自定义UICollectionViewLayout（适用于多个section）

一、自定义layout主要方法

　　重写系统的- (void)prepareLayout  方法；

　　其实就是计算每个cell的frame和其它相关属性。

　　

二、在网上看了好多自定义的layout 但是没有多section的，就整了这个……

　　全部代码：

.h文件

@class ForeverGuardFlowLayout;
@protocol ForeverGuardFlowLayoutDelegate <NSObject>
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(ForeverGuardFlowLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;
@end

@interface ForeverGuardFlowLayout : UICollectionViewFlowLayout

@property(nonatomic, assign)NSUInteger numberOfColumn;//列数
@property(nonatomic, assign)id<ForeverGuardFlowLayoutDelegate>delegate;

@end

 @interface ForeverGuardFlowLayout()
 //存放每一列的高度
 @property (nonatomic, retain) NSMutableArray *columnHeightsArray;

 //每个section的每一列的高度
 @property (nonatomic, retain) NSMutableArray *collectionHeightsArray;

 //存放每一个cell的属性
 @property (nonatomic, retain) NSMutableArray *attributesArray;

 @end
 @implementation  ForeverGuardFlowLayout

 /**
  每个区的最小高度

  @param section 区索引
  @return 高度
  */
 - (CGFloat)minHeightWithSection:(NSInteger)section{
     CGFloat min = ;
     for (NSNumber *height in _collectionHeightsArray[section]) {
         if (min > [height floatValue]) {
             min = [height floatValue];
         }
     }
     return min;
 }

 /**
  每个区的初始Y坐标

  @param section 区索引
  @return Y坐标
  */
 - (CGFloat)maxHeightWithSection:(NSInteger)section{

     if (section>) {
         CGFloat max = ;
         for (int i=; i<section; i++) {
             max += [self maxHeightAboutSection:_collectionHeightsArray[i]];
         }
         return max;
     }else{
         return ;
     }

 }

 /**
  每个区的最大高度

  @param dataArr 每个区的所有列的高度
  @return 最大高度
  */
 - (CGFloat)maxHeightAboutSection:(NSMutableArray *)dataArr{
     CGFloat max = ;
     for (NSNumber *heigth  in dataArr) {
         if (max < [heigth floatValue]) {
             max = [heigth floatValue];
         }
     }
     return max;

 }

 /**
  collectionView的显示高度
  */
 - (CGFloat)collectionHeight{
     CGFloat max = ;
     for (NSMutableArray *sectionArr in _collectionHeightsArray) {
         max += [self maxHeightAboutSection:sectionArr];
     }
     return max;
 }

 /**
  当前区的最小高度的索引

  @param section 当前区
  @return 最小高度的索引
  */
 - (NSUInteger)indexOfMinHeightWithSection:(NSInteger)section{
     NSUInteger index  = ;
     NSMutableArray *sectionArr = _collectionHeightsArray[section];
     for (int i=; i<sectionArr.count; i++) {
         CGFloat height = [sectionArr[i] floatValue];
         if (height == [self minHeightWithSection:section]) {
             index = i;
             return index;
         }
     }
     return index;
 }

 /**
  重写系统prepareLayout方法 （设置item的坐标等属性）
  */
 - (void)prepareLayout{
     [super prepareLayout];

     _attributesArray = [[NSMutableArray alloc] init];

     _columnHeightsArray = [NSMutableArray arrayWithCapacity:self.numberOfColumn];

     NSUInteger sectionCount = [self.collectionView numberOfSections];
     _collectionHeightsArray = [NSMutableArray arrayWithCapacity:sectionCount];

     for (int index = ; index<sectionCount; index++) {
         NSMutableArray *columnArr = [NSMutableArray array];
         for (int i=; i<self.numberOfColumn; i++) {
             [columnArr addObject:@0.0];
         }
         [_collectionHeightsArray addObject:columnArr];
     }

     CGFloat totalWidth = self.collectionView.frame.size.width;

     CGFloat x = ;
     CGFloat y = ;

     for (int index= ; index<sectionCount; index++) {
         NSUInteger  itemCount = [self.collectionView numberOfItemsInSection:index];
         x = ;
         y = [self maxHeightWithSection:index];
         for (int i=; i<itemCount; i++) {
             NSUInteger numberIfSoace = self.numberOfColumn-;
             CGFloat spaceWidth = 7.5;//item左右间距
             CGFloat width = (totalWidth - spaceWidth*numberIfSoace)/self.numberOfColumn;

             NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:index];

             CGSize imageSize =[self.delegate collectionView:self.collectionView layout:self sizeForItemAtIndexPath:indexPath];

             CGFloat height = width * imageSize.height / imageSize.width;

             UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];

             attributes.frame = CGRectMake(x, y, width, height);
             [_attributesArray addObject:attributes];

             NSUInteger minHeightIndex = [self indexOfMinHeightWithSection:index];

             CGFloat minHeight = [_collectionHeightsArray[index][minHeightIndex] floatValue];
             CGFloat lineHeight = 7.5;//item上下间距

             _collectionHeightsArray[index][minHeightIndex] = [NSNumber numberWithFloat:minHeight+lineHeight+height];
             minHeightIndex = [self indexOfMinHeightWithSection:index];

             x = (spaceWidth + width) * minHeightIndex;

             y += [self minHeightWithSection:index];

         }

     }

 }

 /**
  返回collectionView的界面显示大小
  */
 - (CGSize)collectionViewContentSize{
     return  CGSizeMake(self.collectionView.frame.size.width, [self collectionHeight]);
 }

 /**
  将所有的layoutAttributes重写布局
  */
 - (nullable NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect{
     return _attributesArray;
 }
 @end

.m文件

@interface ForeverGuardFlowLayout()
//存放每一列的高度
@property (nonatomic, retain) NSMutableArray *columnHeightsArray;
//每个section的每一列的高度
@property (nonatomic, retain) NSMutableArray *collectionHeightsArray;
//存放每一个cell的属性
@property (nonatomic, retain) NSMutableArray *attributesArray;

@end
@implementation  ForeverGuardFlowLayout

/**
 每个区的最小高度

 @param section 区索引
 @return 高度
 */
- (CGFloat)minHeightWithSection:(NSInteger)section{
    CGFloat min = ;
    for (NSNumber *height in _collectionHeightsArray[section]) {
        if (min > [height floatValue]) {
            min = [height floatValue];
        }
    }
    return min;
}

/**
 每个区的初始Y坐标

 @param section 区索引
 @return Y坐标
 */
- (CGFloat)maxHeightWithSection:(NSInteger)section{

    if (section>) {
        CGFloat max = ;
        for (int i=; i<section; i++) {
            max += [self maxHeightAboutSection:_collectionHeightsArray[i]];
        }
        return max;
    }else{
        return ;
    }

}

/**
 每个区的最大高度

 @param dataArr 每个区的所有列的高度
 @return 最大高度
 */
- (CGFloat)maxHeightAboutSection:(NSMutableArray *)dataArr{
    CGFloat max = ;
    for (NSNumber *heigth  in dataArr) {
        if (max < [heigth floatValue]) {
            max = [heigth floatValue];
        }
    }
    return max;

}

/**
 collectionView的显示高度
 */
- (CGFloat)collectionHeight{
    CGFloat max = ;
    for (NSMutableArray *sectionArr in _collectionHeightsArray) {
        max += [self maxHeightAboutSection:sectionArr];
    }
    return max;
}

/**
 当前区的最小高度的索引

 @param section 当前区
 @return 最小高度的索引
 */
- (NSUInteger)indexOfMinHeightWithSection:(NSInteger)section{
    NSUInteger index  = ;
    NSMutableArray *sectionArr = _collectionHeightsArray[section];
    for (int i=; i<sectionArr.count; i++) {
        CGFloat height = [sectionArr[i] floatValue];
        if (height == [self minHeightWithSection:section]) {
            index = i;
            return index;
        }
    }
    return index;
}

/**
 重写系统prepareLayout方法 （设置item的坐标等属性）
 */
- (void)prepareLayout{
    [super prepareLayout];
    _attributesArray = [[NSMutableArray alloc] init];
    _columnHeightsArray = [NSMutableArray arrayWithCapacity:self.numberOfColumn];
    NSUInteger sectionCount = [self.collectionView numberOfSections];
    _collectionHeightsArray = [NSMutableArray arrayWithCapacity:sectionCount];
    for (int index = ; index<sectionCount; index++) {
        NSMutableArray *columnArr = [NSMutableArray array];
        for (int i=; i<self.numberOfColumn; i++) {
            [columnArr addObject:@0.0];
        }
        [_collectionHeightsArray addObject:columnArr];
    }
    CGFloat totalWidth = self.collectionView.frame.size.width;

    CGFloat x = ;
    CGFloat y = ;

    for (int index= ; index<sectionCount; index++) {
        NSUInteger  itemCount = [self.collectionView numberOfItemsInSection:index];
        x = ;
        y = [self maxHeightWithSection:index];
        for (int i=; i<itemCount; i++) {
            NSUInteger numberIfSoace = self.numberOfColumn-;
            CGFloat spaceWidth = 7.5;//item左右间距
            CGFloat width = (totalWidth - spaceWidth*numberIfSoace)/self.numberOfColumn;
            NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:index];
            CGSize imageSize =[self.delegate collectionView:self.collectionView layout:self sizeForItemAtIndexPath:indexPath];
            CGFloat height = width * imageSize.height / imageSize.width;
            UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
            attributes.frame = CGRectMake(x, y, width, height);
            [_attributesArray addObject:attributes];

            NSUInteger minHeightIndex = [self indexOfMinHeightWithSection:index];
            CGFloat minHeight = [_collectionHeightsArray[index][minHeightIndex] floatValue];
            CGFloat lineHeight = 7.5;//item上下间距

            _collectionHeightsArray[index][minHeightIndex] = [NSNumber numberWithFloat:minHeight+lineHeight+height];
            minHeightIndex = [self indexOfMinHeightWithSection:index];

            x = (spaceWidth + width) * minHeightIndex;
            y = [self minHeightWithSection:index]+[self maxHeightWithSection:index];
        }
    }
}

/**
 返回collectionView的界面显示大小
 */
- (CGSize)collectionViewContentSize{
    return  CGSizeMake(self.collectionView.frame.size.width, [self collectionHeight]);
}

/**
 将所有的layoutAttributes重写布局
 */
- (nullable NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect{
    return _attributesArray;
}
@end