cocoa-touch - 空 Collection View 中的 UICollectionView 装饰

Question

我已经实现了一个 UICollectionView带有自定义布局。它为布局添加了装饰 View 。我使用以下代码添加装饰 View 的布局属性:

-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *allAttributes = [super layoutAttributesForElementsInRect:rect];
    return [allAttributes arrayByAddingObject:[self layoutAttributesForDecorationViewOfKind:kHeaderKind atIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]]];
}

集合 View 中的数据由 NSFetchedResultsController 提供.

现在看起来它工作正常，但是当集合 View 为空时，它会失败，因为有第 0 部分。尝试在没有索引路径的情况下使用它，但也失败了。关于如何在空的 UICollectionView 中使用装饰 View 的任何想法?应该是可能的，因为装饰 View 不是数据驱动的。

Answer 1

我创建并测试了这个简单的例子，它似乎在所有可能的情况下都适用于 iOS 7(0 个部分，1 个部分有 0 个项目等)。这是我的布局类，UICollectionViewFlowLayout 的子类.该项目的其余部分只是脚手架。

#import "JKLayout.h"
#import "JKDecoration.h"

@implementation JKLayout

- (instancetype)init
{
    if (self = [super init]) {
        [self registerClass:[JKDecoration class] forDecorationViewOfKind:@"Decoration"];
    }
    return self;
}

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

    // It’s important to set indexPath to nil. If I had set it to indexPath 0-0, it crashed with InternalInconsistencyException
    // because I was trying to get decoration view for section 0 while there in reality was no section 0
    // I guess if you need to have several decoration views in this case, you’d identify them with a method other than indexpath
    return [allAttributes arrayByAddingObject:[self layoutAttributesForDecorationViewOfKind:@"Decoration" atIndexPath:nil]];
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString *)decorationViewKind atIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewLayoutAttributes *attr = [super layoutAttributesForDecorationViewOfKind:decorationViewKind atIndexPath:indexPath];
    if (!attr) {
        attr = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:decorationViewKind withIndexPath:indexPath];
        attr.frame = CGRectMake(0, 200, 100, 100);
    }
    return attr;
}

@end