iOS UICollectionView reloadData后找到某个cell 更新某个cell数据

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在开发中有个需求, 要在刷新完数据后再修改其中某些cell的属性, 结果发现是有问题的

    [self.collectionView reloadData];    UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:indexPath];    cell.backgroundColor = [UIColor redColor];

debug发现在执行完reloadData方法后并没有立即刷新cell, 而是执行了下面对cell操作的代码, 当这个方法执行完成后reloadData才会去刷新数据, 从而导致我们对cell的操作又被刷新的时候修改了

要解决这个问题 ,可以这么操作

    [self.collectionView reloadData];    NSMutableArray *indexPaths = [NSMutableArray array];    for (int i = 0; i < 10 ; i++) {        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:i inSection:0];        [indexPaths addObject:indexPath];    }    [self.collectionView performBatchUpdates:^{        [self.collectionView reloadItemsAtIndexPaths:indexPaths];    } completion:^(BOOL finished) {    for (NSIndexPath *indexPath in indexPaths) {        UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:indexPath];        cell.backgroundColor = [UIColor redColor];        }    }];

如果操作的cell未在现实区域,可以这么操作(此方法来源于网络)
可以先让 collection view 滚动到目标 cell 处，然后在打开 cell。这里需要用到 scroll 的代理方法，以在滚动动画结束的时候，找到目标 cell。（滚动结束才能确定目标 cell 是 visible 的。）你还需要定义一个 indexPath 值以区分滚动结束的时候是否需要打开cell，以及要打开哪个 cell。代码如下,

NSIndexPath *needOpenCellIndexPath;- (void)foo{    needOpenCellIndexPath = ...;    [self.collectionView performBatchUpdates:^{        [self.collectionView reloadItemsAtIndexPaths:@[needOpenCellIndexPath]];    } completion:^(BOOL finished) {        UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:needOpenCellIndexPath];        if (cell) {            [self performSegueWithIdentifier:RPAOpenMapSegueIdentifier sender:cell];        } else {            // Start scrolling to the target cell.            [self.collectionView selectItemAtIndexPath:needOpenCellIndexPath animated:YES scrollPosition:UICollectionViewScrollPositionTop];        }        }];}#pragma mark - scroll view deleagte- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView{    if (needOpenCellIndexPath) {        UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:needOpenCellIndexPath];        [self performSegueWithIdentifier:openInFileIdentifier sender:cell];    }    needOpenCellIndexPath = nil;}#pragma mark -

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