如何在iOS7上的UICollectionView中制作粘性标题？ [英] How to make sticky headers in UICollectionView on iOS7?

问题描述

我正在使用这个解决方案来制作集合视图中的粘性标题，它在iOS6上运行良好。但是在iOS7中，如果选中在顶部栏下延伸边缘选项，则标题会粘到视图的原点，然后在导航栏后面。

I'm using this solution to make sticky headers in collection view and it works well on iOS6. But in iOS7 if the "Extend edges under top bars" option is checked then the header sticks to the origin of the view which is then behind the navigation bar.

所以现在我禁用了这个选项，但我真的想调整一下这个解决方案，让它在边缘扩展时起作用（为了获得漂亮的模糊效果）当内容滚动到导航栏后面时。）

So for now I disabled that option but I'd really like to tweak that solution to make it work when the edges are extended (in order to have the nice blurry effect when the content scrolls behind the navigation bar).

有人可以帮助我吗？或者有人有任何其他建议来实现相同的目标吗？

Can someone help me with that? Or does someone have any other suggestions to accomplish the same goal?

推荐答案

这是我的完整解决方案。只需将以下内容添加到您的FlowLayout类中：

Here is my full solution. Just add the following to your FlowLayout class:

#pragma mark STICKY HEADERS CODE BELOW
- (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 || layoutAttributes.representedElementCategory == UICollectionElementCategorySupplementaryView) {
            [missingSections addIndex:(NSUInteger) 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];
        if (layoutAttributes) {
            [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;

        CGFloat topOffset = 0;
        if ([self.collectionView.dataSource isKindOfClass:[UIViewController class]]) {
            UIViewController *collectionViewParentViewController = (UIViewController *)self.collectionView.dataSource;
            topOffset = collectionViewParentViewController.topLayoutGuide.length;
        }

        CGPoint const contentOffset = CGPointMake(cv.contentOffset.x, cv.contentOffset.y + topOffset);
        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 {
            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;
}

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