Container size doesnt use content inset, add new APIs

Summary:
The content inset of a collection view can change at any time (as it does with our refresh control) and isn't a good measure of the container size. I don't want to totally remove that API though, so I changed the default behavior, added an insets API, and also added the functionality of the original in a new API.

This makes sizes much more deterministic.

Reviewed By: jessesquires

Differential Revision: D4800758

fbshipit-source-id: 85ce843b5b1c297cea2e2ea705fa255617cbe356

CHANGELOG.md

@@ -52,6 +52,8 @@ This release closes the [3.0.0 milestone](https://github.com/Instagram/IGListKit
 } completion:nil];
 ```
 
+- `-[IGListCollectionContext containerSize]` no longer accounts for the content inset of the collection view when returning a size. If you require that behavior, you can now use `-[IGListCollectionContext insetContainerSize]`. [Ryan Nystrom](https://github.com/rnystrom) (tbd)
+
 
 ### Enhancements
 

Examples/Examples-iOS/IGListKitExamples/SectionControllers/ImageSectionController.m

@@ -15,6 +15,10 @@
 #import "ImageSectionController.h"
 #import "PhotoCell.h"
 
+@interface ImageSectionController () <IGListSupplementaryViewSource>
+
+@end
+
 @implementation ImageSectionController
 
 #pragma mark - IGListSectionType
@@ -39,4 +43,22 @@ - (void)didSelectItemAtIndex:(NSInteger)index {
 
 }
 
+- (id<IGListSupplementaryViewSource>)supplementaryViewSource {
+    return self;
+}
+
+- (NSArray<NSString *> *)supportedElementKinds {
+    return @[UICollectionElementKindSectionFooter];
+}
+
+- (CGSize)sizeForSupplementaryViewOfKind:(NSString *)elementKind atIndex:(NSInteger)index {
+    return CGSizeMake(self.collectionContext.containerSize.width, 30);
+}
+
+- (UICollectionReusableView *)viewForSupplementaryElementOfKind:(NSString *)elementKind atIndex:(NSInteger)index {
+    UICollectionReusableView *view = [self.collectionContext dequeueReusableSupplementaryViewOfKind:elementKind forSectionController:self class:[UICollectionReusableView class] atIndex:index];
+    view.backgroundColor = [UIColor yellowColor];
+    return view;
+}
+
 @end

Source/IGListAdapter.m

@@ -817,7 +817,16 @@ - (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL
 #pragma mark - IGListCollectionContext
 
 - (CGSize)containerSize {
-    return UIEdgeInsetsInsetRect(self.collectionView.bounds, self.collectionView.contentInset).size;
+    return self.collectionView.bounds.size;
+}
+
+- (UIEdgeInsets)containerInset {
+    return self.collectionView.contentInset;
+}
+
+- (CGSize)insetContainerSize {
+    IGListCollectionView *collectionView = self.collectionView;
+    return UIEdgeInsetsInsetRect(collectionView.bounds, collectionView.contentInset).size;
 }
 
 - (CGSize)containerSizeForSectionController:(IGListSectionController<IGListSectionType> *)sectionController {

Source/IGListCollectionContext.h

@@ -24,10 +24,20 @@ NS_ASSUME_NONNULL_BEGIN
 @protocol IGListCollectionContext <NSObject>
 
 /**
- The size of the collection view. You may use this for sizing cells.
+ The size of the collection view. You can use this for sizing cells.
  */
 @property (nonatomic, readonly) CGSize containerSize;
 
+/**
+ The content insets of the collection view. You can use this for sizing cells.
+ */
+@property (nonatomic, readonly) UIEdgeInsets containerInset;
+
+/**
+ The size of the collection view with content insets applied.
+ */
+@property (nonatomic, readonly) CGSize insetContainerSize;
+
 /**
  Returns size of the collection view relative to the section controller.
  

Source/IGListStackedSectionController.m

@@ -165,6 +165,14 @@ - (CGSize)containerSize {
     return [self.collectionContext containerSize];
 }
 
+- (UIEdgeInsets)containerInset {
+    return [self.collectionContext containerInset];
+}
+
+- (CGSize)insetContainerSize {
+    return [self.collectionContext insetContainerSize];
+}
+
 - (CGSize)containerSizeForSectionController:(IGListSectionController<IGListSectionType> *)sectionController {
     const UIEdgeInsets inset = sectionController.inset;
     return CGSizeMake(self.containerSize.width - inset.left - inset.right,

Tests/IGListAdapterTests.m

@@ -1111,4 +1111,26 @@ - (void)test_whenSupplementarySourceReturnsNegativeSize_thatAdapterReturnsZero {
     XCTAssertEqual(size.height, 0.0);
 }
 
+- (void)test_whenQueryingContainerInset_thatMatchesCollectionView {
+    self.dataSource.objects = @[@2];
+    [self.adapter reloadDataWithCompletion:nil];
+    self.collectionView.contentInset = UIEdgeInsetsMake(1, 2, 3, 4);
+    IGListSectionController<IGListSectionType> *controller = [self.adapter sectionControllerForObject:@2];
+    const UIEdgeInsets inset = [controller.collectionContext containerInset];
+    XCTAssertEqual(inset.top, 1);
+    XCTAssertEqual(inset.left, 2);
+    XCTAssertEqual(inset.bottom, 3);
+    XCTAssertEqual(inset.right, 4);
+}
+
+- (void)test_whenQueryingInsetContainerSize_thatResultIsBoundsInsetByContent {
+    self.dataSource.objects = @[@2];
+    [self.adapter reloadDataWithCompletion:nil];
+    self.collectionView.contentInset = UIEdgeInsetsMake(1, 2, 3, 4);
+    IGListSectionController<IGListSectionType> *controller = [self.adapter sectionControllerForObject:@2];
+    const CGSize size = [controller.collectionContext insetContainerSize];
+    XCTAssertEqual(size.width, 94);
+    XCTAssertEqual(size.height, 96);
+}
+
 @end

Tests/IGListStackSectionControllerTests.m

@@ -158,6 +158,32 @@ - (void)test_whenSectionEdgeInsetIsNotZero {
     IGAssertEqualSize([stack containerSizeForSectionController:section1], 98, 98);
 }
 
+- (void)test_whenQueryingContainerInset_thatMatchesCollectionView {
+    self.collectionView.contentInset = UIEdgeInsetsMake(1, 2, 3, 4);
+    [self setupWithObjects:@[
+                             [[IGTestObject alloc] initWithKey:@0 value:@[@42]]
+                             ]];
+    IGListStackedSectionController *stack = [self.adapter sectionControllerForObject:self.dataSource.objects[0]];
+    IGListTestContainerSizeSection *section1 = stack.sectionControllers[0];
+    const UIEdgeInsets inset = [section1.collectionContext containerInset];
+    XCTAssertEqual(inset.top, 1);
+    XCTAssertEqual(inset.left, 2);
+    XCTAssertEqual(inset.bottom, 3);
+    XCTAssertEqual(inset.right, 4);
+}
+
+- (void)test_whenQueryingInsetContainerSize_thatBoundsInsetByContent {
+    self.collectionView.contentInset = UIEdgeInsetsMake(1, 2, 3, 4);
+    [self setupWithObjects:@[
+                             [[IGTestObject alloc] initWithKey:@0 value:@[@42]]
+                             ]];
+    IGListStackedSectionController *stack = [self.adapter sectionControllerForObject:self.dataSource.objects[0]];
+    IGListTestContainerSizeSection *section1 = stack.sectionControllers[0];
+    const CGSize size = [section1.collectionContext insetContainerSize];
+    XCTAssertEqual(size.width, 94);
+    XCTAssertEqual(size.height, 96);
+}
+
 - (void)test_whenQueryingCellIndex_thatIndexIsRelativeToSectionController {
     [self setupWithObjects:@[
                              [[IGTestObject alloc] initWithKey:@0 value:@[@1, @1, @2]]