Merge pull request #623 from badoo/fix-scrolled-messages-after-frame-…

…change

Use bounds height change in adjustCollectionViewInsets

Chatto/Source/ChatController/BaseChatViewController.swift

@@ -294,6 +294,7 @@ open class BaseChatViewController: UIViewController, UICollectionViewDataSource,
         return availableHeight >= contentSize.height
     }
 
+    private var previousBoundsUsedForInsetsAdjustment: CGRect? = nil
     func adjustCollectionViewInsets(shouldUpdateContentOffset: Bool) {
         guard let collectionView = self.collectionView else { return }
         let isInteracting = collectionView.panGestureRecognizer.numberOfTouches > 0
@@ -317,10 +318,22 @@ open class BaseChatViewController: UIViewController, UICollectionViewDataSource,
 
         let prevContentOffsetY = collectionView.contentOffset.y
 
+        let boundsHeightDiff: CGFloat = {
+            guard shouldUpdateContentOffset, let lastUsedBounds = self.previousBoundsUsedForInsetsAdjustment else {
+                return 0
+            }
+            let diff = lastUsedBounds.height - collectionView.bounds.height
+            // When collectionView is scrolled to bottom and height increases,
+            // collectionView adjusts its contentOffset automatically
+            let isScrolledToBottom = contentSize.height <= collectionView.bounds.maxY - collectionView.contentInset.bottom
+            return isScrolledToBottom ? max(0, diff) : diff
+        }()
+        self.previousBoundsUsedForInsetsAdjustment = collectionView.bounds
+
         let newContentOffsetY: CGFloat = {
             let minOffset = -newInsetTop
             let maxOffset = contentSize.height - (collectionView.bounds.height - newInsetBottom)
-            let targetOffset = prevContentOffsetY + insetBottomDiff
+            let targetOffset = prevContentOffsetY + insetBottomDiff + boundsHeightDiff
             return max(min(maxOffset, targetOffset), minOffset)
         }()