iOSCollectioView滾動到指定section的方法

標籤：index   pos   ref   指定   組成   com   set   body   ott   

項目中的需求：collectionView頂部有一個scrollView組成的標籤，點擊標籤，讓collectionView滾動到指定的行，滾動collectionView自動切換到頂部指定的標籤

實現方法如下：

1. 保證collectionView全部載入完畢，我這裡通過一個bool的標誌位來標示

  -(void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath  {        if([indexPath row] == ((NSIndexPath*)[[collectionView indexPathsForVisibleItems] lastObject]).row){            self.isLoaded = YES;        }   }

2. 標籤點擊了CollectionView滾動到指定行

        if (self.isLoaded) {                        // scroll to selected index            NSIndexPath* cellIndexPath = [NSIndexPath indexPathForItem:0 inSection:index+1];            UICollectionViewLayoutAttributes* attr = [self.collectionView.collectionViewLayout layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:cellIndexPath];            UIEdgeInsets insets = self.collectionView.scrollIndicatorInsets;                        CGRect rect = attr.frame;            rect.size = self.collectionView.frame.size;            rect.size.height -= insets.top + insets.bottom;            CGFloat offset = (rect.origin.y + rect.size.height) - self.collectionView.contentSize.height;            if ( offset > 0.0 ) rect = CGRectOffset(rect, 0, -offset);                        [weakSelf.collectionView scrollRectToVisible:rect animated:YES];        }

3. CollectionView滾動到指定行的時候，同時切換標籤滾動

    -(void)scrollViewDidScroll:(UIScrollView *)scrollView{        static NSInteger currentIndex = 0;        NSInteger index=scrollView.contentOffset.y;        CGRect visibleRect = (CGRect){.origin = self.collectionView.contentOffset, .size = self.collectionView.bounds.size};        CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));        NSIndexPath *visibleIndexPath = [self.collectionView indexPathForItemAtPoint:visiblePoint];//        NSLog(@"%@",visibleIndexPath);        if (currentIndex == visibleIndexPath.section || visibleIndexPath == nil) {            return;        }        currentIndex = visibleIndexPath.section;       [self.itemTool itemScrollToPositionWithIndex:currentIndex isJump:YES];    }

iOSCollectioView滾動到指定section的方法