From 985bf48ce0794fc98ea1a4ea168e987135f05290 Mon Sep 17 00:00:00 2001
From: Ryan Nystrom <rnystrom@instagram.com>
Date: Thu, 26 Jul 2018 09:11:12 -0700
Subject: [PATCH] Default to using display handler for improved scroll perf

Summary: After experimenting with scroll performance gains, default `IGListAdapter` behavior to use the faster means of collecting visible section controllers.

Reviewed By: maxoll

Differential Revision: D8543686

fbshipit-source-id: e33a78c0f1d4f208705ff5d490ab032eb6c36e70
---
 Source/Common/IGListExperiments.h |  2 --
 Source/IGListAdapter.m            | 22 -------------------
 Tests/IGListAdapterTests.m        | 35 -------------------------------
 3 files changed, 59 deletions(-)

diff --git a/Source/Common/IGListExperiments.h b/Source/Common/IGListExperiments.h
index f38155cd..cb42c666 100644
--- a/Source/Common/IGListExperiments.h
+++ b/Source/Common/IGListExperiments.h
@@ -20,8 +20,6 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
     IGListExperimentBackgroundDiffing = 1 << 2,
     /// Test fallback to reloadData when "too many" update operations.
     IGListExperimentReloadDataFallback = 1 << 3,
-    /// Test a faster way to return visible section controllers.
-    IGListExperimentFasterVisibleSectionController = 1 << 4,
     /// Test deduping item-level updates.
     IGListExperimentDedupeItemUpdates = 1 << 5,
     /// Test deferring object creation until just before diffing.
diff --git a/Source/IGListAdapter.m b/Source/IGListAdapter.m
index 936f9b81..f45ad5b8 100644
--- a/Source/IGListAdapter.m
+++ b/Source/IGListAdapter.m
@@ -507,28 +507,6 @@
 
 - (NSArray<IGListSectionController *> *)visibleSectionControllers {
     IGAssertMainThread();
-    if (IGListExperimentEnabled(self.experiments, IGListExperimentFasterVisibleSectionController)) {
-        return [self _visibleSectionControllersFromDisplayHandler];
-    } else {
-        return [self _visibleSectionControllersFromLayoutAttributes];
-    }
-}
-
-- (NSArray<IGListSectionController *> *)_visibleSectionControllersFromLayoutAttributes {
-    NSMutableSet *visibleSectionControllers = [NSMutableSet new];
-    NSArray<UICollectionViewLayoutAttributes *> *attributes =
-    [self.collectionView.collectionViewLayout layoutAttributesForElementsInRect:self.collectionView.bounds];
-    for (UICollectionViewLayoutAttributes* attribute in attributes) {
-        IGListSectionController *sectionController = [self sectionControllerForSection:attribute.indexPath.section];
-        IGAssert(sectionController != nil, @"Section controller nil for cell in section %ld", (long)attribute.indexPath.section);
-        if (sectionController) {
-            [visibleSectionControllers addObject:sectionController];
-        }
-    }
-    return [visibleSectionControllers allObjects];
-}
-
-- (NSArray<IGListSectionController *> *)_visibleSectionControllersFromDisplayHandler {
     return [[self.displayHandler visibleListSections] allObjects];
 }
 
diff --git a/Tests/IGListAdapterTests.m b/Tests/IGListAdapterTests.m
index 9a75caad..f3bd7536 100644
--- a/Tests/IGListAdapterTests.m
+++ b/Tests/IGListAdapterTests.m
@@ -271,22 +271,6 @@
     XCTAssertTrue([visibleSectionControllers containsObject:[self.adapter sectionControllerForObject:@4]]);
 }
 
-- (void)test_whenCellsExtendBeyondBounds_withFasterExperiment_thatVisibleSectionControllersAreLimited {
-    // add experiment
-    self.adapter.experiments |= IGListExperimentFasterVisibleSectionController;
-    // # of items for each object == [item integerValue], so @2 has 2 items (cells)
-    self.dataSource.objects = @[@1, @2, @3, @4, @5, @6, @7, @8, @9, @10, @11, @12];
-    [self.adapter reloadDataWithCompletion:nil];
-    XCTAssertEqual([self.collectionView numberOfSections], 12);
-    NSArray *visibleSectionControllers = [self.adapter visibleSectionControllers];
-    // UIWindow is 100x100, each cell is 100x10 so should have the following section/cell count: 1 + 2 + 3 + 4 = 10 (100 tall)
-    XCTAssertEqual(visibleSectionControllers.count, 4);
-    XCTAssertTrue([visibleSectionControllers containsObject:[self.adapter sectionControllerForObject:@1]]);
-    XCTAssertTrue([visibleSectionControllers containsObject:[self.adapter sectionControllerForObject:@2]]);
-    XCTAssertTrue([visibleSectionControllers containsObject:[self.adapter sectionControllerForObject:@3]]);
-    XCTAssertTrue([visibleSectionControllers containsObject:[self.adapter sectionControllerForObject:@4]]);
-}
-
 - (void) test_withEmptySectionPlusFooter_thatVisibleSectionControllersAreCorrect {
     self.dataSource.objects = @[@0];
     [self.adapter reloadDataWithCompletion:nil];
@@ -304,25 +288,6 @@
     XCTAssertTrue(visibleSectionControllers.firstObject.supplementaryViewSource == supplementarySource);
 }
 
-- (void) test_withEmptySectionPlusFooter_withFasterExperiment_thatVisibleSectionControllersAreCorrect {
-    // add experiment
-    self.adapter.experiments |= IGListExperimentFasterVisibleSectionController;
-    self.dataSource.objects = @[@0];
-    [self.adapter reloadDataWithCompletion:nil];
-    IGTestSupplementarySource *supplementarySource = [IGTestSupplementarySource new];
-    supplementarySource.dequeueFromNib = YES;
-    supplementarySource.collectionContext = self.adapter;
-    supplementarySource.supportedElementKinds = @[UICollectionElementKindSectionFooter];
-    IGListSectionController *controller = [self.adapter sectionControllerForObject:@0];
-    controller.supplementaryViewSource = supplementarySource;
-    supplementarySource.sectionController = controller;
-    [self.adapter performUpdatesAnimated:NO completion:nil];
-    NSArray<IGListSectionController *> *visibleSectionControllers = [self.adapter visibleSectionControllers];
-
-    XCTAssertTrue([visibleSectionControllers count] == 1);
-    XCTAssertTrue(visibleSectionControllers.firstObject.supplementaryViewSource == supplementarySource);
-}
-
 - (void)test_whenCellsExtendBeyondBounds_thatVisibleCellsExistForSectionControllers {
     self.dataSource.objects = @[@2, @3, @4, @5, @6];
     [self.adapter reloadDataWithCompletion:nil];