Full width item crashes grid layout

Summary:
Fixed #352
Closes https://github.com/Instagram/IGListKit/pull/361

Differential Revision: D4365711

Pulled By: jessesquires

fbshipit-source-id: 344b0c781cc807e0ff0bf381a5b12eaef3388d72

CHANGELOG.md

@@ -23,6 +23,8 @@ This release closes the [2.1.0 milestone](https://github.com/Instagram/IGListKit
 
 - Fix out-of-bounds bug when child section controllers in a stack remove cells. [Ryan Nystrom](https://github.com/rnystrom) [(#358)](https://github.com/Instagram/IGListKit/pull/358)
 
+- Fix a grid layout bug when item has full-width and iter-item spacing is not zero. [Bofei Zhu](https://github.com/zhubofei) [(#361)](https://github.com/Instagram/IGListKit/pull/361)
+
 2.0.0
 -----
 

Source/IGListGridCollectionViewLayout.m

@@ -219,6 +219,10 @@
         NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:i];
         id<UICollectionViewDelegateFlowLayout> delegate = (id<UICollectionViewDelegateFlowLayout>) collectionView.delegate;
         const CGSize itemSize = [delegate collectionView:collectionView layout:self sizeForItemAtIndexPath:indexPath];
+        
+        IGAssertMainThread();
+        IGAssert(itemSize.width <= self.contentWidth, @"The width of a single item must not exceed the width of the collection view.");
+        
         _IGListGridLayoutLine *lastLine = [self.lineCache lastObject];
         if (![lastLine addItemToTailWithSize:itemSize]) {
             // Not enough space for the last line
@@ -260,7 +264,7 @@
         _minimumInteritemSpacing = spacing;
         _itemSizes = [NSMutableArray array];
         _headIndex = headIndex;
-        _tailSpace = frame.size.width - self.minimumInteritemSpacing;
+        _tailSpace = frame.size.width;
     }
     return self;
 }