Allow UICollectionViewLayout to Provide Layout Inspector, Always Update Delegate (#3003)

* Allow UICollectionViewLayout to give us a layout inspector, always call the didChangeDelegate/didChangeDataSource on binding

* Make an assertion

* Update the tests

* Tests use actual layout inspector

* Be more consistent

Author: Adlai Holler

AsyncDisplayKit/ASCollectionView.mm

@@ -533,19 +533,14 @@ - (void)setCollectionViewLayout:(UICollectionViewLayout *)collectionViewLayout
 - (id<ASCollectionViewLayoutInspecting>)layoutInspector
 {
   if (_layoutInspector == nil) {
-    UICollectionViewFlowLayout *layout = (UICollectionViewFlowLayout *)self.collectionViewLayout;
+    UICollectionViewLayout *layout = self.collectionViewLayout;
     if (layout == nil) {
       // Layout hasn't been set yet, we're still init'ing
       return nil;
     }
-    
-    if ([layout asdk_isFlowLayout]) {
-      // Register the default layout inspector delegate for flow layouts only
-      _defaultLayoutInspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:self flowLayout:layout];
-    } else {
-      // Register the default layout inspector delegate for custom collection view layouts
-      _defaultLayoutInspector = [[ASCollectionViewLayoutInspector alloc] initWithCollectionView:self];
-    }
+
+    _defaultLayoutInspector = [layout asdk_layoutInspector];
+    ASDisplayNodeAssertNotNil(_defaultLayoutInspector, @"You must not return nil from -asdk_layoutInspector. Return [super asdk_layoutInspector] if you have to! Layout: %@", layout);
 
     // Explicitly call the setter to wire up the _layoutInspectorFlags
     self.layoutInspector = _defaultLayoutInspector;
@@ -560,6 +555,13 @@ - (void)setLayoutInspector:(id<ASCollectionViewLayoutInspecting>)layoutInspector
 
   _layoutInspectorFlags.didChangeCollectionViewDataSource = [_layoutInspector respondsToSelector:@selector(didChangeCollectionViewDataSource:)];
   _layoutInspectorFlags.didChangeCollectionViewDelegate = [_layoutInspector respondsToSelector:@selector(didChangeCollectionViewDelegate:)];
+
+  if (_layoutInspectorFlags.didChangeCollectionViewDataSource) {
+    [_layoutInspector didChangeCollectionViewDataSource:self.asyncDataSource];
+  }
+  if (_layoutInspectorFlags.didChangeCollectionViewDelegate) {
+    [_layoutInspector didChangeCollectionViewDelegate:self.asyncDelegate];
+  }
 }
 
 - (void)setTuningParameters:(ASRangeTuningParameters)tuningParameters forRangeType:(ASLayoutRangeType)rangeType

AsyncDisplayKit/Details/ASCollectionViewLayoutInspector.h

@@ -72,11 +72,12 @@ extern ASSizeRange NodeConstrainedSizeForScrollDirection(ASCollectionView *colle
  * A layout inspector for non-flow layouts that returns a constrained size to let the cells layout itself as
  * far as possible based on the scrollable direction of the collection view. It throws exceptions for delegate
  * methods that are related to supplementary node's management.
+ *
+ * @warning This class is not meant to be subclassed and will be restricted in the future.
  */
 @interface ASCollectionViewLayoutInspector : NSObject <ASCollectionViewLayoutInspecting>
 
-- (instancetype)init NS_UNAVAILABLE;
-- (instancetype)initWithCollectionView:(ASCollectionView *)collectionView NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithCollectionView:(ASCollectionView *)collectionView ASDISPLAYNODE_DEPRECATED_MSG("Use -init instead.");
 
 @end
 

AsyncDisplayKit/Details/ASCollectionViewLayoutInspector.m

@@ -39,11 +39,7 @@ @implementation ASCollectionViewLayoutInspector {
 
 - (instancetype)initWithCollectionView:(ASCollectionView *)collectionView
 {
-  self = [super init];
-  if (self != nil) {
-    [self didChangeCollectionViewDelegate:collectionView.asyncDelegate];
-  }
-  return self;
+  return [self init];
 }
 
 #pragma mark ASCollectionViewLayoutInspecting

AsyncDisplayKit/Details/UICollectionViewLayout+ASConvenience.h

@@ -8,13 +8,21 @@
 //  of patent rights can be found in the PATENTS file in the same directory.
 //
 
-#import <UIKit/UIKit.h>
+#import <UIKit/UICollectionViewLayout.h>
+
+@protocol ASCollectionViewLayoutInspecting;
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface UICollectionViewLayout (ASConvenience)
+@interface UICollectionViewLayout (ASLayoutInspectorProviding)
 
-- (BOOL)asdk_isFlowLayout;
+/**
+ * You can override this method on your @c UICollectionViewLayout subclass to
+ * return a layout inspector tailored to your layout.
+ *
+ * It's fine to return @c self. You must not return @c nil.
+ */
+- (id<ASCollectionViewLayoutInspecting>)asdk_layoutInspector;
 
 @end
 

AsyncDisplayKit/Details/UICollectionViewLayout+ASConvenience.m

@@ -10,11 +10,20 @@
 
 #import <AsyncDisplayKit/UICollectionViewLayout+ASConvenience.h>
 
-@implementation UICollectionViewLayout (ASConvenience)
+#import <UIKit/UICollectionViewFlowLayout.h>
 
-- (BOOL)asdk_isFlowLayout
+#import <AsyncDisplayKit/ASCollectionViewFlowLayoutInspector.h>
+
+@implementation UICollectionViewLayout (ASLayoutInspectorProviding)
+
+- (id<ASCollectionViewLayoutInspecting>)asdk_layoutInspector
 {
-  return [self isKindOfClass:[UICollectionViewFlowLayout class]];
+  UICollectionViewFlowLayout *flow = ASDynamicCast(self, UICollectionViewFlowLayout);
+  if (flow != nil) {
+    return [[ASCollectionViewFlowLayoutInspector alloc] initWithFlowLayout:flow];
+  } else {
+    return [[ASCollectionViewLayoutInspector alloc] init];
+  }
 }
 
 @end

AsyncDisplayKit/Private/ASCollectionViewFlowLayoutInspector.h

@@ -24,7 +24,7 @@ AS_SUBCLASSING_RESTRICTED
 @property (nonatomic, weak, readonly) UICollectionViewFlowLayout *layout;
 
 - (instancetype)init NS_UNAVAILABLE;
-- (instancetype)initWithCollectionView:(ASCollectionView *)collectionView flowLayout:(UICollectionViewFlowLayout *)flowLayout NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithFlowLayout:(UICollectionViewFlowLayout *)flowLayout NS_DESIGNATED_INITIALIZER;
 
 @end
 

AsyncDisplayKit/Private/ASCollectionViewFlowLayoutInspector.m

@@ -36,14 +36,12 @@ @implementation ASCollectionViewFlowLayoutInspector {
 
 #pragma mark Lifecycle
 
-- (instancetype)initWithCollectionView:(ASCollectionView *)collectionView flowLayout:(UICollectionViewFlowLayout *)flowLayout;
+- (instancetype)initWithFlowLayout:(UICollectionViewFlowLayout *)flowLayout;
 {
-  NSParameterAssert(collectionView);
   NSParameterAssert(flowLayout);
 
   self = [super init];
   if (self != nil) {
-    [self didChangeCollectionViewDelegate:collectionView.asyncDelegate];
     _layout = flowLayout;
   }
   return self;

AsyncDisplayKitTests/ASCollectionViewFlowLayoutInspectorTests.m

@@ -143,7 +143,7 @@ - (void)testThatItReturnsAVerticalConstrainedSizeFromTheHeaderDelegateImplementa
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionHeader atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(collectionView.bounds.size.width, 125.0));
 
@@ -166,7 +166,7 @@ - (void)testThatItReturnsAVerticalConstrainedSizeFromTheFooterDelegateImplementa
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionFooter atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(collectionView.bounds.size.width, 125.0));
   ASXCTAssertEqualSizeRanges(size, sizeCompare, @"should have a size constrained by the values returned in the delegate implementation");
@@ -189,7 +189,7 @@ - (void)testThatItReturnsAVerticalConstrainedSizeFromTheHeaderProperty
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:rect collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionHeader atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(collectionView.bounds.size.width, 125.0));
   ASXCTAssertEqualSizeRanges(size, sizeCompare, @"should have a size constrained by the size set on the layout");
@@ -210,7 +210,7 @@ - (void)testThatItReturnsAVerticalConstrainedSizeFromTheFooterProperty
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:rect collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionFooter atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(collectionView.bounds.size.width, 125.0));
   ASXCTAssertEqualSizeRanges(size, sizeCompare, @"should have a size constrained by the size set on the layout");
@@ -234,7 +234,7 @@ - (void)testThatItReturnsAHorizontalConstrainedSizeFromTheHeaderDelegateImplemen
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionHeader atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(125.0, collectionView.bounds.size.height));
   ASXCTAssertEqualSizeRanges(size, sizeCompare, @"should have a size constrained by the values returned in the delegate implementation");
@@ -256,7 +256,7 @@ - (void)testThatItReturnsAHorizontalConstrainedSizeFromTheFooterDelegateImplemen
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionFooter atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(125.0, collectionView.bounds.size.height));
   ASXCTAssertEqualSizeRanges(size, sizeCompare, @"should have a size constrained by the values returned in the delegate implementation");
@@ -279,7 +279,7 @@ - (void)testThatItReturnsAHorizontalConstrainedSizeFromTheHeaderProperty
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:rect collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionHeader atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(125.0, collectionView.bounds.size.width));
   ASXCTAssertEqualSizeRanges(size, sizeCompare, @"should have a size constrained by the size set on the layout");
@@ -300,7 +300,7 @@ - (void)testThatItReturnsAHorizontalConstrainedSizeFromTheFooterProperty
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:rect collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
 
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionFooter atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeMake(125.0, collectionView.bounds.size.height));
   ASXCTAssertEqualSizeRanges(size, sizeCompare, @"should have a size constrained by the size set on the layout");
@@ -317,7 +317,7 @@ - (void)testThatItReturnsZeroSizeWhenNoReferenceSizeIsImplemented
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   ASSizeRange size = [inspector collectionView:collectionView constrainedSizeForSupplementaryNodeOfKind:UICollectionElementKindSectionFooter atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
   ASSizeRange sizeCompare = ASSizeRangeMake(CGSizeZero, CGSizeZero);
   XCTAssert(CGSizeEqualToSize(size.min, sizeCompare.min) && CGSizeEqualToSize(size.max, sizeCompare.max), @"should have a zero size");
@@ -336,7 +336,7 @@ - (void)testThatItReturnsOneWhenAValidSizeIsImplementedOnTheDelegate
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   NSUInteger count = [inspector collectionView:collectionView supplementaryNodesOfKind:UICollectionElementKindSectionHeader inSection:0];
   XCTAssert(count == 1, @"should have a header supplementary view");
 
@@ -353,7 +353,7 @@ - (void)testThatItReturnsOneWhenAValidSizeIsImplementedOnTheLayout
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   NSUInteger count = [inspector collectionView:collectionView supplementaryNodesOfKind:UICollectionElementKindSectionFooter inSection:0];
   XCTAssert(count == 1, @"should have a footer supplementary view");
 
@@ -369,7 +369,7 @@ - (void)testThatItReturnsNoneWhenNoReferenceSizeIsImplemented
   ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
   collectionView.asyncDataSource = dataSource;
   collectionView.asyncDelegate = delegate;
-  ASCollectionViewFlowLayoutInspector *inspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:collectionView flowLayout:layout];
+  ASCollectionViewFlowLayoutInspector *inspector = ASDynamicCast(collectionView.layoutInspector, ASCollectionViewFlowLayoutInspector);
   NSUInteger count = [inspector collectionView:collectionView supplementaryNodesOfKind:UICollectionElementKindSectionFooter inSection:0];
   XCTAssert(count == 0, @"should not have a footer supplementary view");
 
@@ -393,7 +393,7 @@ - (void)testThatItThrowsIfNodeConstrainedSizeIsImplementedOnDataSourceButNotOnDe
   id delegate = [InspectorTestDataSourceDelegateWithoutNodeConstrainedSize new];
   node.delegate = delegate;
 
-  ASCollectionViewLayoutInspector *inspector = [[ASCollectionViewLayoutInspector alloc] initWithCollectionView:collectionView];
+  ASCollectionViewLayoutInspector *inspector = [[ASCollectionViewLayoutInspector alloc] init];
 
   collectionView.layoutInspector = inspector;
   XCTAssertThrows([inspector collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath]);