不知道写了多少次collectionview，步了很多坑，现在看来虽然达到了自己想要的结果，却不知道其中所以然。还是总结一下，免得再走弯路；
场景是这样的，我要定制一个显示选择图片的排列，想要实现横向排列4个，等间距，多了折行显示的效果，正确的做法是这样的；
- (void)viewDidLoad {
[super viewDidLoad];
self.navigationController.navigationBar.translucent = NO;
if ([self respondsToSelector:@selector(setAutomaticallyAdjustsScrollViewInsets:)]) {
self.automaticallyAdjustsScrollViewInsets = NO;
}
self.view.backgroundColor = [UIColor purpleColor];
self.photoArray = @[[UIImage imageNamed:@"cycle3"],[UIImage imageNamed:@"cycle4"],[UIImage imageNamed:@"cycle2"],[UIImage imageNamed:@"cycle3"],[UIImage imageNamed:@"cycle4"],].mutableCopy;
[self.view addSubview:self.pickPhotoCollection];
}
-(UICollectionView *)pickPhotoCollection{
if (!_pickPhotoCollection) {
UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc]init];
layout.scrollDirection = UICollectionViewScrollDirectionVertical;
_pickPhotoCollection = [[UICollectionView alloc]initWithFrame:CGRectMake(, , kScreenWidth, (self.photoArray.count/ +)*) collectionViewLayout:layout];
_pickPhotoCollection.delegate = self;
_pickPhotoCollection.dataSource = self;
_pickPhotoCollection.backgroundColor = RGBACOLOR(, , , );
_pickPhotoCollection.showsHorizontalScrollIndicator = NO;
[_pickPhotoCollection registerClass:[XJPickPhotoCollectionViewCell class] forCellWithReuseIdentifier:NSStringFromClass([XJPickPhotoCollectionViewCell class])];
}
return _pickPhotoCollection;
}
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{
return ;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
return self.photoArray.count + > ? : self.photoArray.count +;
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
XJPickPhotoCollectionViewCell *cell = (XJPickPhotoCollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:NSStringFromClass([XJPickPhotoCollectionViewCell class]) forIndexPath:indexPath];
//判断图片的显示方式 如果不是9张图 则显示可以继续添加
if (self.photoArray.count == ) {
cell.photoImageView.image = self.photoArray[indexPath.row];
return cell;
}
if (indexPath.row == self.photoArray.count) {
cell.photoImageView.image = [UIImage imageNamed:@"addPhoto"];
}else{
cell.photoImageView.image = self.photoArray[indexPath.row];
}
return cell;
}
-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath{
return CGSizeMake(WidthScale(), WidthScale());
}
-(CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section{
// return 2;
return (kScreen_width - WidthScale()* - )/.;
}
//-(CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section{
// return (kScreen_width - WidthScale(70)*4 - 10 )/3.;
//}
-(UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section{
return UIEdgeInsetsMake(, , , );
}
关键点在这里：
1-===layout.scrolldirection = uicollectionViewScrollDirectionVertical;collection的滚动方向，由于要折行向下，所以方向是垂直方向，在排列的时候会默认选择先将横向排列完毕，折行向下。
2--=== minmumlinespaceing 这个这个属性用来指示行与行之间的最小距离(纵向)，或者列与列之间的最小距离(横向)。无论横向或者纵向，都可以滚动显示所有内容，所以这个属性可以单独设置。 SO 在不同的滚动方向上要分清楚他的作用，我就是在这里弄的头晕目眩； 当然interitem就很好理解了
另外还有一点是 如果是自定义的layout，layout的代理方法是不会执行的，若想达到相同的效果，需要在自定义的layout内部进行处理！
layout.scrollDirection = UICollectionViewScrollDirectionVertical;