UILable怎么设置行高，然后多行之后怎么算高度

UIFont *font = [UIFont fontWithName:@"Helvetica" size:17.0];

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath //里面这样设置

cell.textLabel.lineBreakMode = NSLineBreakByWordWrapping;
cell.textLabel.numberOfLines = 0;
cell.textLabel.font =font;

UIFont *cellFont = [UIFont fontWithName:@"Helvetica" size:17.0];
CGSize constraintSize = CGSizeMake(280.0f, MAXFLOAT);
CGSize labelSize = [cell.textLabel.text sizeWithFont:cellFont constrainedToSize:constraintSize lineBreakMode:NSLineBreakByWordWrapping];

CGRect frame = cell.textLabel.frame;
cell.textLabel.frame = CGRectMake(frame.origin.x, ((labelSize.height + 20)-frame.size.height)/2, frame.size.width, frame.size.height);//设置高度

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{//返回计算高度
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NSString *cellText = item.name;
UIFont *cellFont = font
CGSize constraintSize = CGSizeMake(280.0f, MAXFLOAT);
CGSize labelSize = [cellText sizeWithFont:cellFont constrainedToSize:constraintSize lineBreakMode:NSLineBreakByWordWrapping];

return labelSize.height + 20;
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