NSCharacterSet

学会NSCharacterSet，再也不怕各种字符串处理！！
url出现特殊字符处理-- stringByAddingPercentEncodingWithAllowedCharacters

几个用处
1.编码
2.字符串处理

/** 001 根据一个给定的字符串获取一个NSCharacterSet对象 */
+ (NSCharacterSet *)characterSetWithCharactersInString:(NSString *)aString;

// 使用实例，如上例！！

/** 002 相反字符串限制 【具体见接下的例子】 */
@property (readonly, copy) NSCharacterSet *invertedSet;

/** 003 常用快捷方法集合 （常用的，已满足大多数需求） */
 + controlCharacterSet
 + whitespaceCharacterSet              //空格
 + whitespaceAndNewlineCharacterSet    //空格和换行符
 + decimalDigitCharacterSet            //0-9的数字
 + letterCharacterSet                  //所有字母
 + lowercaseLetterCharacterSet         //小写字母
 + uppercaseLetterCharacterSet         //大写字母
 + alphanumericCharacterSet            //所有数字和字母（大小写不分）
 + punctuationCharacterSet             //标点符号
 + newlineCharacterSet                 //换行

URLFragmentAllowedCharacterSet  "#%<>[\]^`{|}

URLHostAllowedCharacterSet      "#%/<>?@\^`{|}

URLPasswordAllowedCharacterSet  "#%/:<>?@[\]^`{|}

URLPathAllowedCharacterSet      "#%;<>?[\]^`{|}

URLQueryAllowedCharacterSet    "#%<>[\]^`{|}

URLUserAllowedCharacterSet      "#%/:<>?@[\]^`

    // url编码不对%编码
    NSCharacterSet *queryAllowCharacterSet = [NSCharacterSet URLQueryAllowedCharacterSet];
    NSMutableCharacterSet *mSet = [queryAllowCharacterSet mutableCopy];
    [mSet addCharactersInString:@"%"];
    NSString *encodeUrl = [url stringByAddingPercentEncodingWithAllowedCharacters:mSet];

对`#^{}"[]|\<>这些字符编码
NSString *url = @"http://p0.meituan.net/mogu/272621e1bee4bfa74639ff9898ef01b2149126.jpg%40278w_200h_0e_1l%7Cwatermark%3D1%26%26r%3D1%26p%3D9%26x%3D2%26y%3D2%26relative%3D1%26o%3D20";
    
    NSCharacterSet *set = [NSCharacterSet characterSetWithCharactersInString:@"`#^{}\"[]|\\<>"].invertedSet;
    NSString *encodeUrl = [url stringByAddingPercentEncodingWithAllowedCharacters:set];