UICollectionView实现的标签选择器

近来，在项目中需要实现一个类似兴趣标签的选择器。由于标签的文字长度不定，所以标签的显示长度就不定。为了实现效果，就使用了UICollectionView来实现了每行的标签数量不定、cell的宽度自适应的效果。先在此分享出来：

1、自适应UICollectionViewCell

这里只是在自适应UICollectionViewCell上放一个和UICollectionViewCell保持一样大小的按钮，当选中和取消选中时改变按钮的文字颜色和边框颜色：

#pragma mark---标签cell@implementation YLTagsCollectionViewCell-(instancetype)initWithFrame:(CGRect)frame{    if(self = [super initWithFrame:frame]){        self.backgroundColor = [UIColor clearColor];        _btn = [UIButton buttonWithType:UIButtonTypeCustom];        //此处可以根据需要自己使用自动布局代码实现        _btn.frame = CGRectMake(0, 0, frame.size.width, frame.size.height);        _btn.backgroundColor = [UIColor whiteColor];        _btn.titleLabel.font = [UIFont systemFontOfSize:14];        _btn.layer.borderWidth = 1.f;        _btn.layer.cornerRadius = frame.size.height/2.0;        _btn.layer.masksToBounds = YES;        [_btn setTitleColor:HEXCOLOR(0x666666) forState:UIControlStateNormal];        _btn.layer.borderColor = HEXCOLOR(0xdddddd).CGColor;        _btn.userInteractionEnabled = NO;        [self.contentView addSubview:_btn];    }    return self;}-(void)layoutSubviews{    [super layoutSubviews];    _btn.frame = CGRectMake(0, 0, self.contentView.frame.size.width, self.contentView.frame.size.height);}-(void)setSelected:(BOOL)selected{    [super setSelected:selected];    _btn.layer.borderColor = selected?HEXCOLOR(0xffb400).CGColor:HEXCOLOR(0xdddddd).CGColor;    [_btn setTitleColor:selected?HEXCOLOR(0xffb400):HEXCOLOR(0x666666) forState:UIControlStateNormal];}-(void)setHighlighted:(BOOL)highlighted{    [super setHighlighted:highlighted];    _btn.layer.borderColor = highlighted?HEXCOLOR(0xffb400).CGColor:HEXCOLOR(0xdddddd).CGColor;    [_btn setTitleColor:highlighted?HEXCOLOR(0xffb400):HEXCOLOR(0x666666) forState:UIControlStateNormal];}@end

2、UICollectionViewFlowLayout子类--YLWaterFlowLayout的实现

.h头文件

#import <UIKit/UIKit.h>@class YLWaterFlowLayout;@protocol  YLWaterFlowLayoutDelegate <NSObject>/**通过代理获得每个cell的宽度*/- (CGFloat)waterFlowLayout:(YLWaterFlowLayout *)layout widthAtIndexPath:(NSIndexPath *)indexPath;@end@interface YLWaterFlowLayout : UICollectionViewFlowLayout@property (nonatomic,assign) id<YLWaterFlowLayoutDelegate> delegate;@property(nonatomic,assign)CGFloat rowHeight;///< 固定行高@end

.m文件

#import "YLWaterFlowLayout.h"@interface YLWaterFlowLayout()@property(nonatomic,strong)NSMutableArray *originxArray;@property(nonatomic,strong)NSMutableArray *originyArray;@end@implementation YLWaterFlowLayout#pragma mark - 初始化属性- (instancetype)init {    self = [super init];    if (self) {        self.minimumInteritemSpacing = 5;//同一行不同cell间距        self.minimumLineSpacing = 5;//行间距        self.sectionInset = UIEdgeInsetsMake(10, 10, 10, 10);        self.scrollDirection = UICollectionViewScrollDirectionVertical;        _originxArray = [NSMutableArray array];        _originyArray = [NSMutableArray array];    }    return self;}#pragma mark - 重写父类的方法，实现瀑布流布局#pragma mark - 当尺寸有所变化时，重新刷新- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {    return YES;}- (void)prepareLayout {    [super prepareLayout];}#pragma mark - 处理所有的Item的layoutAttributes- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{    NSArray *array = [super layoutAttributesForElementsInRect:rect];    NSMutableArray *mutArray = [NSMutableArray arrayWithCapacity:array.count];    for(UICollectionViewLayoutAttributes *attrs in array){        UICollectionViewLayoutAttributes *theAttrs = [self layoutAttributesForItemAtIndexPath:attrs.indexPath];        [mutArray addObject:theAttrs];    }    return mutArray;}#pragma mark - 处理单个的Item的layoutAttributes- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{    CGFloat x = self.sectionInset.left;    CGFloat y = self.sectionInset.top;    //判断获得前一个cell的x和y    NSInteger preRow = indexPath.row - 1;    if(preRow >= 0){        if(_originyArray.count > preRow){            x = [_originxArray[preRow]floatValue];            y = [_originyArray[preRow]floatValue];        }        NSIndexPath *preIndexPath = [NSIndexPath indexPathForItem:preRow inSection:indexPath.section];        CGFloat preWidth = [self.delegate waterFlowLayout:self widthAtIndexPath:preIndexPath];        x += preWidth + self.minimumInteritemSpacing;    }    CGFloat currentWidth = [self.delegate waterFlowLayout:self widthAtIndexPath:indexPath];    //保证一个cell不超过最大宽度    currentWidth = MIN(currentWidth, self.collectionView.frame.size.width - self.sectionInset.left - self.sectionInset.right);    if(x + currentWidth > self.collectionView.frame.size.width - self.sectionInset.right){        //超出范围，换行        x = self.sectionInset.left;        y += _rowHeight + self.minimumLineSpacing;    }    // 创建属性    UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];    attrs.frame = CGRectMake(x, y, currentWidth, _rowHeight);    _originxArray[indexPath.row] = @(x);    _originyArray[indexPath.row] = @(y);    return attrs;}#pragma mark - CollectionView的滚动范围- (CGSize)collectionViewContentSize{    CGFloat width = self.collectionView.frame.size.width;    __block CGFloat maxY = 0;    [_originyArray enumerateObjectsUsingBlock:^(NSNumber *number, NSUInteger idx, BOOL * _Nonnull stop) {        if ([number floatValue] > maxY) {            maxY = [number floatValue];        }    }];    return CGSizeMake(width, maxY + _rowHeight + self.sectionInset.bottom);}@end

实现思路：在YLWaterFlowLayout中使用originxArray和originyArray两个个数组记录了每一个自定义YLTagsCollectionViewCell的位置x和y。

在 -(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath方法中通获得与当前YLTagsCollectionViewCell临近的“上一个YLTagsCollectionViewCell”的位置和尺寸信息，将上一个cell的x加上上一个cell的width来得到当前cell的x。同时还要判断当前cell的x+width是否会超越出屏幕右边缘，如果超出，则表明需要换行显示了，这时候就要修改y的值了。

3、效果图