准确计算CoreText高度的方法：

- (int)getAttributedStringHeightWithString:(NSAttributedString *)  string  WidthValue:(int) width

{

   int total_height = ;

   CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)string);    //string 为要计算高度的NSAttributedString

   CGRect drawingRect = CGRectMake(, , width, );  //这里的高要设置足够大

   CGMutablePathRef path = CGPathCreateMutable();

   CGPathAddRect(path, NULL, drawingRect);

   CTFrameRef textFrame = CTFramesetterCreateFrame(framesetter,CFRangeMake(,), path, NULL);

   CGPathRelease(path);

   CFRelease(framesetter);

   NSArray *linesArray = (NSArray *) CTFrameGetLines(textFrame);

   CGPoint origins[[linesArray count]];

   CTFrameGetLineOrigins(textFrame, CFRangeMake(, ), origins);

   int line_y = (int) origins[[linesArray count] -].y;  //最后一行line的原点y坐标

   CGFloat ascent;

   CGFloat descent;

   CGFloat leading;

   CTLineRef line = (CTLineRef) [linesArray objectAtIndex:[linesArray count]-];

   CTLineGetTypographicBounds(line, &ascent, &descent, &leading);

   total_height =  - line_y + (int) descent +;    //+1为了纠正descent转换成int小数点后舍去的值

   CFRelease(textFrame);

   return total_height;

}  

来自：http://blog.csdn.net/iunion/article/details/7925951