我有一个背景颜色为灰色的 UICollectionView，但我希望我的其中一个部分具有白色背景。我发现这并不像我希望的那么简单(即该部分具有我可以设置的属性)。

从看How to change background color of a whole section in UICollectionView?建议使用装饰 View 和这个问题UICollectionView Decoration View通过子类化 UICollectionReusableView 和 UICollectionViewFlowLayout 帮助我更改了部分颜色。

我的问题是我无法获取部分高度(动态的)来设置 UIView 高度，而且我的后续部分的开头是空白的，直到对其进行 reloadData 调用。

到目前为止，这是我的代码: WhiteBackgroundCollectionReusableView 类:

#import <UIKit/UIKit.h>

@interface WhiteBackgroundCollectionReusableView : UICollectionReusableView

@end

@implementation WhiteBackgroundCollectionReusableView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        [self setBackgroundColor:[UIColor redColor]];
    }
    return self;
}

@end

WhiteBackgroundCollectionViewFlowLayout 类:

#import <UIKit/UIKit.h>

#import "WhiteBackgroundCollectionReusableView.h"

@interface WhiteBackgroundCollectionViewFlowLayout : UICollectionViewFlowLayout

@end

@implementation WhiteBackgroundCollectionViewFlowLayout

- (id)init
{
    self = [super init];
    if (self) {
        // Initialization code

        [self registerClass:[WhiteBackgroundCollectionReusableView class] forDecorationViewOfKind:@"WhiteSection"];
    }
    return self;
}

- (UICollectionViewLayoutAttributes*)layoutAttributesForDecorationViewOfKind:(NSString*)decorationViewKind atIndexPath:(NSIndexPath*)indexPath
{
    UICollectionViewLayoutAttributes *layoutAttributes = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:decorationViewKind withIndexPath:indexPath];

    if(indexPath.section == 0) {
        layoutAttributes.frame = CGRectMake(0.0, 0.0, self.collectionViewContentSize.width, 100);

        layoutAttributes.zIndex = -1;
    }

    return layoutAttributes;
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSMutableArray *allAttributes = [[NSMutableArray alloc] initWithCapacity:4];

    [allAttributes addObject:[self layoutAttributesForDecorationViewOfKind:@"WhiteSection" atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]]];

    for(NSInteger i = 0; i < [self.collectionView numberOfItemsInSection:0]; i++)
    {
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
        UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForItemAtIndexPath:indexPath];
        [allAttributes addObject:layoutAttributes];
    }

    return allAttributes;
}

@end

然后我将流布局分配给 viewDidLoad 中的 UICollectionViewController 中的 UICollectionView:

[_collectionView setCollectionViewLayout:[[WhiteBackgroundCollectionViewFlowLayout alloc] init]];

知道我可以从这里去哪里吗？

更新: 我已经解决了下一部分没有显示的问题。为此，我需要将 zIndex 更改为 1，因此我的 layoutAttributesForElementsInRect 函数现在如下所示:

- (NSArray*)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *array = [super layoutAttributesForElementsInRect:rect];

    for(UICollectionViewLayoutAttributes *attributes in array) {
        attributes.zIndex = 1;
    }

    NSMutableArray *newArray = [array mutableCopy];

    [newArray addObject:[self layoutAttributesForDecorationViewOfKind:@"WhiteSection" atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]]];

    for(NSInteger i = 0; i < [self.collectionView numberOfItemsInSection:0]; i++) {
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
        UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForItemAtIndexPath:indexPath];
        [newArray addObject:layoutAttributes];
    }

    array = [NSArray arrayWithArray:newArray];

    return array;
}

所以现在我只需要一种获取部分高度的方法!请帮忙! :)

最佳答案

我的解决方案可在 https://github.com/s-atif-jamil/CollectionSectionView 上找到

在SectionBackgroundLayout.h中

@interface SectionBackgroundLayout : UICollectionViewFlowLayout

@property (assign, nonatomic) BOOL alternateBackgrounds;
@property (strong, nonatomic) NSArray *decorationViewOfKinds;

@end

在SectionBackgroundLayout.m

#import "SectionBackgroundLayout.h"

@interface SectionBackgroundLayout ()

@property (strong, nonatomic) NSMutableArray *itemAttributes;

@end

@implementation SectionBackgroundLayout


- (void)prepareLayout
{
    [super prepareLayout];
    self.itemAttributes = [NSMutableArray new];

    NSInteger numberOfSection = self.collectionView.numberOfSections;
    for (int section=0; section<numberOfSection; section++)
    {
        if (!self.alternateBackgrounds && section == self.decorationViewOfKinds.count)
            break;

        NSString *decorationViewOfKind = self.decorationViewOfKinds[section % self.decorationViewOfKinds.count];
        if ([decorationViewOfKind isKindOfClass:[NSNull class]])
            continue;

        NSInteger lastIndex = [self.collectionView numberOfItemsInSection:section] - 1;
        if (lastIndex < 0)
            continue;

        UICollectionViewLayoutAttributes *firstItem = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:section]];
        UICollectionViewLayoutAttributes *lastItem = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForRow:lastIndex inSection:section]];

        CGRect frame = CGRectUnion(firstItem.frame, lastItem.frame);
        frame.origin.x -= self.sectionInset.left;
        frame.origin.y -= self.sectionInset.top;

        if (self.scrollDirection == UICollectionViewScrollDirectionHorizontal)
        {
            frame.size.width += self.sectionInset.left + self.sectionInset.right;
            frame.size.height = self.collectionView.frame.size.height;
        }
        else
        {
            frame.size.width = self.collectionView.frame.size.width;
            frame.size.height += self.sectionInset.top + self.sectionInset.bottom;
        }


        UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:decorationViewOfKind withIndexPath:[NSIndexPath indexPathForRow:0 inSection:section]];
        attributes.zIndex = -1;
        attributes.frame = frame;
        [self.itemAttributes addObject:attributes];
        [self registerNib:[UINib nibWithNibName:decorationViewOfKind bundle:[NSBundle mainBundle]] forDecorationViewOfKind:decorationViewOfKind];
    }
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSMutableArray *attributes = [NSMutableArray arrayWithArray:[super layoutAttributesForElementsInRect:rect]];
    for (UICollectionViewLayoutAttributes *attribute in self.itemAttributes)
    {
        if (!CGRectIntersectsRect(rect, attribute.frame))
            continue;

        [attributes addObject:attribute];
    }

    return attributes;
}

@end

在 View Controller 中

- (void)viewDidLoad
{
    [super viewDidLoad];
    SectionBackgroundLayout *layout = (id)self.collectionView.collectionViewLayout;
    layout.decorationViewOfKinds = @[@"SectionBackgroundView1", @"SectionBackgroundView2", [NSNull null]];
    ...
}

关于iOS:UICollectionView 上的单独部分背景颜色，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22955413/