自定义UICollectionLayout

#import "AppDelegate.h"
#import "CircleLayout.h"
#import "CollectionViewDataSource.h"
#import "MyCollectionReusableView.h"

@interface CircleLayout()
{
CGSize cvSize;
CGPoint cvCenter;
CGFloat radius;
NSInteger cellCount;
}

@property (strong, nonatomic) NSMutableArray *indexPathsToAnimate;

@end

@implementation CircleLayout

- (void)prepareLayout
{
[super prepareLayout];

[self registerClass:[MyCollectionReusableView class] forDecorationViewOfKind:@"MyDecoration"];

cvSize = self.collectionView.frame.size;
cellCount = [self.collectionView numberOfItemsInSection:0];
cvCenter = CGPointMake(cvSize.width / 2.0, cvSize.height / 2.0);
radius = MIN(cvSize.width, cvSize.height) / 2.5;
}

- (CGSize)collectionViewContentSize
{
return self.collectionView.bounds.size;
}

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

//add cells
for (int i=0; i<cellCount; i++)
{
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];

UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexPath];

[array addObject:attributes];
}

//add first supplementaryView
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:@"FirstSupplementary" atIndexPath:indexPath];
[array addObject:attributes];

//add second supplementaryView
attributes = [self layoutAttributesForSupplementaryViewOfKind:@"SecondSupplementary" atIndexPath:indexPath];
[array addObject:attributes];

//add decorationView
attributes = [self layoutAttributesForDecorationViewOfKind:@"MyDecoration" atIndexPath:indexPath];
[array addObject:attributes];

return array;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];

attributes.size = CGSizeMake(20, 20);
attributes.center = CGPointMake(cvCenter.x + radius * cosf(2 * indexPath.item * M_PI / cellCount),
cvCenter.y + radius * sinf(2 * indexPath.item * M_PI / cellCount));

return attributes;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForSupplementaryViewOfKind:elementKind withIndexPath:indexPath];

attributes.size = CGSizeMake(260, 40);
if([elementKind isEqual:@"FirstSupplementary"])
{
attributes.center = CGPointMake(cvSize.width/2, 40);
}
else
{
attributes.center = CGPointMake(cvSize.width/2, cvSize.height-40);
}

return attributes;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:elementKind withIndexPath:indexPath];

attributes.size = CGSizeMake(140, 40);
attributes.center = CGPointMake(cvSize.width/2, cvSize.height/2);

return attributes;
}

//当边界更改时是否更新布局
- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
CGRect oldBounds = self.collectionView.bounds;

if (CGRectGetWidth(newBounds) != CGRectGetWidth(oldBounds))
{
return YES;
}

return NO;
}

//通知布局，collection view里有元素即将改变，这里可以收集改变的元素indexPath和action类型。
-(void)prepareForCollectionViewUpdates:(NSArray *)updateItems
{
[super prepareForCollectionViewUpdates:updateItems];

NSMutableArray *indexPaths = [NSMutableArray array];

for(UICollectionViewUpdateItem *updateItem in updateItems)
{
//UICollectionUpdateActionInsert,
//UICollectionUpdateActionDelete,
//UICollectionUpdateActionReload,
//UICollectionUpdateActionMove,
//UICollectionUpdateActionNone

NSLog(@"before index:%d,after index:%d,action:%d", updateItem.indexPathBeforeUpdate.row,updateItem.indexPathAfterUpdate.row,updateItem.updateAction);

switch (updateItem.updateAction) {
case UICollectionUpdateActionInsert:
[indexPaths addObject:updateItem.indexPathAfterUpdate];
break;
case UICollectionUpdateActionDelete:
[indexPaths addObject:updateItem.indexPathBeforeUpdate];
break;
case UICollectionUpdateActionMove:
[indexPaths addObject:updateItem.indexPathBeforeUpdate];
[indexPaths addObject:updateItem.indexPathAfterUpdate];
break;
default:
NSLog(@"unhandled case: %@", updateItem);
break;
}
}

self.indexPathsToAnimate = indexPaths;
}

//当一个元素被插入collection view时，返回它的初始布局，这里可以加入一些动画效果。
- (UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
{
UICollectionViewLayoutAttributes *attr = [self layoutAttributesForItemAtIndexPath:itemIndexPath];

if([self.indexPathsToAnimate containsObject:itemIndexPath])
{
attr.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(10,10),M_PI);
attr.center = CGPointMake(CGRectGetMidX(self.collectionView.bounds), CGRectGetMidY(self.collectionView.bounds));
[self.indexPathsToAnimate removeObject:itemIndexPath];
}

return attr;
}

- (NSArray *)getLetterArray
{
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];

return appDelegate.letterArray;
}

@end

CircleLayout.m