CoreText绘制文本计算高度

准确计算CoreText高度的方法：

- (int)getAttributedStringHeightWithString:(NSAttributedString *)  string  WidthValue:(int) width
{
   int total_height = 0;
   
   CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)string);    //string 为要计算高度的NSAttributedString
   CGRect drawingRect = CGRectMake(0, 0, width, 1000);  //这里的高要设置足够大
   CGMutablePathRef path = CGPathCreateMutable();
   CGPathAddRect(path, NULL, drawingRect);
   CTFrameRef textFrame = CTFramesetterCreateFrame(framesetter,CFRangeMake(0,0), path, NULL);
   CGPathRelease(path);
   CFRelease(framesetter);
   
   NSArray *linesArray = (NSArray *) CTFrameGetLines(textFrame);
   
   CGPoint origins[[linesArray count]];
   CTFrameGetLineOrigins(textFrame, CFRangeMake(0, 0), origins);
   
   int line_y = (int) origins[[linesArray count] -1].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]-1];
   CTLineGetTypographicBounds(line, &ascent, &descent, &leading);
   
   total_height = 1000 - line_y + (int) descent +1;    //+1为了纠正descent转换成int小数点后舍去的值
   
   CFRelease(textFrame);
   
   return total_height;
   
}