LiedouYouxuan/YouHuiProject/YouHui/Home/ViewController/Today/View/TodayFlowLay.../LDTodayFlowL...

//
//  LDTodayFlowLayout.m
//  YouHuiProject
//
//  Created by 小花 on 2018/12/13.
//  Copyright © 2018年 kuxuan. All rights reserved.
//

#import "LDTodayFlowLayout.h"
#import "XHCollectionViewLayoutAttributes.h"
#import "XHCollectionReusableView.h"
@implementation LDTodayFlowLayout

NSString *const TodayCollectionViewSectionBackground = @"TodayCollectionViewSectionBackground";

#pragma mark ===============

-(instancetype)init
{
    self = [super init];
    if (self)
    {
        self.decorationViewAttrs = [NSMutableArray array];
        [self setup];
    }
    return self;
}

- (void)setup
{
    [self registerClass:[XHCollectionReusableView class] forDecorationViewOfKind:TodayCollectionViewSectionBackground];
}

- (void)prepareLayout
{
    [super prepareLayout];
    [self.decorationViewAttrs removeAllObjects];
    
    NSInteger numberOfSections = [self.collectionView numberOfSections];
    id delegate = self.collectionView.delegate;
    if (!numberOfSections || ![delegate conformsToProtocol:@protocol(TodayCollectionViewDelegateFlowLayout)]) {
        return;
    }
    
    for (NSInteger section = 0; section < numberOfSections; section++) {
        NSInteger numberOfItems = [self.collectionView numberOfItemsInSection:section];
        if (numberOfItems <= 0) {
            continue;
        }
        UICollectionViewLayoutAttributes *firstItem = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:section]];
        UICollectionViewLayoutAttributes *lastItem = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:numberOfItems - 1 inSection:section]];
        if (!firstItem || !lastItem) {
            continue;
        }
        
        UIEdgeInsets sectionInset = [self sectionInset];
        
        if ([delegate respondsToSelector:@selector(collectionView:layout:insetForSectionAtIndex:)]) {
            UIEdgeInsets inset = [delegate collectionView:self.collectionView layout:self insetForSectionAtIndex:section];
            sectionInset = inset;
        }
        
        
        CGRect sectionFrame = CGRectUnion(firstItem.frame, lastItem.frame);
        sectionFrame.origin.x -= sectionInset.left;
        sectionFrame.origin.y -= sectionInset.top;
        
        if (self.scrollDirection == UICollectionViewScrollDirectionHorizontal) {
            sectionFrame.size.width += sectionInset.left + sectionInset.right;
            sectionFrame.size.height = self.collectionView.frame.size.height;
        } else {
            sectionFrame.size.width = self.collectionView.frame.size.width;
            sectionFrame.size.height += sectionInset.top + sectionInset.bottom;
        }
        
        // 2、定义
        XHCollectionViewLayoutAttributes *attr = [XHCollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:TodayCollectionViewSectionBackground withIndexPath:[NSIndexPath indexPathForItem:0 inSection:section]];
        attr.frame = sectionFrame;
        attr.zIndex = -1;
        
        attr.backgroundColor = [delegate todayCollectionView:self.collectionView layout:self backgroundColorForSection:section];
        [self.decorationViewAttrs addObject:attr];
    }
    
}

- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSMutableArray *attrs = [[super layoutAttributesForElementsInRect:rect] mutableCopy];
    for (UICollectionViewLayoutAttributes *attr in self.decorationViewAttrs) {
        
        if (CGRectIntersectsRect(rect, attr.frame)) {
            [attrs addObject:attr];
        }
    }
    return attrs;
}


- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString*)elementKind atIndexPath:(NSIndexPath *)indexPath
{
    if ([elementKind isEqualToString:TodayCollectionViewSectionBackground]) {
        return [self.decorationViewAttrs objectAtIndex:indexPath.section];
    }
    return [super layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:indexPath];
}




@end