handle Toggle favorite icon updating

app/src/main/kotlin/com/simplemobiletools/gallery/activities/ViewPagerActivity.kt

@@ -283,6 +283,8 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
             findItem(R.id.menu_save_as).isVisible = mRotationDegrees != 0
             findItem(R.id.menu_hide).isVisible = !currentMedium.name.startsWith('.')
             findItem(R.id.menu_unhide).isVisible = currentMedium.name.startsWith('.')
+            findItem(R.id.menu_add_to_favorites).isVisible = !currentMedium.isFavorite && !config.bottomActions
+            findItem(R.id.menu_remove_from_favorites).isVisible = currentMedium.isFavorite && !config.bottomActions
             findItem(R.id.menu_lock_orientation).isVisible = mRotationDegrees == 0
             findItem(R.id.menu_lock_orientation).title = getString(if (mIsOrientationLocked) R.string.unlock_orientation else R.string.lock_orientation)
             findItem(R.id.menu_rotate).setShowAsAction(
@@ -293,6 +295,9 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
                     })
         }
 
+        if (config.bottomActions) {
+            updateFavoriteIcon(currentMedium)
+        }
         return true
     }
 
@@ -316,6 +321,8 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
             R.id.menu_show_on_map -> showOnMap()
             R.id.menu_rotate_right -> rotateImage(90)
             R.id.menu_rotate_left -> rotateImage(270)
+            R.id.menu_add_to_favorites -> toggleFavorite()
+            R.id.menu_remove_from_favorites -> toggleFavorite()
             R.id.menu_rotate_one_eighty -> rotateImage(180)
             R.id.menu_lock_orientation -> toggleLockOrientation()
             R.id.menu_save_as -> saveImageAs()
@@ -746,7 +753,7 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
 
     private fun initBottomActionButtons() {
         bottom_favorite.setOnClickListener {
-
+            toggleFavorite()
         }
 
         bottom_edit.setOnClickListener {
@@ -762,6 +769,16 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
         }
     }
 
+    private fun updateFavoriteIcon(medium: Medium) {
+        val icon = if (medium.isFavorite) R.drawable.ic_star_on else R.drawable.ic_star_off
+        bottom_favorite.setImageResource(icon)
+    }
+
+    private fun toggleFavorite() {
+        getCurrentMedium()!!.isFavorite = !getCurrentMedium()!!.isFavorite
+        invalidateOptionsMenu()
+    }
+
     override fun onActivityResult(requestCode: Int, resultCode: Int, resultData: Intent?) {
         if (requestCode == REQUEST_EDIT_IMAGE) {
             if (resultCode == Activity.RESULT_OK && resultData != null) {
@@ -972,7 +989,7 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
             mPos = position
             updateActionbarTitle()
             mRotationDegrees = 0
-            supportInvalidateOptionsMenu()
+            invalidateOptionsMenu()
             scheduleSwipe()
         }
     }

app/src/main/kotlin/com/simplemobiletools/gallery/models/Medium.kt

@@ -26,7 +26,7 @@ data class Medium(
         @ColumnInfo(name = "date_taken") var taken: Long,
         @ColumnInfo(name = "size") val size: Long,
         @ColumnInfo(name = "type") val type: Int,
-        @ColumnInfo(name = "is_favorite") val isFavorite: Boolean) : Serializable {
+        @ColumnInfo(name = "is_favorite") var isFavorite: Boolean) : Serializable {
 
     companion object {
         private const val serialVersionUID = -6553149366975455L

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

@@ -34,6 +34,16 @@
                 android:title="@string/rotate_one_eighty"/>
         </menu>
     </item>
+    <item
+        android:id="@+id/menu_add_to_favorites"
+        android:icon="@drawable/ic_star_off"
+        android:title="@string/add_to_favorites"
+        app:showAsAction="ifRoom"/>
+    <item
+        android:id="@+id/menu_remove_from_favorites"
+        android:icon="@drawable/ic_star_on"
+        android:title="@string/remove_from_favorites"
+        app:showAsAction="ifRoom"/>
     <item
         android:id="@+id/menu_lock_orientation"
         android:title="@string/lock_orientation"