From 5cc0fcd1d77d6296f57ce1c298301b9881cb4d4a Mon Sep 17 00:00:00 2001
From: David Yamnitsky <nitsky@fb.com>
Date: Wed, 1 Feb 2017 12:11:40 -0800
Subject: [PATCH] Fix calculation of vertical and horizontal center in
 scrollToObject

Summary: Fix bug where scroll position would be incorrect in call to `-[IGListAdapter scrollToObject:supplementaryKinds:scrollDirection:scrollPosition:animated:` with scrollDirection/scrollPosition of UICollectionViewScrollDirectionVertical/UICollectionViewScrollPositionCenteredVertically or UICollectionViewScrollDirectionHorizontal/UICollectionViewScrollPositionCenteredHorizontally and with a collection view with nonzero contentInset.

Reviewed By: jessesquires

Differential Revision: D4475043

fbshipit-source-id: 4714ab0ed02e52e2d7f333624cc17858058ee57f
---
 CHANGELOG.md           |  2 ++
 Source/IGListAdapter.m | 12 ++++++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 70f4e1b5..0a3bbf69 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,8 @@ This release closes the [2.2.0 milestone](https://github.com/Instagram/IGListKit
 
 - Fix potential bug with suppressing animations (by passing `NO`) during `-[IGListAdapter performUpdatesAnimated: completion:]` where user would see UI glitches/flashing. [Jesse Squires](https://github.com/jessesquires) [(tbd)]()
 
+- Fix bug where scroll position would be incorrect in call to `-[IGListAdapter scrollToObject:supplementaryKinds:scrollDirection:scrollPosition:animated:` with scrollDirection/scrollPosition of UICollectionViewScrollDirectionVertical/UICollectionViewScrollPositionCenteredVertically or UICollectionViewScrollDirectionHorizontal/UICollectionViewScrollPositionCenteredHorizontally and with a collection view with nonzero contentInset. [David Yamnitsky](https://github.com/nitsky)
+
 2.1.0
 -----
 
diff --git a/Source/IGListAdapter.m b/Source/IGListAdapter.m
index 0e121e68..0afdb5e1 100644
--- a/Source/IGListAdapter.m
+++ b/Source/IGListAdapter.m
@@ -206,9 +206,11 @@
                 case UICollectionViewScrollPositionRight:
                     contentOffset.x = offsetMax - collectionViewWidth - contentInset.left;
                     break;
-                case UICollectionViewScrollPositionCenteredHorizontally:
-                    contentOffset.x = offsetMid - collectionViewWidth / 2.0 - contentInset.left;
+                case UICollectionViewScrollPositionCenteredHorizontally: {
+                    const CGFloat insets = (contentInset.left - contentInset.right) / 2.0;
+                    contentOffset.x = offsetMid - collectionViewWidth / 2.0 - insets;
                     break;
+                }
                 case UICollectionViewScrollPositionLeft:
                 case UICollectionViewScrollPositionNone:
                 case UICollectionViewScrollPositionTop:
@@ -223,9 +225,11 @@
                 case UICollectionViewScrollPositionBottom:
                     contentOffset.y = offsetMax - collectionViewHeight - contentInset.top;
                     break;
-                case UICollectionViewScrollPositionCenteredVertically:
-                    contentOffset.y = offsetMid - collectionViewHeight / 2.0 - contentInset.top;
+                case UICollectionViewScrollPositionCenteredVertically: {
+                    const CGFloat insets = (contentInset.top - contentInset.bottom) / 2.0;
+                    contentOffset.y = offsetMid - collectionViewHeight / 2.0 - insets;
                     break;
+                }
                 case UICollectionViewScrollPositionTop:
                 case UICollectionViewScrollPositionNone:
                 case UICollectionViewScrollPositionLeft: