UITableView使用autolayout如何自适应高度

- (CGFloat) tableView: (UITableView *) tableView heightForRowAtIndexPath: (NSIndexPath *) indexPath
{
static TSTableViewCell *sizingCell;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{

sizingCell = (TSTableViewCell*)[tableView dequeueReusableCellWithIdentifier: @"TSTableViewCell"];
});

// configure the cell
sizingCell.text = self.cellText;

// force layout
[sizingCell setNeedsLayout];
[sizingCell layoutIfNeeded];

// get the fitting size
CGSize s = [sizingCell.contentView systemLayoutSizeFittingSize: UILayoutFittingCompressedSize];
NSLog( @"fittingSize: %@", NSStringFromCGSize( s ));

return s.height;
}