// urlencode
- (NSString *)urlEncodedString {
    NSString *encodedString = (NSString *)
    CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
                                                              (CFStringRef)self,
                                                              (CFStringRef)@"!$&'()*+,-./:;=?@_~%#[]",
                                                              NULL,
                                                              kCFStringEncodingUTF8));
    return encodedString;
}

// urldecode
- (NSString *)urlDecodeString {
    NSString *decodedString  = (__bridge_transfer NSString *)CFURLCreateStringByReplacingPercentEscapesUsingEncoding(NULL,
                                                                                                                     (__bridge CFStringRef)self,
                                                                                                                     CFSTR(""),
                                                                                                                     CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding));
    return decodedString;
}