自定义UICollectionViewLayout(二) ----StackLayout&CircleLayout

layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath

@implementation HMStackLayout

/** 只要显示的边界发生改变就重新布局:
*  内部会重新调用layoutAttributesForElementsInRect方法获得所有的cell的布局属性
*/
- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
return YES;
}

- (CGSize)collectionViewContentSize
{
return CGSizeMake(500, 500);
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
NSArray *angles = @[@0, @(-0.2), @(-0.5), @(0.2), @(0.5)];
UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
attrs.size = CGSizeMake(100, 100);
attrs.center = CGPointMake(self.collectionView.frame.size.width * 0.5, self.collectionView.frame.size.height * 0.5);
if (indexPath.item>=5) {
attrs.hidden = YES;
} else {
attrs.transform = CGAffineTransformMakeRotation([angles[indexPath.item] floatValue]);
// zIndex越大,就越在上面
attrs.zIndex = [self.collectionView numberOfItemsInSection:indexPath.section] - indexPath.item;
}

return attrs;
}

- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSMutableArray *array = [NSMutableArray array];
NSInteger count = [self.collectionView numberOfItemsInSection:0];
for (int i = 0; i<count; i++) {
UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:i inSection:0]];
[array addObject:attrs];
}
return array;
}

@end

@implementation HMCircleLayout

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
return YES;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
attrs.size = CGSizeMake(100, 100);

// 圆的半径
CGFloat circleRadius = 150;
CGPoint circleCenter = CGPointMake(self.collectionView.frame.size.width * 0.5, self.collectionView.frame.size.height * 0.5);
// 每个item之间的角度
CGFloat angleDelta = M_PI * 2 / [self.collectionView numberOfItemsInSection:indexPath.section];
// 计算当前item的角度
CGFloat angle = indexPath.item * angleDelta;

attrs.center = CGPointMake(circleCenter.x + circleRadius * cosf(angle), circleCenter.y - circleRadius * sinf(angle));
return attrs;
}

- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSMutableArray *array = [NSMutableArray array];
NSInteger count = [self.collectionView numberOfItemsInSection:0];
for (int i = 0; i<count; i++) {
UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:i inSection:0]];
[array addObject:attrs];
}
return array;
}

@end