瀑布流学习、 点击状态栏返回顶部、 点击按钮返回顶部、Label透明度字体跟着变浅的解决方法

self.dict enumerateKeysAndObjectsUsingBlocking:^(NSString *key, NSNumber *maxY, BOOL *stop){

   };

———————————————————————————————瀑布流———————————

#import <UIKit/UIKit.h>
@class CKWaterFlowLayout;
// 唯一的代理方法
@protocol CKWaterFlowLayoutDelegate <NSObject>
- (CGFloat)waterFlowLayout:(CKWaterFlowLayout *)waterFlowLayout heightForWidth:(CGFloat)width atIndexPath:(NSIndexPath *)indexPath;
@end

@interface CKWaterFlowLayout : UICollectionViewLayout
@property (nonatomic,assign)UIEdgeInsets sectionInset; // 内边距
@property (nonatomic,assign)CGFloat columnMargin; // 每一列之间的间距
@property (nonatomic,assign)CGFloat rowMargin; // 每一行之间的间距
@property (nonatomic,assign)int columnsCount; // 显示多少列

@property (nonatomic,weak) id<CKWaterFlowLayoutDelegate> delegate;

@end

// 瀑布流使用指南
/**
 - (void)addCollectionView
 {
 CKWaterFlowLayout *layout = [[CKWaterFlowLayout alloc]init];
 layout.delegate = self;
 layout.sectionInset = UIEdgeInsetsMake(10, 10, 10, 10);
 layout.columnMargin = 10;
 layout.rowMargin = 10;
 layout.columnsCount = 3;
 self.collectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) collectionViewLayout:layout];
 self.collectionView.dataSource = self;
 self.collectionView.delegate = self;
 [self.collectionView registerNib:[UINib nibWithNibName:@"WaterFlowCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"WaterFlowCollectionViewCell"];
 self.collectionView.backgroundColor = [UIColor whiteColor];
 [self.view addSubview:self.collectionView];
 }
 
 #pragma mark -- CKwaterFlowLayoutDelegate
 - (CGFloat)waterFlowLayout:(CKWaterFlowLayout *)waterFlowLayout heightForWidth:(CGFloat)width atIndexPath:(NSIndexPath *)indexPath
 {
 ImageModel *model = self.dataArray[indexPath.item];
 return model.y / model.x *width;
 }

 */

#import "CKWaterFlowLayout.h"

@interface CKWaterFlowLayout()

// 这个字典用来存放每一列最大的Y值（每一列的高度）
@property (nonatomic,retain)NSMutableDictionary *maxYDict;
// 用来存放所有的布局属性
@property (nonatomic,retain)NSMutableArray *attresArray;
@end

@implementation CKWaterFlowLayout

// 所有的懒加载
- (NSMutableDictionary *)maxYDict
{
    if (!_maxYDict) {
        self.maxYDict = [[NSMutableDictionary alloc]init];
    }
    return _maxYDict;
}

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

- (instancetype)init
{
    // 默认值是10 10 3 ，可以在控制器里面设置
    if (self = [super init]) {
        self.columnMargin = 10;
        self.rowMargin = 10;
        self.columnsCount = 3;
    }
    return self;
}

// 允许滑动
- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
    return YES;
}

// 每次布局前的准备
- (void)prepareLayout
{
    [super prepareLayout];
    for (int i = 0; i < self.columnsCount; i++) {
        NSString *column = [NSString stringWithFormat:@"%d",i];
        self.maxYDict[column] = @(self.sectionInset.top);
    }
    [self.attresArray removeAllObjects];
    NSInteger count = [self.collectionView numberOfItemsInSection:0];
    for (int i = 0; i < count; i++) {
        UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:i inSection:0]];
        [self.attresArray addObject:attrs];
    }
}


//  返回所有的尺寸
- (CGSize)collectionViewContentSize
{
    // 假装第0列最大
    __block NSString *maxColumn = @"0";
    [self.maxYDict enumerateKeysAndObjectsUsingBlock:^(NSString *column, NSNumber *maxY, BOOL * _Nonnull stop) {
        if ([maxY floatValue] > [self.maxYDict[maxColumn] floatValue]) {
            maxColumn = column;
        }
    }];
    return CGSizeMake(0,[self.maxYDict[maxColumn] floatValue]);
}


// 计算返回所有indexPath这个位置Item的布局属性
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    // 假装第0列最短
    __block NSString *minColumn = @"0";
    [self.maxYDict enumerateKeysAndObjectsUsingBlock:^(NSString *column, NSNumber *maxY, BOOL * _Nonnull 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;
    self.maxYDict[minColumn] = @(y + height);
    UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    attrs.frame = CGRectMake(x, y, width, height);
    return attrs;
}


- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
    return self.attresArray;
}

@end

————————————————————————回到顶部——————————————————————

 UIBarButtonItem *rightButtonItem = [[UIBarButtonItem alloc]initWithTitle:@"返回顶部" style:(UIBarButtonItemStylePlain) target:self action:@selector(rightButtonItemAction)];

    self.navigationItem.rightBarButtonItem = rightButtonItem;

- (void)rightButtonItemAction
{
    [self.collectionView setContentOffset:CGPointMake(0, -64) animated:YES];

}

点击状态栏返回顶部

self.collectionView.scrollsToTop = TRUE;

——————————————————————Label透明度字体跟着变浅的解决方法——————————————