Skip reloading objects that are not found

Summary:
Even with the assert, we will add `NSNotFound` to the set which will crash. Instead, skip adding the value in case a consumer is using a reference to an object that doesn't exist anymore.

Also, should be using `continue` if a section controller isn't returned by the data source.

Reviewed By: jessesquires

Differential Revision: D4226771

fbshipit-source-id: ed6df0992fdef611dd8fae64f4716e296df11f9a

CHANGELOG.md

@@ -82,6 +82,8 @@ This release closes the [2.0.0 milestone](https://github.com/Instagram/IGListKit
 
 - Prevent `UICollectionView` bug when accessing a cell during working range updates. [Ryan Nystrom](https://github.com/rnystrom) [(#216)](https://github.com/Instagram/IGListKit/pull/216)
 
+- Skip reloading for objects that are not found when calling `-[IGListAdapter reloadObjects:]`. [Ryan Nystrom](https://github.com/rnystrom) (tbd)
+
 ### Documentation
 
 - We now have 100% documentation coverage. Docs been refined and clarified. [Jesse Squires](https://github.com/jessesquires) [(#207)](https://github.com/Instagram/IGListKit/pull/207)

Source/IGListAdapter.m

@@ -311,8 +311,11 @@
 
     for (id object in objects) {
         // look up the item using the map's lookup function. might not be the same item
-        NSUInteger section = [map sectionForObject:object];
-        IGAssert(section != NSNotFound, @"Did not find a section for item %@", object);
+        const NSInteger section = [map sectionForObject:object];
+        const BOOL notFound = section == NSNotFound;
+        if (notFound) {
+            continue;
+        }
         [sections addIndex:section];
 
         // reverse lookup the item using the section. if the pointer has changed the trigger update events and swap items
@@ -465,7 +468,7 @@
 
         IGAssert(sectionController != nil, @"Data source <%@> cannot return a nil section controller.", self.dataSource);
         if (sectionController == nil) {
-            break;
+            continue;
         }
 
         // in case the section controller was created outside of -listAdapter:sectionControllerForObject:

Tests/IGListAdapterTests.m

@@ -843,4 +843,11 @@ XCTAssertEqual(CGPointEqualToPoint(point, p), YES); \
     [mockScrollDelegate verify];
 }
 
+- (void)test_whenReloadingObjectsThatDontExist_thatAdapterContinues {
+    self.dataSource.objects = @[@0, @1, @2];
+    [self.adapter reloadDataWithCompletion:nil];
+    [self.adapter reloadObjects:@[@1, @3]];
+    XCTAssertEqual(self.collectionView.numberOfSections, 3);
+}
+
 @end