CollectionView-布局之间的切换(水平和圆形,点击

1. 我们就进行设定,当点击屏幕的时候,进行布局的切换.

  -  (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
// 根据布局类型进行切换(如果是圆形布局)
if ([self.collectionView.collectionViewLayout isKindOfClass:[LXLCircleLayout class]]) {
// 设置布局为流水布局
 LXLFlowLayout *flow = [[LXLFlowLayout alloc]init];
 [self.collectionView setCollectionViewLayout:flow animated:YES];
    }else{
// 如果不是圆形布局,就设置成圆形布局
 [self.collectionView setCollectionViewLayout:self.circleLayout animated:YES];
    }
}

2. 我们发觉,我们确实能做到相互的切换,但是如果再次切换回圆形布局时,发现程序直接就处于崩溃了. 因为如果切换回去的话可能由于cell 数目的不确定性,或者重新切换的原因,造成布局再次出现错误,而无法正常显示. 我们通过查找,找到对应方法进行重写.(其中原因,我也不是很明白).

  - (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
  return YES;
}
  - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    
    NSMutableArray *layoutAtts = [NSMutableArray array];
    
     NSInteger count =  [self.collectionView numberOfItemsInSection:0];

   
    for (int i = 0; i < count ; i ++) {
        
        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:i inSection:0];
        
// 调用方法,直接返回对应索引的布局
        UICollectionViewLayoutAttributes *layoutAtt = [self layoutAttributesForItemAtIndexPath:indexPath];
       
// 如果返现只有一个 cell 的时候让你直接设置到中心点(相当于将以前的布局覆盖掉) 
        if (count == 1) {
            layoutAtt.center = CGPointMake(self.collectionView.frame.size.width * 0.5, self.collectionView.frame.size.height * 0.5);
        }
        
        
        [layoutAtts addObject:layoutAtt];
    }

    return layoutAtts;

}
// 对应索引的布局.(不会主动调用)
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSInteger count =  [self.collectionView numberOfItemsInSection:0];
    CGFloat WH = 50;
    CGFloat centerX = self.collectionView.frame.size.width * 0.5;
    CGFloat centerY = self.collectionView.frame.size.height * 0.5;
    CGFloat randius = centerY- 30;
    CGFloat angelMargin = M_PI * 2 / count;
 UICollectionViewLayoutAttributes *layoutAtt = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
        CGFloat a = sin(indexPath.row * angelMargin) * randius;
        CGFloat b = cos(indexPath.row * angelMargin) * randius;
         layoutAtt.center = CGPointMake(centerX + a, b+ centerY);
        layoutAtt.size = CGSizeMake(WH, WH);
         return layoutAtt;

}

3.点击 cell 去掉对应的 cell, 并且重新布局

- (void)collectionView:(nonnull UICollectionView *)collectionView didSelectItemAtIndexPath:(nonnull NSIndexPath *)indexPath
{
    [self.images removeObjectAtIndex:indexPath.row];
    [self.collectionView reloadData];
}