根据字符串计算宽度

-(CGFloat)WidthWithString:(NSString*)string fontSize:(CGFloat)fontSize height:(CGFloat)height

{

NSDictionary *attrs = @{NSFontAttributeName:[UIFont systemFontOfSize:fontSize]};

return  [string boundingRectWithSize:CGSizeMake(0, height) options:NSStringDrawingTruncatesLastVisibleLine | NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading attributes:attrs context:nil].size.width;

}