计算string高度

一、CTFramesetterSuggestFrameSizeWithConstraints计算文本显示所占区域修正方法

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

CTFontRef ctFont = CTFontCreateWithName((CFStringRef) uiFont.fontName, uiFont.pointSize, NULL);

CGFloat leading = uiFont.lineHeight - uiFont.ascender + uiFont.descender;

CTParagraphStyleSetting paragraphSettings[1] = { kCTParagraphStyleSpecifierLineSpacingAdjustment, sizeof (CGFloat), &leading };

CTParagraphStyleRef  paragraphStyle = CTParagraphStyleCreate(paragraphSettings, 1);

CFRange textRange = CFRangeMake(0, text.length);

//  Create an empty mutable string big enough to hold our test

CFMutableAttributedStringRef string = CFAttributedStringCreateMutable(kCFAllocatorDefault, text.length);

//  Inject our text into it

CFAttributedStringReplaceString(string, CFRangeMake(0, 0), (CFStringRef) text);

//  Apply our font and line spacing attributes over the span

CFAttributedStringSetAttribute(string, textRange, kCTFontAttributeName, ctFont);

CFAttributedStringSetAttribute(string, textRange, kCTParagraphStyleAttributeName, paragraphStyle);

CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(string);

CFRange range;

CGSize sizeAfterRender = CTFramesetterSuggestFrameSizeWithConstraints(framesetter, textRange, nil,

CGSizeMake(300, 1000000)

, &range);

二、ios7.0以上方法

NSDictionary *attributes = @{NSFontAttributeName:font};

CGSize lablesize = [showtext  boundingRectWithSize:CGSizeMake(300,1000000) options:NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading

attributes:attributes

context:nil].size;