textbox 글자수에 따른 height 가져오기

int nMaxWidth = 220; 

int nMaxHeight = 400;   

UIFont *chatFont = [UIFont systemFontOfSize:14];

_tagDetail.text = @"";

CGSize chatTextSize = [_tagDetail.text sizeWithFont:  chatFont

  constrainedToSize: CGSizeMake(nMaxWidth, nMaxHeight)

  lineBreakMode: UILineBreakModeWordWrap];

int height = chatTextSize.height;