Add visibleObjects API

Summary: Adding this API to make querying visible objects a little easier. Fixes #164.

Reviewed By: dshahidehpour

Differential Revision: D4138472

fbshipit-source-id: 0136c39e17c72941b85284b7f3b5494b1ddabf68

CHANGELOG.md

@@ -21,6 +21,7 @@ This release closes the [2.0.0 milestone](https://github.com/Instagram/IGListKit
 - Added support for cells created from storyboard. [Bofei Zhu](https://github.com/zhubofei) [(#92)](https://github.com/Instagram/IGListKit/pull/92)
 - Added examples for Today & iMessage extensions. [Sherlouk](https://github.com/Sherlouk) [(#112)](https://github.com/Instagram/IGListKit/pull/112)
 - Added `tvOS` support. [Jesse Squires](https://github.com/jessesquires) [(#137)](https://github.com/Instagram/IGListKit/pull/137)
+- Added new `-[IGListAdapter visibleObjects]` API. [Ryan Nystrom](https://github.com/rnystrom)
 
 1.0.0
 -----

Source/IGListAdapter.h

@@ -168,6 +168,13 @@ IGLK_SUBCLASSING_RESTRICTED
  */
 - (NSArray<IGListSectionController<IGListSectionType> *> *)visibleSectionControllers;
 
+/**
+ An unordered array of the currently visible objects.
+
+ @return An array of objects
+ */
+- (NSArray *)visibleObjects;
+
 /**
  Scroll to an object in the list adapter.
 

Source/IGListAdapter.m

@@ -342,6 +342,25 @@
     return [visibleSectionControllers allObjects];
 }
 
+- (NSArray *)visibleObjects {
+    IGAssertMainThread();
+    NSArray<UICollectionViewCell *> *visibleCells = [self.collectionView visibleCells];
+    NSMutableSet *visibleObjects = [NSMutableSet new];
+    for (UICollectionViewCell *cell in visibleCells) {
+        IGListSectionController<IGListSectionType> *sectionController = [self sectionControllerForCell:cell];
+        IGAssert(sectionController != nil, @"Section controller nil for cell %@", cell);
+        if (sectionController != nil) {
+            const NSUInteger section = [self sectionForSectionController:sectionController];
+            id object = [self objectAtSection:section];
+            IGAssert(object != nil, @"Object not found for section controller %@ at section %zi", sectionController, section);
+            if (object != nil) {
+                [visibleObjects addObject:object];
+            }
+        }
+    }
+    return [visibleObjects allObjects];
+}
+
 
 #pragma mark - Layout
 

Tests/IGListAdapterTests.m

@@ -508,4 +508,16 @@
     XCTAssertFalse([[self.adapter sectionControllerForObject:@2] isLastSection]);
 }
 
+- (void)test_whenAdapterUpdated_withObjectsOverflow_thatVisibleObjectsIsSubsetOfAllObjects {
+    // each section controller returns n items sized 100x10
+    self.dataSource.objects = @[@1, @2, @3, @4, @5, @6];
+    [self.adapter reloadDataWithCompletion:nil];
+    self.collectionView.contentOffset = CGPointMake(0, 30);
+    [self.collectionView layoutIfNeeded];
+
+    NSArray *visibleObjects = [[self.adapter visibleObjects] sortedArrayUsingSelector:@selector(compare:)];
+    NSArray *expectedObjects = @[@3, @4, @5];
+    XCTAssertEqualObjects(visibleObjects, expectedObjects);
+}
+
 @end