我正在实现自定义流布局.它有两种主要的重写方法来确定单元格的布局：layoutAttributesForElementsInRect和layoutAttributesForItemAtIndexPath.
在我的代码中,调用layoutAttributesForElementsInRect,但是layoutAttributesForItemAtIndexPath不是.什么决定哪个被叫？ layoutAttributesForItemAtIndexPath在哪里被调用？
解决方法
layoutAttributesForElementsInRect：不一定调用layoutAttributesForItemAtIndexPath :.
实际上,如果你的UICollectionViewFlowLayout子类化,流布局将准备布局并缓存生成的属性.所以当layoutAttributesForElementsInRect：被调用时,它不会要求layoutAttributesForItemAtIndexPath：,而只是使用缓存的值.
如果要确保布局属性总是根据布局进行修改,请为layoutAttributesForElementsInRect：和layoutAttributesForItemAtIndexPath ::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
- }
