NSString 計算尺寸

NSDictionary *attribute =@{NSFontAttributeName: [UIFontsystemFontOfSize:15]};

CGSize size = [@"tabbar_shaixuan"boundingRectWithSize:CGSizeMake(100,0) options:NSStringDrawingTruncatesLastVisibleLine | NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeadingattributes:attribute context:nil].size;

自定義cell高度：http://www.cocoachina.com/applenews/devnews/2014/0604/8668.html