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A simple sample that shows how to make suplementary views stick.
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Derrick J. Hathaway
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Jun 4, 2013
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StickyViews.xcodeproj/project.xcworkspace/contents.xcworkspacedata
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| Original file line number | Diff line number | Diff line change |
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| // | ||
| // MyHeaderOrFooterView.h | ||
| // StickyViews | ||
| // | ||
| // Created by derrick on 6/4/13. | ||
| // Copyright (c) 2013 derrh. All rights reserved. | ||
| // | ||
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| #import <UIKit/UIKit.h> | ||
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| @interface MyHeaderOrFooterView : UICollectionReusableView | ||
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| @end |
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| Original file line number | Diff line number | Diff line change |
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| // | ||
| // MyHeaderOrFooterView.m | ||
| // StickyViews | ||
| // | ||
| // Created by derrick on 6/4/13. | ||
| // Copyright (c) 2013 derrh. All rights reserved. | ||
| // | ||
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| #import "MyHeaderOrFooterView.h" | ||
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| @implementation MyHeaderOrFooterView | ||
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| - (id)initWithFrame:(CGRect)frame | ||
| { | ||
| self = [super initWithFrame:frame]; | ||
| if (self) { | ||
| // Initialization code | ||
| } | ||
| return self; | ||
| } | ||
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| /* | ||
| // Only override drawRect: if you perform custom drawing. | ||
| // An empty implementation adversely affects performance during animation. | ||
| - (void)drawRect:(CGRect)rect | ||
| { | ||
| // Drawing code | ||
| } | ||
| */ | ||
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| @end |
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| Original file line number | Diff line number | Diff line change |
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| // | ||
| // MyLayout.h | ||
| // StickyViews | ||
| // | ||
| // Created by derrick on 6/4/13. | ||
| // Copyright (c) 2013 derrh. All rights reserved. | ||
| // | ||
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| #import <UIKit/UIKit.h> | ||
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| @interface MyLayout : UICollectionViewFlowLayout | ||
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| @end |
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| Original file line number | Diff line number | Diff line change |
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| // | ||
| // MyLayout.m | ||
| // StickyViews | ||
| // | ||
| // Created by derrick on 6/4/13. | ||
| // Copyright (c) 2013 derrh. All rights reserved. | ||
| // | ||
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| #import "MyLayout.h" | ||
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| @implementation MyLayout | ||
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| /* in order to make the header and footer float (or stick to the | ||
| top and bottom of the screen), we need to invalidate the layout | ||
| on bounds change (when scrolling). | ||
| */ | ||
| - (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds | ||
| { | ||
| return YES; | ||
| } | ||
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| /* override this method so that you can add your header and footer | ||
| to the list of UICollectionReusableView's that will be requested | ||
| from your dataSource. | ||
| */ | ||
| - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect | ||
| { | ||
| NSMutableArray *allItems = [[super layoutAttributesForElementsInRect:rect] mutableCopy]; | ||
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| __block BOOL headerFound = NO; | ||
| __block BOOL footerFound = NO; | ||
| [allItems enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { | ||
| if ([[obj representedElementKind] isEqualToString:UICollectionElementKindSectionHeader]) { | ||
| headerFound = YES; | ||
| [self updateHeaderAttributes:obj]; | ||
| } else if ([[obj representedElementKind] isEqualToString:UICollectionElementKindSectionFooter]) { | ||
| footerFound = YES; | ||
| [self updateFooterAttributes:obj]; | ||
| } | ||
| }]; | ||
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| // Flow layout will remove items from the list if they are supposed to be off screen, so we add them | ||
| // back in in those cases. | ||
| if (!headerFound) { | ||
| [allItems addObject:[self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:[NSIndexPath indexPathForItem:[allItems count] inSection:0]]]; | ||
| } | ||
| if (!footerFound) { | ||
| [allItems addObject:[self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionFooter atIndexPath:[NSIndexPath indexPathForItem:[allItems count] inSection:0]]]; | ||
| } | ||
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| return allItems; | ||
| } | ||
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| /* now provide the layout attributes for your floating header/footer. */ | ||
| - (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath | ||
| { | ||
| UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForSupplementaryViewOfKind:kind withIndexPath:indexPath]; | ||
| attributes.size = CGSizeMake(self.collectionView.bounds.size.width, 44); | ||
| if ([kind isEqualToString:UICollectionElementKindSectionHeader]) { | ||
| [self updateHeaderAttributes:attributes]; | ||
| } else { | ||
| [self updateFooterAttributes:attributes]; | ||
| } | ||
| return attributes; | ||
| } | ||
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| #pragma mark - make things stick | ||
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| - (void)updateHeaderAttributes:(UICollectionViewLayoutAttributes *)attributes | ||
| { | ||
| CGRect currentBounds = self.collectionView.bounds; | ||
| attributes.zIndex = 1; | ||
| attributes.hidden = NO; | ||
| CGFloat yCenterOffset = currentBounds.origin.y + attributes.size.height/2.f; | ||
| attributes.center = CGPointMake(CGRectGetMidX(currentBounds), yCenterOffset); | ||
| } | ||
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| - (void)updateFooterAttributes:(UICollectionViewLayoutAttributes *)attributes | ||
| { | ||
| CGRect currentBounds = self.collectionView.bounds; | ||
| attributes.zIndex = 1; | ||
| attributes.hidden = NO; | ||
| CGFloat yCenterOffset = currentBounds.origin.y + currentBounds.size.height - attributes.size.height/2.0f; | ||
| attributes.center = CGPointMake(CGRectGetMidX(currentBounds), yCenterOffset); | ||
| } | ||
| @end |
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