空集合視圖中的UICollectionView裝飾

Question

我已經實現了具有自定義佈局的UICollectionView。它爲佈局添加了裝飾視圖。我用下面的代碼來添加裝飾視圖的佈局屬性：

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

在集合視圖的數據由一個NSFetchedResultsController提供。

現在它看起來喜歡它工作得很好，但是當集合視圖是空的，因爲有試圖使用它沒有索引路區間爲0，但失敗也失敗了。有關如何在空的UICollectionView中使用裝飾視圖的任何想法？由於裝飾視圖不是數據驅動的，因此應該是可能的。

Answer 1

我創建並測試了這個簡單的例子，它似乎可以在所有可能的情況下工作在iOS 7中（0節，1節0節等）。這是我的佈局類，UICollectionViewFlowLayout的子類。該項目的其餘部分只是腳手架。

#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 

Answer 2

當使用裝飾視圖或沒有連接到特定小區的補充視圖中，使用[NSIndexPath indexPathWithIndex:]指定索引路徑。下面是一個示例代碼：

@interface BBCollectionViewLayout : UICollectionViewFlowLayout 

@end 

@implementation BBCollectionViewLayout 

- (void)BBCollectionViewLayout_commonInit { 
    [self registerClass:[BBCollectionReusableView class] forDecorationViewOfKind:BBCollectionReusableViewKind]; 
} 

- (id)initWithCoder:(NSCoder *)aDecoder { 
    if ((self = [super initWithCoder:aDecoder])) { 
     [self BBCollectionViewLayout_commonInit]; 
    } 
    return self; 
} 

- (id)init { 
    self = [super init]; 
    if (self) { 
     [self BBCollectionViewLayout_commonInit]; 
    } 
    return self; 
} 

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

    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForDecorationViewOfKind:BBCollectionReusableViewKind atIndexPath:[NSIndexPath indexPathWithIndex:0]]; 

    if (CGRectIntersectsRect(rect, attributes.frame)) { 
     [array addObject:attributes]; 
    } 

    return array; 
} 

- (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString*)elementKind atIndexPath:(NSIndexPath *)indexPath { 
    UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:elementKind withIndexPath:indexPath]; 
    attributes.frame = CGRectMake(0., 60., 44., 44.); 
    return attributes; 
} 

@end