UICollectionView布局4个参数的理解

-(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上左下右的距离

        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;

}

    [_bgImageV mas_makeConstraints:^(MASConstraintMaker *make) {

        make.edges.equalTo(weakSelf).with.insets(UIEdgeInsetsZero);

//        make.top.left.bottom.and.right.equalTo(weakSelf).with.insets(UIEdgeInsetsZero);

    }];