make sure item group section titles span across the whole line

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

@@ -325,6 +325,7 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
                 setupZoomListener(mZoomListener)
                 media_grid.adapter = this
             }
+            setupLayoutManager()
         } else {
             (currAdapter as MediaAdapter).updateMedia(media)
         }
@@ -553,6 +554,16 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
         }
 
         layoutManager.spanCount = config.mediaColumnCnt
+        val adapter = getMediaAdapter()
+        layoutManager.spanSizeLookup = object : GridLayoutManager.SpanSizeLookup() {
+            override fun getSpanSize(position: Int): Int {
+                return if (adapter?.isASectionTitle(position) == true) {
+                    layoutManager.spanCount
+                } else {
+                    1
+                }
+            }
+        }
     }
 
     private fun initZoomListener() {

app/src/main/kotlin/com/simplemobiletools/gallery/adapters/MediaAdapter.kt

@@ -160,6 +160,8 @@ class MediaAdapter(activity: BaseSimpleActivity, var media: MutableList<Medium>,
         }
     }
 
+    fun isASectionTitle(position: Int) = thumbnailItems.getOrNull(position) is ThumbnailSection
+
     private fun checkHideBtnVisibility(menu: Menu) {
         var hiddenCnt = 0
         var unhiddenCnt = 0

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

@@ -4,4 +4,5 @@
     android:id="@+id/thumbnail_section"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
+    android:padding="@dimen/activity_margin"
     android:textSize="@dimen/bigger_text_size"/>