UICollectionView的header悬停

UICollectionView的header悬停，继承UICollectionViewFlowLayout，重写相关方法

 

 

//

//  StickyHeaderLayout.h

//  Wombat

//

//  Created by Todd Laney on 1/9/13.

//  Copyright (c) 2013 ToddLa. All rights reserved.

//

//  Modified from http://blog.radi.ws/post/32905838158/sticky-headers-for-uicollectionview-using THANKS!

//

 

#import <UIKit/UIKit.h>

 

@interface StickyHeaderLayout : UICollectionViewFlowLayout

 

@end

 

//

//  StickyHeaderFlowLayout.m

//  Wombat

//

//  Created by Todd Laney on 1/9/13.

//  Copyright (c) 2013 ToddLa. All rights reserved.

//

//  Modified from http://blog.radi.ws/post/32905838158/sticky-headers-for-uicollectionview-using THANKS!

//

 

#import "StickyHeaderFlowLayout.h"

 

@implementation StickyHeaderFlowLayout

 

- (NSArray *) layoutAttributesForElementsInRect:(CGRect)rect {

 

    NSMutableArray *answer = [[super layoutAttributesForElementsInRect:rect] mutableCopy];

    

    NSMutableIndexSet *missingSections = [NSMutableIndexSet indexSet];

    for (NSUInteger idx=0; idx<[answer count]; idx++) {

        UICollectionViewLayoutAttributes *layoutAttributes = answer[idx];

        

        if (layoutAttributes.representedElementCategory == UICollectionElementCategoryCell) {

            [missingSections addIndex:layoutAttributes.indexPath.section];  // remember that we need to layout header for this section

        }

        if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {

            [answer removeObjectAtIndex:idx];  // remove layout of header done by our super, we will do it right later

            idx--;

        }

    }

    

    // layout all headers needed for the rect using self code

    [missingSections enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {

        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:idx];

        UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];

        [answer addObject:layoutAttributes];

    }];

    

    return answer;

}

 

- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {

    UICollectionViewLayoutAttributes *attributes = [super layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:indexPath];

    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {

        UICollectionView * const cv = self.collectionView;

        CGPoint const contentOffset = cv.contentOffset;

        CGPoint nextHeaderOrigin = CGPointMake(INFINITY, INFINITY);

        

        if (indexPath.section+1 < [cv numberOfSections]) {

            UICollectionViewLayoutAttributes *nextHeaderAttributes = [super layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:[NSIndexPath indexPathForItem:0 inSection:indexPath.section+1]];

            nextHeaderOrigin = nextHeaderAttributes.frame.origin;

        }

        

        CGRect frame = attributes.frame;

        if (self.scrollDirection == UICollectionViewScrollDirectionVertical) {

            frame.origin.y = MIN(MAX(contentOffset.y, frame.origin.y), nextHeaderOrigin.y - CGRectGetHeight(frame));

        }

        else { // UICollectionViewScrollDirectionHorizontal

            frame.origin.x = MIN(MAX(contentOffset.x, frame.origin.x), nextHeaderOrigin.x - CGRectGetWidth(frame));

        }

        attributes.zIndex = 1024;

        attributes.frame = frame;

    }

    return attributes;

}

 

- (UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {

    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:indexPath];

    return attributes;

}

- (UICollectionViewLayoutAttributes *)finalLayoutAttributesForDisappearingSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {

    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:indexPath];

    return attributes;

}

 

- (BOOL) shouldInvalidateLayoutForBoundsChange:(CGRect)newBound {

    return YES;

}

 

@end

 

来源：https://gist.github.com/evadne/4544569