我正在尝试通过子类化 UICollectionViewFlowLayout 为 UICollectionView 定义自定义流布局。我想要的布局如下所示：
如您所见，我已将集合视图沿水平中间分隔线分成 2 行相等的行。顶行被分成三等分以给出 3 列，而底行被分成两半以给出 2 列。
一切似乎都正常工作并且看起来很好，直到您滚动到右侧（集合视图滚动到 UICollectionViewScrollDirectionHorizontal），并且在 5 个单元格完成渲染后看到有很大的空间：
我不知道为什么会发生这种情况，但是看起来空白空间看起来与顶行的单元格的宽度大致相同；集合视图宽度的三分之一。
这是我设置 UICollectionView 和 UICollectionViewFlowLayout 子类的方法
- (void)loadView {
[super loadView];
[self setupCollectionView];
}
- (void)setupCollectionView {
CustomFlowLayout *flowLayout = [[CustomFlowLayout alloc] init];
flowLayout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
flowLayout.minimumInteritemSpacing = 0.0;
flowLayout.minimumLineSpacing = 0.0f;
CGRect frame = CGRectMake(0, 0, 748, 1024);
UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:frame collectionViewLayout:flowLayout];
[collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:CollectionViewCellID];
collectionView.delegate = self;
collectionView.dataSource = self;
collectionView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
collectionView.backgroundColor = [UIColor whiteColor];
collectionView.pagingEnabled = YES;
self.collectionView = collectionView;
[self.view addSubview:self.collectionView];
}
#pragma mark - UICollectionViewDataSource
- (NSInteger )numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return 1;
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return 5;
}
集合视图中项目的大小由给定部分的布局配置定义，所以我这样实现collectionView:layout:sizeForItemAtIndexPath:：
- (CGSize)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout*)collectionViewLayout
sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
return [collectionViewLayout layoutAttributesForItemAtIndexPath:indexPath].size;
}
我的 UICollectionViewLayout 的自定义子类实现如下：
@implementation CustomFlowLayout
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
NSArray* attributesToReturn = [super layoutAttributesForElementsInRect:rect];
for (UICollectionViewLayoutAttributes* attributes in attributesToReturn) {
if (nil == attributes.representedElementKind) {
NSIndexPath* indexPath = attributes.indexPath;
attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame;
}
}
return attributesToReturn;
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes* currentItemAttributes = [super layoutAttributesForItemAtIndexPath:indexPath];
if (!currentItemAttributes) {
currentItemAttributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
}
float height = self.collectionView.frame.size.height;
float width = self.collectionView.frame.size.width;
CGRect frame = CGRectZero;
switch (indexPath.row) {
case 0:
frame.size = CGSizeMake(width/3, height/2);
frame.origin = CGPointMake(0, 0);
break;
case 1:
frame.size = CGSizeMake(width/3, height/2);
frame.origin = CGPointMake(width/3, 0);
break;
case 2:
frame.size = CGSizeMake(width/3, height/2);
frame.origin = CGPointMake(2*width/3, 0);
break;
case 3:
frame.size = CGSizeMake(width/2, height/2);
frame.origin = CGPointMake(0, height/2);
break;
case 4:
frame.size = CGSizeMake(width/2, height/2);
frame.origin = CGPointMake(width/2, height/2);
break;
default:
break;
}
currentItemAttributes.frame = frame;
currentItemAttributes.size = frame.size;
return currentItemAttributes;
}
任何人都知道为什么在渲染所有单元格后我有很大的空白空间？或者有没有人有更好的方法来渲染我所追求的布局。所有代码都可在此处作为示例 XCode 项目获得。非常感谢答案、提示、想法、请求请求。