A common use case for wanting to calculate the frame a label will take up is for sizing table view cells appropriately. The recommended way of doing this is using the NSString method boundingRectWithSize:options:attributes:context:.
options takes String drawing options:
NSStringDrawingUsesLineFragmentOrigin should be used for labels with multiple lines
NSStringDrawingTruncatesLastVisibleLine should be added using the | operator if there are a maximum number of lines
attributes is an NSDictionary of attributes that effect attributed strings (full list: Apple Docs) but the factors that effect height include:
context should be nil since the primary NSStringDrawingContext use case is for allowing font to resize to fit a specified rect, which shouldn’t be the case if we’re calculating a dynamic height.
Objective C
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
NSString *labelContent = cell.theLabel.text;
// you may choose to get the content directly from the data source if you have done minimal customizations to the font or are comfortable with hardcoding a few values
// NSString *labelContent = [self.dataSource objectAtIndexPath:indexPath];
// value may be hardcoded if retrieved from data source
NSFont *labelFont = [cell.theLabel font];
// The NSParagraphStyle, even if you did not code any changes these values may have been altered in IB
NSMutableParagraphStyle *paragraphStyle = [NSMutableParagraphStyle new];
paragraphStyle.lineBreakMode = NSLineBreakByWordWrapping;
paragraphStyle.alignment = NSTextAlignmentCenter;
NSDictionary *attributes = @{NSFontAttributeName: labelFont,
NSParagraphStyleAttributeName: paragraphStyle};
// The width is also important to the height
CGFloat labelWidth = CGRectGetWidth(cell.theLabel.frame);
// If you have been hardcoding up to this point you will be able to get this value by subtracting the padding on left and right from tableView.bounds.size.width
// CGFloat labelWidth = CGRectGetWidth(tableView.frame) - 20.0f - 20.0f;
CGRect bodyBounds = [labelContent boundingRectWithSize:CGSizeMake(width, CGFLOAT_MAX) options:NSStringDrawingUsesLineFragmentOrigin attributes:attributes context:nil];
return CGRectGetHeight(bodyBounds) + heightOfObjectsOnTopOfLabel + heightOfObjectBelowLabel;
}Swfit 3
override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
var cell = tableView.cellForRow(atIndexPath: indexPath)!
var labelContent = cell.theLabel.text
var labelFont = cell.theLabel.font
var paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineBreakMode = .byWordWrapping
paragraphStyle.alignment = .center
var attributes = [NSFontAttributeName: labelFont, NSParagraphStyleAttributeName: paragraphStyle]
var labelWidth: CGFloat = cell.theLabel.frame.width
var bodyBounds = labelContent.boundingRect(withSize: CGSize(width: width, height: CGFLOAT_MAX), options: .usesLineFragmentOrigin, attributes: attributes, context: nil)
return bodyBounds.height + heightOfObjectsOnTopOfLabel + heightOfObjectBelowLabel
}Conversely, if you do have a set maximum number of lines you will first need calculate the height of a single line to make sure we don’t get a value taller than the allowed size:
// We calculate the height of a line by omitting the NSStringDrawingUsesLineFragmentOrigin option, which will assume an infinitely wide label
CGRect singleLineRect = [labelContent boundingRectWithSize:CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX)
options:NSStringDrawingTruncatesLastVisibleLine
context:nil];
CGFloat lineHeight = CGRectGetHeight(singleLineRect);
CGFloat maxHeight = lineHeight * cell.theLabel.numberOfLines;
// Now you can call the method appropriately
CGRect bodyBounds = [labelContent boundingRectWithSize:CGSizeMake(width, maxHeight) options:(NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingTruncatesLastVisibleLine) attributes:attributes context:nil];
return CGRectGetHeight(bodyBounds) + heightOfObjectsOnTopOfLabel + heightOfObjectBelowLabel;