单行文字
CGSize size =[content sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:14]}];
多行文字
CGSize size = [content boundingRectWithSize:CGSizeMake(kScreen_Width, MAXFLOAT) options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:14]} context:nil].size;
