///

用NSScaner遍历NSString.

- (NSDictionary*)queryContentsUsingEncoding:(NSStringEncoding)encoding {
  NSCharacterSet* delimiterSet = [NSCharacterSet characterSetWithCharactersInString:@"&;"];
  NSMutableDictionary* pairs = [NSMutableDictionary dictionary];
  NSScanner* scanner = [[[NSScanner alloc] initWithString:self] autorelease];
  while (![scanner isAtEnd]) {
    NSString* pairString = nil;
    [scanner scanUpToCharactersFromSet:delimiterSet intoString:&pairString];
    [scanner scanCharactersFromSet:delimiterSet intoString:NULL];
    NSArray* kvPair = [pairString componentsSeparatedByString:@"="];
    if (kvPair.count == 1 || kvPair.count == 2) {
      NSString* key = [[kvPair objectAtIndex:0]
                       stringByReplacingPercentEscapesUsingEncoding:encoding];
      NSMutableArray* values = [pairs objectForKey:key];
      if (nil == values) {
        values = [NSMutableArray array];
        [pairs setObject:values forKey:key];
      }
      if (kvPair.count == 1) {
        [values addObject:[NSNull null]];

      } else if (kvPair.count == 2) {
        NSString* value = [[kvPair objectAtIndex:1]
                           stringByReplacingPercentEscapesUsingEncoding:encoding];
        [values addObject:value];
      }
    }
  }
  return [NSDictionary dictionaryWithDictionary:pairs];

}

///

对url进行处理

- (id)urlEncoded {
  CFStringRef cfUrlEncodedString = CFURLCreateStringByAddingPercentEscapes(NULL,
                                            (CFStringRef)self,NULL,
                                            (CFStringRef)@"!#$%&'()*+,/:;=?@[]",
                                            kCFStringEncodingUTF8);

  NSString *urlEncoded = [NSString stringWithString:(NSString *)cfUrlEncodedString];
  CFRelease(cfUrlEncodedString);
  return urlEncoded;
}