UICollectionViewLayout 自定义

//
//  PGGridLayout.m
//  TestCollectionView
//
//  Created by Yang Li on 2018/12/5.
//  Copyright © 2018 Qiekj. All rights reserved.
//

#import "PGGridLayout.h"

@interface PGGridLayout ()

@property(nonatomic, strong)NSArray *layoutInfoArray;
@property(nonatomic, assign)CGSize contentSize;

@end

@implementation PGGridLayout

- (instancetype)init {
    if (self = [super init]) {
        self.cellSpacing = 10;
        self.lineSpacing = 10;
        self.itemSize = CGSizeMake(100, 100);
    }
    return self;
}

- (void)setItemSize:(CGSize)itemSize {
    _itemSize = itemSize;
    [self invalidateLayout];
}

- (void)setLineSpacing:(CGFloat)lineSpacing {
    _lineSpacing = lineSpacing;
    [self invalidateLayout];
}

- (void)setCellSpacing:(CGFloat)cellSpacing {
    _cellSpacing = cellSpacing;
    [self invalidateLayout];
}

/**
 prepareLayout是专门用来准备布局的，
 在 prepareLayout 方法里面我们可以事先就计算后面要用到的布局信息并存储起来，
 防止后面方法多次计算，提高性能。例如，我们可以在此方法就计算好每个cell的属性、整个CollectionView的内容尺寸等等。
 此方法在布局之前会调用一次，之后只有在调用 invalidateLayout 、 shouldInvalidateLayoutForBoundsChange:
 返回 YES 和 UICollectionView刷新 的时候才会调用。
 */
- (void)prepareLayout {
    [super prepareLayout];
    NSMutableArray *layoutInfoArr = [NSMutableArray array];
    NSInteger maxNumberOfItems = 0;
    //获取布局信息
    NSInteger numberOfSections = [self.collectionView numberOfSections];
    for (NSInteger section = 0; section < numberOfSections; section++){
        NSInteger numberOfItems = [self.collectionView numberOfItemsInSection:section];
        NSMutableArray *subArr = [NSMutableArray arrayWithCapacity:numberOfItems];
        for (NSInteger item = 0; item < numberOfItems; item++){
            NSIndexPath *indexPath = [NSIndexPath indexPathForItem:item inSection:section];
            UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexPath];
            [subArr addObject:attributes];
        }
        if(maxNumberOfItems < numberOfItems){
            maxNumberOfItems = numberOfItems;
        }
        //添加到二维数组
        [layoutInfoArr addObject:[subArr copy]];
    }
    //存储布局信息
    self.layoutInfoArray = [layoutInfoArr copy];
    //保存内容尺寸
    self.contentSize = CGSizeMake(
                                  self.contentInset.left + self.contentInset.right + maxNumberOfItems * (self.itemSize.width + self.cellSpacing) + self.cellSpacing,
                                  self.contentInset.top + self.contentInset.bottom + numberOfSections * (self.itemSize.height + self.lineSpacing) + self.lineSpacing
                                  );
}

- (CGSize)collectionViewContentSize {
    return self.contentSize;
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{
    NSMutableArray *layoutAttributesArr = [NSMutableArray array];
    [self.layoutInfoArray enumerateObjectsUsingBlock:^(NSArray *array, NSUInteger i, BOOL * _Nonnull stop) {
        [array enumerateObjectsUsingBlock:^(UICollectionViewLayoutAttributes *obj, NSUInteger idx, BOOL * _Nonnull stop) {
            if(CGRectIntersectsRect(obj.frame, rect)) {
                [layoutAttributesArr addObject:obj];
            }
        }];
    }];
    return layoutAttributesArr;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{
    UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    //每一组cell为一行
    attributes.frame = CGRectMake(
                                  self.contentInset.left + (self.itemSize.width + self.cellSpacing) * indexPath.row + self.cellSpacing,
                                  self.contentInset.top + (self.itemSize.height + self.lineSpacing) * indexPath.section + self.lineSpacing,
                                  self.itemSize.width,
                                  self.itemSize.height
                                  );
    return attributes;
}

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

@end

//
//  PGGridLayout.h
//  TestCollectionView
//
//  Created by Yang Li on 2018/12/5.
//  Copyright © 2018 Qiekj. All rights reserved.
//

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface PGGridLayout : UICollectionViewLayout

//每个cell 大小
@property(nonatomic, assign)CGSize itemSize;
//每个cell 间的距离
@property(nonatomic, assign)CGFloat cellSpacing;
//一行间距
@property(nonatomic, assign)CGFloat lineSpacing;
//内边距
@property(nonatomic, assign)UIEdgeInsets contentInset;

@end

NS_ASSUME_NONNULL_END