fix(ui): hacky fix for updating colors on pure black setting change

This is to avoid restarting the app to see the resulting color change,
when changing the pure black setting.

It'll be good to call `finish()` on the settings activity,
to avoid stacking activities every time the setting is changed.

uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/list/ListHabitsActivity.kt

@@ -79,6 +79,10 @@ class ListHabitsActivity : AppCompatActivity(), Preferences.Listener {
         menu.behavior.onPreferencesChanged()
     }
 
+    override fun onPureBlackChanged() {
+        screen.applyTheme()
+    }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 

uhabits-android/src/main/java/org/isoron/uhabits/preferences/SharedPreferencesStorage.kt

@@ -90,9 +90,10 @@ class SharedPreferencesStorage
                 preferences.isMidnightDelayEnabled = getBoolean(key, false)
             "pref_sticky_notifications" ->
                 preferences.setNotificationsSticky(getBoolean(key, false))
-            "pref_unknown_enabled" -> {
+            "pref_unknown_enabled" ->
                 preferences.areQuestionMarksEnabled = getBoolean(key, false)
-            }
+            "pref_pure_black" ->
+                preferences.isPureBlackEnabled = getBoolean(key, false)
         }
         sharedPreferences.registerOnSharedPreferenceChangeListener(this)
     }

uhabits-core/src/jvmMain/java/org/isoron/uhabits/core/preferences/Preferences.kt

@@ -128,6 +128,7 @@ open class Preferences(private val storage: Storage) {
         get() = storage.getBoolean("pref_pure_black", false)
         set(enabled) {
             storage.putBoolean("pref_pure_black", enabled)
+            for (l in listeners) l.onPureBlackChanged()
         }
     var isShortToggleEnabled: Boolean
         get() = storage.getBoolean("pref_short_toggle", false)
@@ -243,6 +244,7 @@ open class Preferences(private val storage: Storage) {
         fun onCheckmarkSequenceChanged() {}
         fun onNotificationsChanged() {}
         fun onQuestionMarksChanged() {}
+        fun onPureBlackChanged() {}
     }
 
     interface Storage {