UICollectionReusableView:行头行尾

前言:以前用UICollectionView一行的时候,行头行尾不会出现任何问题
当出现多行的时候,行头行尾的复用机制就开始坑爹了
注册

注册行头
[self.collectView registerNib:[UINib nibWithNibName:@"NibName" bundle:nil] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"ReuseIdentifier"];
或者
   [self.collectView registerClass:[Class class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"ReuseIdentifier"]; 

复用机制

-(UICollectionReusableView *) collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
    UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
    return headerView;
}

多行复用:于是苹果爸爸开始坑爹儿子(苹果:老子没你那么弱的儿子)

一、Class

 [self.collectView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView"]; 

        UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
        UIView *view = [[UIView alloc]initWithFrame:CGRectMake(0, 0, kScreenWidth, 45)];
        [headerView addSubview:view];

        NSString *text = (indexPath.section==0&&_model.theme_book_ids.count>0)?@"主题书籍":@"任务";
        UILabel *lb = [[UILabel alloc]initWithFrame:CGRectMake(16, 25, 300, 20)];
        [lb setText:text textColor:[UIColor colorWithHexString:@"#303133"] fontSize:19];
        [view addSubview:lb];

        return headerView;

1588663205403.jpg

二、nib

 [self.collectView registerNib:[UINib nibWithNibName:@"LFThemeReadBooksHeader" bundle:nil] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView"];

        LFThemeReadBooksHeader *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
        headerView.frame = CGRectMake(0, 0, kScreenWidth, 45);
        headerView.label.text = (indexPath.section==0&&_model.theme_book_ids.count>0)?@"主题书籍":@"任务";
return headerView;

1588662923064.jpg 1eac4dc6d3bd5acd5c9f20443f89a3bd.jpg.gif 1588663205403.jpg

解决方法:
一、Class
每次都清空之前的子控件,再加一遍 [headerView removeAllSubviews];

        UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
        [headerView removeAllSubviews];
        
        UIView *view = [[UIView alloc]initWithFrame:CGRectMake(0, 0, kScreenWidth, 45)];
        [headerView addSubview:view];
        
        NSString *text = (indexPath.section==0&&_model.theme_book_ids.count>0)?@"主题书籍":@"任务";
        UILabel *lb = [[UILabel alloc]initWithFrame:CGRectMake(16, 25, 300, 20)];
        [lb setText:text textColor:[UIColor colorWithHexString:@"#303133"] fontSize:19];
        [view addSubview:lb];

        return headerView;

二、nib
注册两个nib 分别调用

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        if (indexPath.section == 0) {
            Type1HeaderView *type1HeaderView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:Type1HeaderID forIndexPath:indexPath];
            return type1HeaderView;
        } else {
            Type2HeaderView *type2HeaderView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:Type2HeaderID forIndexPath:indexPath];
            return type2HeaderView;
        }
    }
    return nil;
}

三、重写initwithframe方法

-(instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor colorWithRed:230 / 255.0 green:230 / 255.0 blue:230 / 255.0 alpha:1.0];
        _titleLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, M_SIZE.width, M_SIZE.height / 14)];
        _titleLabel.textAlignment = NSTextAlignmentCenter;
        [self addSubview:_titleLabel];
    }
    return self;
}

爸爸已经告诉你了,是你个傻儿子不认真看

1588663205403.jpg

总结:
你可以把

• (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
  理解成
  -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
  唯一不同的是UICollectionReusableView的复用机制比UITableViewCell的更蛋疼(比如用nib的时候)