效果：
运行效果
1.首先要先继承UICollectionReusableView 的一个view ，collectionview背景图是UICollectionReusableView子类；里面实现自定义效果如下：
自定义背景图
2.自定义collectionLayout关键在于layout中的实现计算frame
#importstatic NSString * const DZSetSectionBack = @"ccDecoration";@protocol DZSetSectionBackgroundLayoutDelegate@required-(UIEdgeInsets)cccollectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;-(CGSize)cccollectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout headerForSectionAtIndex:(NSInteger)section;@optional-(CGSize)cccollectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout footerForSectionAtIndex:(NSInteger)section;@end@interface DZSetSectionBackground : UICollectionViewFlowLayout@property (nonatomic, assign)idmydelegate;
@end
#import "DZSetSectionBackground.h"
#import "DZMyBackReusableView.h"
#import "Header.h"
@interface DZSetSectionBackground ()
/**
存储 布局的 att
*/
@property (nonatomic,strong) NSMutableArray *layoutInfoArr;
/**
collection 滑动区域大小
*/
@property (nonatomic,assign) CGSize contentSize;
@end
@implementation DZSetSectionBackground
/**
布局 布局配置数据 布局前的准备会调用这个方法
*/
- (void)prepareLayout{
[super prepareLayout];
//获取布局信息
[self registerClass:[DZMyBackReusableView class] forDecorationViewOfKind:DZSetSectionBack];
[self.layoutInfoArr removeAllObjects];
CGRect tmpsectionFrame = CGRectZero;
NSInteger numberOfSections = [self.collectionView numberOfSections];
for (NSInteger section = 0; section < numberOfSections; section++){
NSInteger num = [self.collectionView numberOfItemsInSection:section];
UICollectionViewLayoutAttributes *first = nil;//组第一个 item att
UICollectionViewLayoutAttributes *last = nil;//组最后一个 item att
if (num>0) {
first = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:section]];
last = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForRow:num-1 inSection:section]];
}
UIEdgeInsets sectionInset = self.sectionInset;
UIEdgeInsets inset = [self.mydelegate cccollectionView:self.collectionView layout:self insetForSectionAtIndex:section];
if (!UIEdgeInsetsEqualToEdgeInsets(inset, UIEdgeInsetsZero)) {
sectionInset = inset;
}
CGSize headerSize = [self.mydelegate cccollectionView:self.collectionView layout:self headerForSectionAtIndex:section];
// CGSize footerSize = [self.mydelegate cccollectionView:self.collectionView layout:self footerForSectionAtIndex:section];
CGRect sectionFrame = CGRectZero;
if (self.scrollDirection == UICollectionViewScrollDirectionHorizontal) {
sectionFrame = CGRectMake(CGRectGetMinX(first.frame)-headerSize.width+sectionInset.left, CGRectGetMinY(first.frame)+sectionInset.top, CGRectGetMaxX(last.frame)-sectionInset.right, CGRectGetMaxY(last.frame)-sectionInset.bottom);
sectionFrame.origin.y = sectionInset.top;
sectionFrame.size.width = sectionFrame.size.width-sectionFrame.origin.x;
sectionFrame.size.height = CGRectGetHeight(self.collectionView.frame)-sectionInset.top-sectionInset.bottom;
} else {
sectionFrame = CGRectMake(CGRectGetMinX(first.frame), CGRectGetMinY(first.frame)-headerSize.height+sectionInset.top, CGRectGetMaxX(last.frame), CGRectGetMaxY(last.frame)-sectionInset.bottom);
sectionFrame.origin.x = sectionInset.left;
sectionFrame.size.width = CGRectGetWidth(self.collectionView.frame)-sectionInset.left-sectionInset.right;
sectionFrame.size.height = sectionFrame.size.height-sectionFrame.origin.y;
}
UICollectionViewLayoutAttributes *att = [self layoutAttributesForDecorationViewOfKind:DZSetSectionBack atIndexPath:[NSIndexPath indexPathForRow:0 inSection:section]];
att.frame = sectionFrame;
att.zIndex = -1;
att.hidden = NO;
[self.layoutInfoArr addObject:att];
tmpsectionFrame = sectionFrame;
}
}
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{
NSArray *arr = [super layoutAttributesForElementsInRect:rect];
NSMutableArray *rt = [NSMutableArray array];
[rt addObjectsFromArray:arr];
for (UICollectionViewLayoutAttributes *att in self.layoutInfoArr) {
if (CGRectIntersectsRect(att.frame, rect)) {
[rt addObject:att];
}
}
return rt;
}
-(NSMutableArray *)layoutInfoArr{
if (_layoutInfoArr==nil) {
_layoutInfoArr = [NSMutableArray array];
}
return _layoutInfoArr;
}
-(UICollectionViewLayoutAttributes*)layoutAttributesForDecorationViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath{
UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:elementKind withIndexPath:indexPath];
return attrs;
}
@end
3.demo下载：github.com/C100515C/CollectionCustomBackgroud.git
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