Why do UITableView zero height cells leave space gaps? - ios

Question

My Objective-C Catalyst application has a table view which displays hierarchical data in the form of Groups within Groups and Notes and Groups within Groups. The Groups have a disclosure control that when toggled either "opens" the group to display its contents, or "closes" the group to hide its contents.
The problem, as illustrated by the following two screenshots, is that when a Group containing more than a few items is "closed", a noticeable vertical gap space is shown below the "closed" group. The height of the gap space is proportional to the number of items within the "closed" group. When the "closed" group is toggled "open", the gap space disappears––returns to normal cell spacing. This problem exists in both the iOS and macOS builds of the Catalyst app.
The tableView cells are Style Custom cells. The display of "open" or "closed" groups is controlled by varying the cell height based on whether an item is visible or not. If an item is buried within a "closed" Group, the cell's height is set to zero, otherwise the cell's height is set normally. This is accomplished in the tableView delegate - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath:
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
…
…
…
// Node is hidden if an ancestor is collapsed.
if ([model isNodeWithinCollapsedAncestor:node]) {
return 0;
} else {
return [super tableView:tableView heightForRowAtIndexPath:indexPath];
}
}
I have tried numerous modifications in attempt to eliminate these gaps, without success. Among these are:
Varied UITableView attributes.
Varied UITableViewCell attributes.
Set cell.contentView.layoutMargins.
Set cell.contentView.hidden = YES (even worse gaps since it leaves whitespace for every hidden cell).
Varied cell constraints.
Replaced Style Custom cells with Style Basic cells. (Since Basic cells still had gaps, I believe it rules out my Custom cells as the problem.)
Nothing seems to prevent the gap spaces. It appears to me that there is some residual height to a zero height cell, perhaps as little as a few points, but I have had no success in getting rid of the space gaps.