ios7.0之前用：
[strtestsizeWithFont:ContentFontconstrainedToSize:CGSizeMake(ScreenWeight -20, 1000) lineBreakMode:NSLineBreakByWordWrapping];
ios7之后
CGRect frame = [strtestboundingRectWithSize:CGSizeMake(220,1000) options:NSStringDrawingUsesLineFragmentOriginattributes:@{NSFontAttributeName:[UIFontsystemFontOfSize:10]}context:nil];
attributes参数有：
NSFontAttributeName // UIFont, default Helvetica(Neue) 12
NSParagraphStyleAttributeName // NSParagraphStyle, default defaultParagraphStyle
NSForegroundColorAttributeName // UIColor, default blackColor
NSBackgroundColorAttributeName // UIColor, default nil: no background
NSLigatureAttributeName // NSNumber containing integer, default 1: default ligatures, 0: no ligatures
NSKernAttributeName // NSNumber containing floating point value, in points; amount to modify default kerning. 0 means kerning is disabled.
NSStrikethroughStyleAttributeName ; // NSNumber containing integer, default 0: no strikethrough
NSUnderlineStyleAttributeName // NSNumber containing integer, default 0: no underline
NSStrokeColorAttributeName // UIColor, default nil: same as foreground color
NSStrokeWidthAttributeName // NSNumber containing floating point value, in percent of font point size, default 0: no stroke; positive for stroke alone, negative for stroke and fill (a typical value for outlined text would be 3.0)
NSShadowAttributeName ; // NSShadow, default nil: no shadow
NSTextEffectAttributeName // NSString, default nil: no text effect
NSAttachmentAttributeName // NSTextAttachment, default nil
NSLinkAttributeName // NSURL (preferred) or NSString
NSBaselineOffsetAttributeName // NSNumber containing floating point value, in points; offset from baseline, default 0
NSUnderlineColorAttributeName // UIColor, default nil: same as foreground color
NSStrikethroughColorAttributeName // UIColor, default nil: same as foreground color
NSObliquenessAttributeName // NSNumber containing floating point value; skew to be applied to glyphs, default 0: no skew
NSExpansionAttributeName // NSNumber containing floating point value; log of expansion factor to be applied to glyphs, default 0: no expansion
建立label的时候注意：
① label的font，必须和计算时用的font一样
② label的numberOfLines要设置为零
③ label的宽度设置成计算时设置的宽度一致
注意：在UITextView中用这个计算，得到的高度偏小，主要是UITextView中又默认的边距，需要自己根据具体情况进行相应的调整，特别是在文字比较多的情况下