
 import android.content.Context
 import android.content.res.Configuration
 import android.graphics.drawable.Drawable
+import android.os.Build
 import android.util.TypedValue
 import android.view.Menu
 import androidx.annotation.AttrRes
@@ -55,7 +56,18 @@ object ThemeUtils {
     private var mUseDarkTheme = false
     private var mThemeInitialized = false
 
+    /**
+     * @return Whether a system-wide dark mode is available on this device
+     */
+    fun darkThemePossible(): Boolean {
+        // Available since Android 10: https://developer.android.com/guide/topics/ui/look-and-feel/darktheme
+        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q
+    }
+
     fun shouldUseDarkTheme(context: Context): Boolean {
+        if (!darkThemePossible()) {
+            return false
+        }
         val currentNightMode = context.resources.configuration.uiMode and Configuration.UI_MODE_NIGHT_MASK
         return currentNightMode == Configuration.UI_MODE_NIGHT_YES
     }

vector/src/main/res/values-de/strings_sc.xml

@@ -9,7 +9,8 @@
     <string name="settings_room_unread_kind_content">Verstecke Teilnehmerveränderungen</string>
     <string name="settings_room_unread_kind_original_content">Verstecke Teilnehmerveränderungen und Reaktionen</string>
 
-    <string name="settings_dark_theme">Nacht-Design</string>
+    <string name="settings_light_theme">Helles Design</string>
+    <string name="settings_dark_theme">Dunkles Design</string>
     <string name="sc_light_theme">SC Hell</string>
     <string name="sc_theme">SC Schwarz</string>
     <string name="sc_dark_theme">SC Dunkel</string>

vector/src/main/res/values/strings_sc.xml

@@ -9,7 +9,8 @@
     <string name="settings_room_unread_kind_content">Hide member changes</string>
     <string name="settings_room_unread_kind_original_content">Hide member changes and reactions</string>
 
-    <string name="settings_dark_theme">Night Theme</string>
+    <string name="settings_light_theme">Light theme</string>
+    <string name="settings_dark_theme">Dark theme</string>
     <string name="sc_light_theme">SC Light</string>
     <string name="sc_theme">SC Black</string>
     <string name="sc_dark_theme">SC Dark</string>