From 386ae0786445c06e1eabf074a4181614332f155f Mon Sep 17 00:00:00 2001
From: Ryan Nystrom <rnystrom@instagram.com>
Date: Mon, 7 Nov 2016 07:18:59 -0800
Subject: [PATCH] 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               |  1 +
 Source/IGListAdapter.h     |  7 +++++++
 Source/IGListAdapter.m     | 19 +++++++++++++++++++
 Tests/IGListAdapterTests.m | 12 ++++++++++++
 4 files changed, 39 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fc8a92008..34b7b83bf 100644
--- a/CHANGELOG.md
+++ b/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
 -----
diff --git a/Source/IGListAdapter.h b/Source/IGListAdapter.h
index 5e4f76c39..331e15d22 100644
--- a/Source/IGListAdapter.h
+++ b/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.
 
diff --git a/Source/IGListAdapter.m b/Source/IGListAdapter.m
index c7841f0c0..650d596a9 100644
--- a/Source/IGListAdapter.m
+++ b/Source/IGListAdapter.m
@@ -342,6 +342,25 @@ - (NSArray *)objects {
     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
 
diff --git a/Tests/IGListAdapterTests.m b/Tests/IGListAdapterTests.m
index 1c186db36..6563b72d6 100644
--- a/Tests/IGListAdapterTests.m
+++ b/Tests/IGListAdapterTests.m
@@ -508,4 +508,16 @@ - (void)test_whenAdapterUpdatedTwice_withThreeSections_thatSectionsUpdatedFirstL
     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