iOS UICollectionView实现标签选择器

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。

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