检查UITableViewCell是否完全可见的最佳方法

我有一个带有不同高度的单元格的UITableView，我需要知道它们何时完全可见。

现在，我遍历可见单元列表中的每个单元，以检查每次滚动视图时是否完全可见。这是最好的方法吗？

这是我的代码：

- (void)scrollViewDidScroll:(UIScrollView *)aScrollView {

    CGPoint offset = aScrollView.contentOffset;
    CGRect bounds = aScrollView.bounds;    
    NSArray* cells = myTableView.visibleCells;

    for (MyCustomUITableViewCell* cell in cells) {

        if (cell.frame.origin.y > offset.y &&
            cell.frame.origin.y + cell.frame.size.height < offset.y + bounds.size.height) {

            [cell notifyCompletelyVisible];
        }
        else {

            [cell notifyNotCompletelyVisible];
        }
    }
}

编辑：

请注意，*-（NSArray ）visibleCells返回的可见单元格既完全可见又部分可见。

编辑2：

这是结合了lnafziger和Vadim Yelagin的解决方案之后的修订代码：

- (void)scrollViewDidScroll:(UIScrollView *)aScrollView {
    NSArray* cells = myTableView.visibleCells;
    NSArray* indexPaths = myTableView.indexPathsForVisibleRows;

    NSUInteger cellCount = [cells count];

    if (cellCount == 0) return;

    // Check the visibility of the first cell
    [self checkVisibilityOfCell:[cells objectAtIndex:0] forIndexPath:[indexPaths objectAtIndex:0]];

    if (cellCount == 1) return;

    // Check the visibility of the last cell
    [self checkVisibilityOfCell:[cells lastObject] forIndexPath:[indexPaths lastObject]];

    if (cellCount == 2) return;

    // All of the rest of the cells are visible: Loop through the 2nd through n-1 cells
    for (NSUInteger i = 1; i < cellCount - 1; i++)
        [[cells objectAtIndex:i] notifyCellVisibleWithIsCompletelyVisible:YES];
}

- (void)checkVisibilityOfCell:(MultiQuestionTableViewCell *)cell forIndexPath:(NSIndexPath *)indexPath {
    CGRect cellRect = [myTableView rectForRowAtIndexPath:indexPath];
    cellRect = [myTableView convertRect:cellRect toView:myTableView.superview];
    BOOL completelyVisible = CGRectContainsRect(myTableView.frame, cellRect);

    [cell notifyCellVisibleWithIsCompletelyVisible:completelyVisible];
}

您可以使用rectForRowAtIndexPath:method 获取单元格的rect，并使用CGRectContainsRectfunction 将其与tableview的rect进行比较。

请注意，如果该单元格不可见，它将不会实例化该单元格，因此将相当快。

迅速

let cellRect = tableView.rectForRowAtIndexPath(indexPath)
let completelyVisible = tableView.bounds.contains(cellRect)

对象

CGRect cellRect = [tableView rectForRowAtIndexPath:indexPath];
BOOL completelyVisible = CGRectContainsRect(tableView.bounds, cellRect);

当然，这不会考虑到表视图被超级视图剪切或被另一个视图遮挡。

我会这样更改：

- (void)checkVisibilityOfCell:(MyCustomUITableViewCell *)cell inScrollView:(UIScrollView *)aScrollView {
    CGRect cellRect = [aScrollView convertRect:cell.frame toView:aScrollView.superview];

    if (CGRectContainsRect(aScrollView.frame, cellRect))
        [cell notifyCompletelyVisible];
    else
        [cell notifyNotCompletelyVisible];
}

- (void)scrollViewDidScroll:(UIScrollView *)aScrollView { 
    NSArray* cells = myTableView.visibleCells;

    NSUInteger cellCount = [cells count];
    if (cellCount == 0)
        return;

    // Check the visibility of the first cell
    [self checkVisibilityOfCell:[cells firstObject] inScrollView:aScrollView];
    if (cellCount == 1)
        return;

    // Check the visibility of the last cell
    [self checkVisibilityOfCell:[cells lastObject] inScrollView:aScrollView];
    if (cellCount == 2)
        return;

    // All of the rest of the cells are visible: Loop through the 2nd through n-1 cells
    for (NSUInteger i = 1; i < cellCount - 1; i++)
        [[cells objectAtIndex:i] notifyCompletelyVisible];
}

您可以尝试执行以下操作来查看可见的百分比：

-(void)scrollViewDidScroll:(UIScrollView *)sender
{
    [self checkWhichVideoToEnable];
}

-(void)checkWhichVideoToEnable
{
    for(UITableViewCell *cell in [tblMessages visibleCells])
    {
        if([cell isKindOfClass:[VideoMessageCell class]])
        {
            NSIndexPath *indexPath = [tblMessages indexPathForCell:cell];
            CGRect cellRect = [tblMessages rectForRowAtIndexPath:indexPath];
            UIView *superview = tblMessages.superview;

            CGRect convertedRect=[tblMessages convertRect:cellRect toView:superview];
            CGRect intersect = CGRectIntersection(tblMessages.frame, convertedRect);
            float visibleHeight = CGRectGetHeight(intersect);

            if(visibleHeight>VIDEO_CELL_SIZE*0.6) // only if 60% of the cell is visible
            {
                // unmute the video if we can see at least half of the cell
                [((VideoMessageCell*)cell) muteVideo:!btnMuteVideos.selected];
            }
            else
            {
                // mute the other video cells that are not visible
                [((VideoMessageCell*)cell) muteVideo:YES];
            }
        }
    }
}

从文档：

visibleCells返回在接收器中可见的表单元格。

- (NSArray *)visibleCells

返回值包含UITableViewCell对象的数组，每个对象代表接收表视图中的可见单元格。

可用性在iOS 2.0和更高版本中可用。

另请参见– indexPathsForVisibleRows

如果您还想将contentInset考虑在内，并且不想依赖于一个超级视图（超级视图中的表视图框架可能不是0,0的东西），这是我的解决方案：

extension UITableView {

    public var boundsWithoutInset: CGRect {
        var boundsWithoutInset = bounds
        boundsWithoutInset.origin.y += contentInset.top
        boundsWithoutInset.size.height -= contentInset.top + contentInset.bottom
        return boundsWithoutInset
    }

    public func isRowCompletelyVisible(at indexPath: IndexPath) -> Bool {
        let rect = rectForRow(at: indexPath)
        return boundsWithoutInset.contains(rect)
    }
}

- (BOOL)checkVisibilityOfCell{
    if (tableView.contentSize.height <= tableView.frame.size.height) {
        return YES;
    } else{
        return NO;
    }
}

UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:indexPath];
CGRect frame = cell.frame;
if (CGRectContainsRect(CGRectOffset(self.collectionView.frame, self.collectionView.contentOffset.x, self.collectionView.contentOffset.y), frame))
{
    // is on screen
}

即使您说每次滚动时都想检查它，也可以使用

-(void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
       CGRect cellRect = [tableView convertRect:cell.frame toView:tableView.superview];
       if (CGRectContainsRect(tableView.frame, cellRect)){
            //Do things in case cell is fully displayed
        }

}

也许对此问题更好地使用了UITableViewDelegate的next函数

func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath)

下面的代码可让您检查集合视图单元格是否通过集合视图的布局属性完全可见。

guard let cellRect = collectionView.layoutAttributesForItem(at: indexPath)?.frame else { return } let isCellCompletelyVisible = collectionView.bounds.contains(cellRect)