UICollectionView cellForItemAtIndexPath 为 nil [英] UICollectionView cellForItemAtIndexPath is nil

问题描述

我有一个更新现有 UICollectionView 的函数.UICollectionView 已创建，我可以看到它，但是当我想访问它的单元格来更新它时，它们是 nil.

I have a function that updates existing UICollectionView. The UICollectionView is created, I can see it, but when I want to access its cells to update it, they are nil.

-(void)finishExam{

    for (int i = 0; i < [self.questionsOverviewCollection numberOfItemsInSection:0]; i++) {

        NSLog(@"self.questionsOverviewCollection - %@",self.questionsOverviewCollection);
        NSLog(@"cell - %@",[self.questionsOverviewCollection cellForItemAtIndexPath:[NSIndexPath indexPathForRow:i inSection:0]]);
        NSLog(@"overviewCell - %@",(OverviewCell*)[self.questionsOverviewCollection cellForItemAtIndexPath:[NSIndexPath indexPathForRow:i inSection:0]]);
        NSLog(@"numOfCells - %d", [self.questionsOverviewCollection numberOfItemsInSection:0]);

        OverviewCell *cell = (OverviewCell*)[self.questionsOverviewCollection cellForItemAtIndexPath:[NSIndexPath indexPathForRow:i inSection:0]];
            [cell finishExam];
    }
}


- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{

    OverviewCell *cell = (OverviewCell*)[collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];

    [cell someSetUp];

    return cell;
}

日志:

self.questionsOverviewCollection - <UICollectionView: 0xa1abc00; frame = (14 219; 217 441); clipsToBounds = YES; opaque = NO; autoresize = W+H; gestureRecognizers = <NSArray: 0xe0617a0>; layer = <CALayer: 0xe0bbb00>; contentOffset: {0, 0}> collection view layout: <UICollectionViewFlowLayout: 0xe0cc3f0>
cell - (null)
overviewCell - (null)
numOfCells - 30

推荐答案

来自 UICollectionView 文档(强调我自己的)

From the UICollectionView docs (emphasis my own)

返回值
对应索引路径处的单元格对象；如果单元格不可见，则为 nil 或 indexPath 超出范围.

Return Value
The cell object at the corresponding index path or nil if the cell is not visible or indexPath is out of range.

你应该更新你的底层模型，它为视图提供数据.

You should update your underlying model, which provides the data to the views.

这篇关于UICollectionView cellForItemAtIndexPath 为 nil的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！