自定义UICollectionLayout

1.自定义flowLayout

注 ：自定义的时候继承UICollectionViewFlowLayout,可以保存流水布局的效果

属性介绍 UICollectionViewLayoutAttributes

NS_CLASS_AVAILABLE_IOS(6_0) @interface UICollectionViewLayoutAttributes : NSObject 

@property (nonatomic) CGRect frame;
@property (nonatomic) CGPoint center;
@property (nonatomic) CGSize size;
@property (nonatomic) CATransform3D transform3D;
@property (nonatomic) CGRect bounds NS_AVAILABLE_IOS(7_0);
@property (nonatomic) CGAffineTransform transform NS_AVAILABLE_IOS(7_0);
@property (nonatomic) CGFloat alpha;
@property (nonatomic) NSInteger zIndex; // default is 0
@property (nonatomic, getter=isHidden) BOOL hidden; // As an optimization, UICollectionView might not create a view for items whose hidden attribute is YES
@property (nonatomic, retain) NSIndexPath *indexPath;

@property (nonatomic, readonly) UICollectionElementCategory representedElementCategory;
@property (nonatomic, readonly) NSString *representedElementKind; // nil when representedElementCategory is UICollectionElementCategoryCell

+ (instancetype)layoutAttributesForCellWithIndexPath:(NSIndexPath *)indexPath;
+ (instancetype)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind withIndexPath:(NSIndexPath *)indexPath;
+ (instancetype)layoutAttributesForDecorationViewOfKind:(NSString *)decorationViewKind withIndexPath:(NSIndexPath*)indexPath;

@end

注 ：zIndex指的是在层次上的先后顺序，在做相册效果的时候可以使得层次效果发生改变
可以看到关于cell的所有属性的信息，可以通过对transform3D或者transform的处理达到需要的动画效果

方法介绍

- (void)prepareLayout;
介绍：准备布局信息，官方给的介绍中提到Subclasses should always call super if they override.最好把对于layout的frame的定义写到这里

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds;
介绍：只要UICollectionView的边界发生了改变就会调用这个方法，内部会重新调用prepareLayout和layoutAttributesForElementsInRect方法获得所有cell的布局属性，所有是重新定义layout必须实现的方法

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect;
介绍：拿到所有UICollectionView中的UICollectionViewLayoutAttributes信息，可以通过CGRectIntersectsRect方法判断出屏幕上正在显示cell、header、footer的布局信息

自定义JXFlowLayout

#import "JXFlowLayout.h"

static CGFloat const velocityX = 2.5;

@implementation JXFlowLayout

//做好准备
- (void)prepareLayout
{
    [super prepareLayout];
    
    CGFloat itenWidth = 150;
    self.itemSize = CGSizeMake(itenWidth, itenWidth);
    self.minimumLineSpacing = itenWidth * 0.3;
    self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    CGFloat sectionBeginLocation = (self.collectionView.frame.size.width - self.itemSize.width) * 0.5;
    self.sectionInset = UIEdgeInsetsMake(0, sectionBeginLocation, 0, sectionBeginLocation);
}

//一旦边界改变就刷新
- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
    return YES;
}

/** 有效距离:当item的中间x距离屏幕的中间x在JXActiveDistance以内,才会开始放大, 其它情况都是缩小 */
static CGFloat const JXActiveDistance = 150;
/** 缩放因素: 值越大, item就会越大 */
static CGFloat const JXScaleFactor = 0.6;

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *array = [super layoutAttributesForElementsInRect:rect];
    for (UICollectionViewLayoutAttributes *attributes in array) {
        
        //拿到在当前屏幕中的部分
        CGRect currentBounds ;
        currentBounds.origin = self.collectionView.contentOffset;
        currentBounds.size = self.collectionView.frame.size;
        
        //屏幕中间的部分需要进行缩放处理
        if (!CGRectIntersectsRect(currentBounds, attributes.frame)) continue;
        
        CGFloat centerX = self.collectionView.contentOffset.x + self.collectionView.frame.size.width * 0.5;
        // 每一个item的中点x
        CGFloat itemCenterX = attributes.center.x;
        
        // 差距越小, 缩放比例越大
        // 根据跟屏幕最中间的距离计算缩放比例
        CGFloat scale = 1 + JXScaleFactor * (1 - (ABS(itemCenterX - centerX) / JXActiveDistance));
        attributes.transform = CGAffineTransformMakeScale(scale, scale);
    }
    
    return array;
}

- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
{
// 1.计算出scrollView最后会停留的范围
    CGRect lastRect;
    //    lastRect.origin = proposedContentOffset;
    // lastRect.origin = self.collectionView.contentOffset;
    // 这里是根据滑动速度的一个配置，如果速度够大，就采用预计停留的点作为起始点，否则采用当前屏幕的点作为起始点
    if (ABS(velocity.x) > velocityX) {
         lastRect.origin = proposedContentOffset;
         
     }else{
         lastRect.origin = self.collectionView.contentOffset;
     }

    lastRect.size = self.collectionView.frame.size;
    
    // 计算屏幕�最中间的x
    CGFloat centerX = proposedContentOffset.x + self.collectionView.frame.size.width * 0.5;
    
    // 2.取出这个范围内的所有属性
    NSArray *array = [self layoutAttributesForElementsInRect:lastRect];
    
    // 3.遍历所有属性
    CGFloat adjustOffsetX = MAXFLOAT;
    for (UICollectionViewLayoutAttributes *attrs in array) {
        if (ABS(attrs.center.x - centerX) < ABS(adjustOffsetX)) {
            adjustOffsetX = attrs.center.x - centerX;
        }
    }
    return CGPointMake(proposedContentOffset.x + adjustOffsetX, proposedContentOffset.y);
}

转发一个自定义的停留效果：XLPlainFlowLayout

2.自定义Layout

方法介绍

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;
介绍： 实现对于每个indexPath的cell的布局信息
- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;
介绍：对于header和footer的布局（如果没有，可不重载）
- (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString*)elementKind atIndexPath:(NSIndexPath *)indexPath;
介绍：对于装饰视图的布局（如果没有，可不重载）
一个简单的相册叠加布局

@implementation JXStackLayout

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

//- (CGSize)collectionViewContentSize
//{
//    return CGSizeMake(500, 500);
//}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSArray *angles = @[@0, @(-0.2), @(-0.5), @(0.2), @(0.5)];
    UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    attrs.size = CGSizeMake(100, 100);
    attrs.center = CGPointMake(self.collectionView.frame.size.width * 0.5, self.collectionView.frame.size.height * 0.5);
    if (indexPath.item >= 5) {
        attrs.hidden = YES;
    } else {
        attrs.transform = CGAffineTransformMakeRotation([angles[indexPath.item] floatValue]);
        // zIndex越大,就越在上面
        attrs.zIndex = [self.collectionView numberOfItemsInSection:indexPath.section] - indexPath.item;
    }
    return attrs;
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSMutableArray *array = [NSMutableArray array];
    NSInteger count = [self.collectionView numberOfItemsInSection:0];
    for (int i = 0; i

瀑布流

@class JXWaterflowLayout;
@protocol JXWaterflowLayoutDelegate 
- (CGFloat)waterflowLayout:(JXWaterflowLayout *)waterflowLayout heightForWidth:(CGFloat)width atIndexPath:(NSIndexPath *)indexPath;
@end

@interface JXWaterflowLayout : UICollectionViewLayout
@property (nonatomic, assign) UIEdgeInsets sectionInset;
/** 每一列之间的间距 */
@property (nonatomic, assign) CGFloat columnMargin;
/** 每一行之间的间距 */
@property (nonatomic, assign) CGFloat rowMargin;
/** 显示多少列 */
@property (nonatomic, assign) int columnsCount;
@property (nonatomic, weak) id delegate;
@end

#import "JXWaterflowLayout.h"

//static const CGFloat JXColumnMargin = 10;
//static const CGFloat JXRowMargin = JXColumnMargin;

@interface JXWaterflowLayout();
/** 这个字典用来存储每一列最大的Y值(每一列的高度) */
@property (nonatomic, strong) NSMutableDictionary *maxYDict;

/** 存放所有的布局属性 */
@property (nonatomic, strong) NSMutableArray *attrsArray;
@end

@implementation JXWaterflowLayout

- (NSMutableDictionary *)maxYDict
{
    if (!_maxYDict) {
        self.maxYDict = [[NSMutableDictionary alloc] init];
    }
    return _maxYDict;
}

- (NSMutableArray *)attrsArray
{
    if (!_attrsArray) {
        self.attrsArray = [[NSMutableArray alloc] init];
    }
    return _attrsArray;
}

- (instancetype)init
{
    if (self = [super init]) {
        self.columnMargin = 10;
        self.rowMargin = 10;
        self.sectionInset = UIEdgeInsetsMake(10, 10, 10, 10);
        self.columnsCount = 3;
    }
    return self;
}

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

/**
 *  每次布局之前的准备
 */
- (void)prepareLayout
{
    [super prepareLayout];
    
    // 1.清空最大的Y值
    for (int i = 0; i [self.maxYDict[maxColumn] floatValue]) {
            maxColumn = column;
        }
    }];
    return CGSizeMake(0, [self.maxYDict[maxColumn] floatValue] + self.sectionInset.bottom);
}

/**
 *  返回indexPath这个位置Item的布局属性
 */
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    // 假设最短的那一列的第0列
    __block NSString *minColumn = @"0";
    // 找出最短的那一列
    [self.maxYDict enumerateKeysAndObjectsUsingBlock:^(NSString *column, NSNumber *maxY, BOOL *stop) {
        if ([maxY floatValue] < [self.maxYDict[minColumn] floatValue]) {
            minColumn = column;
        }
    }];
    
    // 计算尺寸
    CGFloat width = (self.collectionView.frame.size.width - self.sectionInset.left - self.sectionInset.right - (self.columnsCount - 1) * self.columnMargin)/self.columnsCount;
    CGFloat height = [self.delegate waterflowLayout:self heightForWidth:width atIndexPath:indexPath];
    
    // 计算位置
    CGFloat x = self.sectionInset.left + (width + self.columnMargin) * [minColumn intValue];
    CGFloat y = [self.maxYDict[minColumn] floatValue] + self.rowMargin;
    
    // 更新这一列的最大Y值
    self.maxYDict[minColumn] = @(y + height);
    
    // 创建属性
    UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    attrs.frame = CGRectMake(x, y, width, height);
    return attrs;
}

/**
 *  返回rect范围内的布局属性
 */
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    return self.attrsArray;
}