转自：

 

- ( CGSize ) measureFrame: ( CTFrameRef ) frame forContext: (CGContext *) cgContext

{//frame为排版后的文本

CGPathRef framePath = CTFrameGetPath (frame);

CGRect frameRect = CGPathGetBoundingBox (framePath);

 

CFArrayRef lines = CTFrameGetLines (frame);

CFIndex numLines = CFArrayGetCount (lines);

 

CGFloat maxWidth = 0 ;

CGFloat textHeight = 0 ;

 

// Now run through each line determining the maximum width of all the lines.

// We special case the last line of text. While we've got it's descent handy,

// we'll use it to calculate the typographic height of the text as well.

CFIndex lastLineIndex = numLines - 1 ;

for ( CFIndex index = 0 ; index < numLines; index++)

{

CGFloat ascent, descent, leading, width;

CTLineRef line = ( CTLineRef ) CFArrayGetValueAtIndex (lines, index);

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

 

if (width > maxWidth)

{

maxWidth = width;

}

 

if (index == lastLineIndex)

{

// Get the origin of the last line. We add the descent to this

// (below) to get the bottom edge of the last line of text.

CGPoint lastLineOrigin;

CTFrameGetLineOrigins (frame, CFRangeMake (lastLineIndex, 1 ), &lastLineOrigin);

 

// The height needed to draw the text is from the bottom of the last line

// to the top of the frame.

textHeight =  CGRectGetMaxY (frameRect) - lastLineOrigin. y + descent;

}

}

 

// For some text the exact typographic bounds is a fraction of a point too

// small to fit the text when it is put into a context. We go ahead and round

// the returned drawing area up to the nearest point.  This takes care of the

// discrepencies.

return CGSizeMake ( ceil (maxWidth), ceil (textHeight));

}