当系统给出的布局属性UIcollectionViewFlowLayout不能满足我们的需求的时候,我们就需要自己来定义一个我们需要的布局属性,来完成我们的需求,那么该怎么做呢?下面我将给出一个详细的demo给大家用参考,代码中均有详细的注释解释,希望对大家能有帮助.

//  XY_WaterFlowLayout.h
//  UI15_CustomCollectionViewLayout
//
//  Created by 岁变 on 16/8/3.
//  Copyright © 2016年 岁变. All rights reserved.
//

#import <UIKit/UIKit.h>

@protocol XY_WaterFlowLayoutDelegate <NSObject>

- (CGFloat)collectionView:(UICollectionView *)collectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
                   width:(CGFloat)width
heightForItemAtIndexPath:(NSIndexPath *)indexPath;
@end

//自定义布局继承于 UICollectionViewLayout

@interface XY_WaterFlowLayout : UICollectionViewLayout
@property (nonatomic, weak) id <XY_WaterFlowLayoutDelegate> delegate;

@property (nonatomic, assign) CGFloat itemWidth; //item的宽度
@property (nonatomic, assign) CGFloat horizontalSpace;//行间距
@property (nonatomic, assign) CGFloat verticalSpace;//竖向间距
@property (nonatomic, assign) UIEdgeInsets sectionInsets;//边距
@property (nonatomic, assign) NSInteger numberOfColumns; //列数

@end

//
//  XY_WaterFlowLayout.m
//  UI15_CustomCollectionViewLayout
//
//  Created by 岁变 on 16/8/3.
//  Copyright © 2016年 岁变. All rights reserved.
//

#import "XY_WaterFlowLayout.h"

@interface XY_WaterFlowLayout ()


@property (nonatomic, strong) NSMutableArray< UICollectionViewLayoutAttributes *> *attributesArrary; //保存布局属性的数组
@property (nonatomic, strong) NSMutableArray *arrHeightForColumns;//保存每列的高度

@property (nonatomic, assign) NSInteger shortestColumnsIndex; //最短列坐标
@property (nonatomic, assign) NSInteger longestColumnsIndex; //最长列坐标

@end

@implementation XY_WaterFlowLayout

- (instancetype)init {
    
    self = [super init];
    if (self) {
        //默认值 :列数2
        //      :横向间距10
        //      :纵向间距10
        //      :据四周边距 10 10 10 10
        _numberOfColumns = 2;
        _horizontalSpace = 10;
        _verticalSpace = 10;
        _sectionInsets = UIEdgeInsetsMake(10, 10, 10, 10);
    }
    return self;
}

- (CGFloat)itemWidth {
    
    self.itemWidth = (self.collectionView.frame.size.width - (_numberOfColumns - 1) * _horizontalSpace - _sectionInsets.left - _sectionInsets.right) / _numberOfColumns;
    return _itemWidth;
}


//自定义layout 必须重写三个方法

- (void)prepareLayout {
    [super prepareLayout];
    
    self.attributesArrary = [NSMutableArray array];
    self.arrHeightForColumns = [NSMutableArray array];
    //给每一列添加上边距的距离
    [self addTopSectionInsetsForColums];
    
    //获取item 的个数 [self.collectionView numberOfItemsInSection:0]
    for (int i = 0; i < [self.collectionView numberOfItemsInSection:0]; i++) {
        //为每个item创建布局属性 并添加到数组中
        UICollectionViewLayoutAttributes *layoutAttributes = [self setLayoutAttributesForItems:[NSIndexPath indexPathForItem:i inSection:0]];
        [_attributesArrary addObject:layoutAttributes];
    }
}

//返回每个item的布局属性
- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect {
    return _attributesArrary;
}

//负责滚动范围
- (CGSize)collectionViewContentSize {
    //获取最长列坐标
    NSInteger longextIndex = [self getLongestColumnsIndex];
    //获取最长列的长度
    CGFloat longestHeight = [_arrHeightForColumns[longextIndex] floatValue];
    //获取collectionView的size
    CGSize contentSize = self.collectionView.frame.size;
    contentSize.height = longestHeight + _sectionInsets.bottom;
    return contentSize;
}


//给每一刻加上上边距
- (void)addTopSectionInsetsForColums {
    
    for (int i = 0; i < _numberOfColumns; i++) {
        [_arrHeightForColumns addObject:@(_sectionInsets.top)];
    }
}




//生成每个item的不属性 主要是fram属性
- (UICollectionViewLayoutAttributes *)setLayoutAttributesForItems:(NSIndexPath *)indexPath {
    
    UICollectionViewLayoutAttributes *layoutAttributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    
    //item的原点坐标
    CGPoint origin = [self originForItem];
    
    //通过代理获取宽和高
    CGFloat height = 0;
    if ([self.delegate respondsToSelector:@selector(collectionView:layout:width:heightForItemAtIndexPath:)]) {
        height = [self.delegate collectionView:self.collectionView layout:self width:self.itemWidth heightForItemAtIndexPath:indexPath];
    }
    
    layoutAttributes.frame = CGRectMake(origin.x, origin.y, self.itemWidth, height);
    
    //更新数组里的列高度
    _arrHeightForColumns[_shortestColumnsIndex]  = @(origin.y + height);
    
    return layoutAttributes;

}

//计算原点坐标
- (CGPoint)originForItem {
    
    //最短列
    _shortestColumnsIndex = [self getShortestColumnsIndex];
    //计算原点坐标.x  左边距 + (item宽度 + item横向间距) * shorestColumnsIndex
    CGFloat x = _sectionInsets.left + (self.itemWidth + self.horizontalSpace) * _shortestColumnsIndex;
    
    //计算原点坐标.y
    CGFloat y = [_arrHeightForColumns[_shortestColumnsIndex] floatValue] + _verticalSpace;
    
    CGPoint origin = CGPointMake(x, y);
    return origin;
}


//记录最短列的坐标
- (NSInteger) getShortestColumnsIndex {
    //记录最短列
    NSInteger shortestIndex = 0;
    //记录最短高度
    CGFloat shortestHeight = MAXFLOAT;
    
    for (int i = 0; i < self.arrHeightForColumns.count; i++) {
        
        CGFloat currentHeight = [self.arrHeightForColumns[i] floatValue];
        if (currentHeight < shortestHeight) {
            shortestHeight = currentHeight;
            shortestIndex = i;
        }
    }
    return shortestIndex;
}

//记录最长列的坐标
- (NSInteger)getLongestColumnsIndex {
    //记录最长列
    NSInteger longestIndex = 0;
    //最长列高度
    CGFloat longestHight = 0;
    
    for (int i = 0; i < _arrHeightForColumns.count; i++) {
        CGFloat currentHeight = [self.arrHeightForColumns[i] floatValue];
        if (currentHeight > longestHight) {
            longestHight = currentHeight;
            longestIndex = i;
        }
    }
    return longestIndex;
}



@end