UICollectionView其实在开发中是比较常用，说简单也简单，网上的各种UICollectionView的博客一看，基本上就入门了，但是如果做项目经常会有种UICollectionView怎么这么坑的感觉，前面写过一篇关于UICollectionView自适应的博客UITableView和UICollecionView自适应，有兴趣的可以看一下,本文主要是UICollectionView的单元格是宽高相同设置最大间距和可变单元格的间距设置:

宽高相同设置最大间距

初始化数据:

   UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
   layout.itemSize = CGSizeMake(100, 40);
   layout.minimumInteritemSpacing=0;
   layout.sectionInset=UIEdgeInsetsMake(0, 0, 0, 0);
   [self.collectionView registerClass:[BookCollectionViewCell class] forCellWithReuseIdentifier:CollectionViewIdentifier];
   self.collectionView.backgroundColor      = [UIColor redColor];
   self.collectionView.collectionViewLayout = layout;
   self.data                                = [NSMutableArray array];
   
   [self.data addObject:@"北京"];
   [self.data addObject:@"FlyElephant"];
   [self.data addObject:@"编程"];
   [self.data addObject:@"加班"];
   [self.data addObject:@"Objective-C"];
   [self.data addObject:@"iOS"];
   [self.data addObject:@"UICollectioView自适应"];
}

UICollectionViewDataSource:

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
   return 1;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
   return [self.data count];
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
   BookCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CollectionViewIdentifier forIndexPath:indexPath];
   cell.contentLabel.text = self.data[indexPath.row];
   return cell;
}

上面是一个最普通的UICollectionView的布局，我们已经设置最小间距是0和边距，事实上间距是iOS帮我们计算出来布局的，如果我们想设置相邻的单元为我们想要的间距就需要设置最大间距，效果如下:

这时候需要自定义UICollectionViewFlowLayout，重写layoutAttributesForElementsInRect方法:

-(NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect{
   NSMutableArray *attributes = [[super layoutAttributesForElementsInRect:rect] mutableCopy];

   //注意起始值
   for(NSInteger i = 1; i < [attributes count]; i++){

       UICollectionViewLayoutAttributes *currentLayoutAttributes = attributes[i];
       
       UICollectionViewLayoutAttributes *prevLayoutAttributes = attributes[i - 1];
       
       NSInteger origin = CGRectGetMaxX(prevLayoutAttributes.frame);
   
       if(origin + ITEM_SPACING + currentLayoutAttributes.frame.size.width < self.collectionViewContentSize.width){
           CGRect frame = currentLayoutAttributes.frame;
           frame.origin.x = origin + ITEM_SPACING;
           currentLayoutAttributes.frame = frame;
       }
   }

   return attributes;
}

可变单元格设置最大间距

这里主要设置了预估大小，如果不太清楚，可以参考开头的文章链接，参考代码:

   FECollectionViewFlowLayout *layout = [[FECollectionViewFlowLayout alloc] init];
   layout.estimatedItemSize = CGSizeMake(100, 40);
   
   layout.minimumInteritemSpacing=0;
   layout.sectionInset=UIEdgeInsetsMake(0, 0, 0, 0);
   [self.collectionView registerClass:[BookCollectionViewCell class] forCellWithReuseIdentifier:CollectionViewIdentifier];
   self.collectionView.backgroundColor      = [UIColor redColor];
   self.collectionView.collectionViewLayout = layout;
   self.data                                = [NSMutableArray array];
   
   [self.data addObject:@"北京"];
   [self.data addObject:@"FlyElephant"];
   [self.data addObject:@"编程"];
   [self.data addObject:@"加班"];
   [self.data addObject:@"Objective-C"];
   [self.data addObject:@"iOS"];
   [self.data addObject:@"UICollectioView自适应"];

这里面有个坑就是如果按照上面的方式去设置最大间距，你会发现是没有任何效果的，这个坑才进去花了两个小时爬出来，解决方案很简单，自定义FECollectionViewFlowLayout重写layoutAttributesForItemAtIndexPath方法:

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
   UICollectionViewLayoutAttributes *layoutAttribute = [super layoutAttributesForItemAtIndexPath:indexPath];
   if (layoutAttribute.frame.origin.x == self.sectionInset.left) {
       return layoutAttribute;
   }
   
   NSIndexPath *previousIndexPath = [NSIndexPath indexPathForRow:indexPath.row-1 inSection:indexPath.section];
   UICollectionViewLayoutAttributes *previousLayoutAttribute = [self layoutAttributesForItemAtIndexPath:previousIndexPath];
   CGRect frame = layoutAttribute.frame;
   frame.origin.x        = CGRectGetMaxX(previousLayoutAttribute.frame)+0;
   layoutAttribute.frame = frame;
   return layoutAttribute;
}

代码地址：

GitHub:FlyElephant的GitHub，