Kulexiu/KulexiuForStudent/KulexiuForStudent/Module/Home/View/HomePageView/TeacherStyleFlowLayout.m

//
//  TeacherStyleFlowLayout.m
//  KulexiuForStudent
//
//  Created by 王智 on 2022/8/30.
//

#import "TeacherStyleFlowLayout.h"

@interface TeacherStyleFlowLayout ()

/** 这个字典用来存储每一列item的高度 */
@property (strong,nonatomic)NSMutableDictionary *maxYDic;
/** 存放每一个item的布局属性 */
@property (strong,nonatomic)NSMutableArray *attrsArray;

@end

@implementation TeacherStyleFlowLayout

- (instancetype)init {
    if (self = [super init]){
        self.columnMargin = 12;
        self.rowMargin = 11;
        self.columnCount = 2;
    }
    return self;
}

//每一次布局前的准备工作
-(void)prepareLayout
{
    [super prepareLayout];
    
    //清空最大的y值
    for (int i =0; i < self.columnCount; i++)
    {
        NSString *column = [NSString stringWithFormat:@"%d",i];
        self.maxYDic[column] = @(self.sectionInset.top);
    }

    //计算所有item的属性
    [self.attrsArray removeAllObjects];
    NSInteger count = [self.collectionView numberOfItemsInSection:0];
    for (int i=0; i<count; i++)
    {
        UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:i inSection:0]];
        [self.attrsArray addObject:attrs];
    }
}

//设置collectionView滚动区域
- (CGSize)collectionViewContentSize
{
    //假设最长的那一列为第0列
    __block NSString *maxColumn = @"0";
    
    //遍历字典,找出最长的那一列
    [self.maxYDic enumerateKeysAndObjectsUsingBlock:^(NSString *column, NSNumber *maxY, BOOL *stop) {
        
        if ([maxY floatValue] > [self.maxYDic[maxColumn] floatValue])
        {
            maxColumn = column;
        }
    }];
    return CGSizeMake(0, [self.maxYDic[maxColumn]floatValue]+self.sectionInset.bottom);
}

//允许每一次重新布局
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
    return YES;
}

//布局每一个属性
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    //假设最短的那一列为第0列
    __block NSString *minColumn = @"0";
    
    //遍历字典,找出最短的那一列
    [self.maxYDic enumerateKeysAndObjectsUsingBlock:^(NSString *column, NSNumber *maxY, BOOL *stop) {
        
        if ([maxY floatValue] < [self.maxYDic[minColumn] floatValue])
        {
            minColumn = column;
        }
    }];
    
    //计算每一个item的宽度和高度
    CGFloat width = (self.collectionView.frame.size.width - self.columnMargin*(self.columnCount - 1) - self.sectionInset.left - self.sectionInset.right) / self.columnCount;
    
    CGFloat height = [self.delegate waterFlowLayout:self heightForWidth:width andIndexPath:indexPath] ;
    
    
    //计算每一个item的位置
    CGFloat x = self.sectionInset.left + (width + self.columnMargin) * [minColumn floatValue];
    CGFloat y = [self.maxYDic[minColumn] floatValue] + self.rowMargin;
    
    
    //更新这一列的y值
    self.maxYDic[minColumn] = @(y + height);
    
    
    //创建布局属性
    UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    
    //设置item的frame
    attrs.frame = CGRectMake(x, y, width, height);
    
    return attrs;
}

//布局所有item的属性,包括header、footer
-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    return self.attrsArray;
}

#pragma mark ---- lazying
- (NSMutableDictionary *)maxYDic {
    if (!_maxYDic) {
        _maxYDic = [NSMutableDictionary dictionary];
    }
    return _maxYDic;
}

- (NSMutableArray *)attrsArray {
    if (!_attrsArray) {
        _attrsArray = [NSMutableArray array];
    }
    return _attrsArray;
}

@end