tiritea tiritea - 3 months ago 26
iOS Question

Autolayout ignores multi-line detailTextLabel when calculating UITableViewCell height (all styles)

So I'm trying to use the built-in UITableViewCell styles - specifically UITableViewCellStyleSubtitle - with a (single) line textLabel but multiline detailTextLabel. But the (auto) calculated cell height is consistently too short, and appears to ignore that there is more than 1 line of detail.

I've tried using numberOfLines=0, estimatedRowHeight, UITableViewAutomaticDimension, preferredMaxWidthLayout, etc, but in all the permutations the behavior - indeed for all the UITableViewCell styles - is it appears the UITableViewAutomaticDimension cell height calculation will correctly account for a multiline textLabel (yay!), but incorrectly assumes the detailTextlabel is at most single line (nay!). Consequently, cells with a multiline detailTextLabel are too short, and hence the cell content spills over the top and bottom of the cell.

enter image description here

I've posted a quick test app showing this behavior on GitHub here. Adding additional lines of text is fine - all the cell styles appropriately increase in height to accommodate - but adding additional lines of detail does nothing to change the cell height, and quickly causes the content to spill over; the text+detail are themselves laid out correctly, and together centered correctly over the middle of the cell (so in that sense layoutSubviews is working correctly), but the overall cell height itself is unchanged.

It almost seems like there are no actual top & bottom constraints between the cell.contentView and the labels, and instead the cell height is being calculated directly from the height of the (possibly multi-line) textLabel and (only single-line) detailTextLabel, and then everything is centered over the middle of the cell... Again, multiline textLabel is fine, and I'm doing nothing different between the textLabel and detailTextLabel, but only the former (correctly) adjusts the cell height.

So my question is, if it is possible to use the built-in UITableViewCell styles to reliably display multiline detailTextLabels, or is it simply not possible and you need to create a custom subclass instead? [or, almost equivalently, without having to override layoutSubviews in a subclass and rewire all the constraints manually].




[4 May 2016] Conclusion: as of iOS9 multi-line detailTextLabels dont work as expected with UITableViewAutomaticDimension; the cell will be consistently too short and the text/detail will spill over the top and bottom. Either you must manually compute the correct cell height yourself, or create and layout your own equivalent custom UITableViewCell subclass, or (see my answer below) subclass UITableViewCell and fix
systemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority:
to return the correct height [recommended]

Answer

Further investigations (see UITableViewCellTest) indicate that when UITableViewAutomaticDimension is enabled the system calls -systemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority: to calculate the cell height, and that this pretty much ignores the height of the detailTextLabel in its computation (bug !?). As a result, for UITableViewCellStyleSubtitle the cell height is always going to be too short [a single-line detailTextLabel may not quite spill over the cell, but that's only because of the existing top and bottom margins], and for UITableViewCellStyleValue1 or UITableViewCellStyleValue2 the height will be too short whenever the detailTextLabel is taller (eg more lines) than the textLabel. This is all a moot point for UITableViewCellStyleDefault which has no detailTextLabel.

My solution was to subclass and fix with:

- (CGSize)systemLayoutSizeFittingSize:(CGSize)targetSize
        withHorizontalFittingPriority:(UILayoutPriority)horizontalFittingPriority
              verticalFittingPriority:(UILayoutPriority)verticalFittingPriority
{
    CGSize size = [super systemLayoutSizeFittingSize:targetSize
                       withHorizontalFittingPriority:horizontalFittingPriority
                             verticalFittingPriority:verticalFittingPriority];
    CGFloat detailHeight = CGRectGetHeight(self.detailTextLabel.frame);
    if (detailHeight) { // if no detailTextLabel (eg style = Default) then no adjustment necessary
        // Determine UITableViewCellStyle by looking at textLabel vs detailTextLabel layout
        if (CGRectGetMinX(self.detailTextLabel.frame) > CGRectGetMinX(self.textLabel.frame)) { // style = Value1 or Value2
            CGFloat textHeight = CGRectGetHeight(self.textLabel.frame);
            // If detailTextLabel taller than textLabel then add difference to cell height
            if (detailHeight > textHeight) size.height += detailHeight - textHeight;
        } else { // style = Subtitle, so always add subtitle height
            size.height += detailHeight;
        }
    }
}

You can pull the full subclass from here: MultilineTableViewCell

So far this fix appears to work well, and has let me successfully use the built-in UITableViewCellStyles with multiline text and details, in self-sizing cells with dynamic type support. This avoids the trouble (and mess) of manually computing the desired cell heights in tableView:heightForRowAtIndexPath:, or having to create custom cell layouts.

Comments