1.UICollectionView参数的理解

```javascript

// line   跟滚动方向相同的间距

flowLay.minimumLineSpacing = 10;

 // item  跟滚动方向垂直的间距

flowLay.minimumInteritemSpacing = 10;

-(UICollectionView *)userImageCollectionView

{

if (_userImageCollectionView == nil) {

UICollectionViewFlowLayout *flowLay = [[UICollectionViewFlowLayout alloc]init];

//每个cell的大小 40 60

flowLay.itemSize = CGSizeMake(CGRectGetHeight(_tripCollectionView.frame) - 10 - 20 , CGRectGetHeight(_tripCollectionView.frame) - 10);

//每个section距collectionView的边界或者section上左下右的苦力

flowLay.sectionInset = UIEdgeInsetsMake(5, 10, 5, 10);

//cell之间的最小距离

flowLay.minimumInteritemSpacing = 10;

//每行cell之间的最小距离

flowLay.minimumLineSpacing = 10;

flowLay.scrollDirection = UICollectionViewScrollDirectionVertical;

_userImageCollectionView = [[UICollectionView alloc]initWithFrame:(CGRectMake(CGRectGetMinX(_tripCollectionView.frame), CGRectGetMaxY(_tripCollectionView.frame), CGRectGetWidth(_tripCollectionView.frame), CGRectGetHeight(_tripCollectionView.frame) * 2)) collectionViewLayout:flowLay];

_userImageCollectionView.layer.cornerRadius = 5;

_userImageCollectionView.layer.masksToBounds = YES;

_userImageCollectionView.bounces = NO;

_userImageCollectionView.backgroundColor = [[UIColor blackColor]colorWithAlphaComponent:0.5];;

[self.mapView addSubview:_userImageCollectionView];

_userImageCollectionView.hidden = YES;

}

return _userImageCollectionView;

}

```