mirror of
https://github.com/Instagram/IGListKit
synced 2026-05-06 15:08:50 +00:00
78cca5bc43
Summary:
The collection view layout here should not be accessing the data source directly but instead asking the collection view for the number of sections and number of items. This is because the collection view holds an internal cache and if there is a discrepancy between when the collection view cache and the data source, preparing the layout will crash the app because we will send a layout down to the collection view with a items that might not exist in the collection view's cache but exist in the data source.
This diff adds an experiment to see the impact of fixing this check so that when we prepare layouts we don't ask the data source directly but ask the collection view instead. The collection view will then update it's cache and check the data source so it does not crash when we prepare a layout.
```
NSInternalInconsistencyException at __45-[UICollectionViewData validateLayoutInRect:]_block_invoke:
UICollectionView received layout attributes for a cell with an index path that does not exist:
<NSIndexPath: 0xc198a8c3ea391fbb> {length = 2, path = 4 - 0}
```
Reviewed By: lorixx
Differential Revision: D15830610
fbshipit-source-id: f3dae3e87c55b86c3b686309c1144ccfff1375bf
142 lines
6.3 KiB
Objective-C
142 lines
6.3 KiB
Objective-C
/**
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#import <UIKit/UIKit.h>
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#import <IGListKit/IGListMacros.h>
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#import <IGListKit/IGListExperiments.h>
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#import "IGListCollectionViewLayoutCompatible.h"
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NS_ASSUME_NONNULL_BEGIN
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/**
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This UICollectionViewLayout subclass is for vertically or horizontally scrolling lists of data with variable widths and
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heights. It supports an infinite number of sections and items. All work is done on the main thread, and while extremely efficient,
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care must be taken not to stall the main thread in sizing delegate methods.
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This layout piggybacks on the mechanics of UICollectionViewFlowLayout in that:
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- Your UICollectionView data source must also conform to UICollectionViewDelegateFlowLayout
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- Header support given via UICollectionElementKindSectionHeader
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All UICollectionViewDelegateFlowLayout methods are required and used by this layout:
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```
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- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;
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- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;
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- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section;
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- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section;
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- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section;
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```
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In a vertically scrolling layout, sections and items are put into the same horizontal row until the max-x position
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of an item extends beyond the width of the collection view. When that happens, the item is "newlined" to the next row.
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The y position of that row is determined by the maximum height (including section insets) of the section/item of the previous row.
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Ex. of a section (2,0) with a large width causing a newline.
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```
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|[ 0,0 ][ 1,0 ] |
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|[ 2,0 ]|
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```
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A section with a non-zero height header will always cause that section to newline. Headers are always stretched to the
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width of the collection view, pinched with the section insets.
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Ex. of a section (2,0) with a header inset on the left/right.
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```
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|[ 0,0 ][ 1,0 ] |
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| >======header=======< |
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| [ 2,0 ] |
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```
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Section insets apply to items in the section no matter if they begin on a new row or are on the same row as a previous
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section.
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Ex. of a section (2) with multiple items and a left inset.
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```
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|[ 0,0 ][ 1,0 ] >[ 2,0 ]|
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| >[ 2,1 ][ 2,2 ][ 2,3 ]|
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```
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Interitem spacing applies to items and sections within the same row. Line spacing only applies to items within the same
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section.
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In a horizontally scrolling layout, sections and items are flowed vertically until they need to be "newlined" to the
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next column. Headers, if used, are stretched to the height of the collection view, minus the section insets.
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Please see the unit tests for more configuration examples and expected output.
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*/
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NS_SWIFT_NAME(ListCollectionViewLayout)
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@interface IGListCollectionViewLayout : UICollectionViewLayout <IGListCollectionViewLayoutCompatible>
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/**
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Direction in which layout will be scrollable; items will be flowed in the perpendicular direction, "newlining" when they
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run out of space along that axis or when a non-zero header is found.
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*/
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@property (nonatomic, readonly) UICollectionViewScrollDirection scrollDirection;
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/**
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Set this to adjust the offset of the sticky headers in the scrolling direction. Can be used to change the sticky
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header position as UI like the navigation bar is scrolled offscreen. In a vertically scrolling layout, changing
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this to the height of the navigation bar will give the effect of the headers sticking to the nav as it is collapsed.
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@note Changing the value on this method will invalidate the layout every time.
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*/
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@property (nonatomic, assign) CGFloat stickyHeaderYOffset;
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/**
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Set this to `YES` to show sticky header when a section had no item. Default is `NO`.
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*/
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@property (nonatomic, assign) BOOL showHeaderWhenEmpty;
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/**
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A bitmask of experiments to conduct on the adapter.
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*/
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@property (nonatomic, assign) IGListExperiment experiments;
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/**
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Create and return a new collection view layout.
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@param stickyHeaders Set to `YES` to stick section headers to the top of the bounds while scrolling.
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@param scrollDirection Direction along which the collection view will be scrollable (if content size exceeds the frame size)
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@param topContentInset The content inset (top or left, depending on scrolling direction) used to offset the sticky headers. Ignored if stickyHeaders is `NO`.
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@param stretchToEdge Specifies whether to stretch width (in vertically scrolling layout) or height (horizontally scrolling) of last item to right/bottom edge when distance from last item to right/bottom edge < epsilon(1)
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@return A new collection view layout.
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*/
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- (instancetype)initWithStickyHeaders:(BOOL)stickyHeaders
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scrollDirection:(UICollectionViewScrollDirection)scrollDirection
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topContentInset:(CGFloat)topContentInset
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stretchToEdge:(BOOL)stretchToEdge NS_DESIGNATED_INITIALIZER;
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/**
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Create and return a new vertically scrolling collection view layout.
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@param stickyHeaders Set to `YES` to stick section headers to the top of the bounds while scrolling.
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@param topContentInset The top content inset used to offset the sticky headers. Ignored if stickyHeaders is `NO`.
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@param stretchToEdge Specifies whether to stretch width of last item to right edge when distance from last item to right edge < epsilon(1)
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@return A new collection view layout.
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*/
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- (instancetype)initWithStickyHeaders:(BOOL)stickyHeaders
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topContentInset:(CGFloat)topContentInset
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stretchToEdge:(BOOL)stretchToEdge;
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/**
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:nodoc:
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*/
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- (instancetype)init NS_UNAVAILABLE;
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/**
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:nodoc:
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*/
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+ (instancetype)new NS_UNAVAILABLE;
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@end
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NS_ASSUME_NONNULL_END
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