我正在实现自定义流布局。它有2种主要的方法可以覆盖以确定单元格的位置:layoutAttributesForElementsInRect
和layoutAttributesForItemAtIndexPath
。
在我的代码中,layoutAttributesForElementsInRect
被调用,但是layoutAttributesForItemAtIndexPath
没有被调用。什么决定哪个被调用? layoutAttributesForItemAtIndexPath
在哪里调用?
最佳答案
layoutAttributesForElementsInRect:
不一定调用layoutAttributesForItemAtIndexPath:
。
实际上,如果您子类UICollectionViewFlowLayout
,则流布局将准备布局并缓存结果属性。因此,当调用layoutAttributesForElementsInRect:
时,它不会询问layoutAttributesForItemAtIndexPath:
,而只会使用缓存的值。
如果要确保始终根据布局修改布局属性,请为layoutAttributesForElementsInRect:
和layoutAttributesForItemAtIndexPath:
都实现一个修饰符:
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSArray *attributesInRect = [super layoutAttributesForElementsInRect:rect];
for (UICollectionViewLayoutAttributes *cellAttributes in attributesInRect) {
[self modifyLayoutAttributes:cellAttributes];
}
return attributesInRect;
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewLayoutAttributes *attributes = [super layoutAttributesForItemAtIndexPath:indexPath];
[self modifyLayoutAttributes:attributes];
return attributes;
}
- (void)modifyLayoutAttributes:(UICollectionViewLayoutAttributes *)attributes
{
// Adjust the standard properties size, center, transform etc.
// Or subclass UICollectionViewLayoutAttributes and add additional attributes.
// Note, that a subclass will require you to override copyWithZone and isEqual.
// And you'll need to tell your layout to use your subclass in +(Class)layoutAttributesClass
}
关于ios - UICollectionViewLayout layoutAttributesForElementsInRect和layoutAttributesForItemAtIndexPath,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/24490841/