[ios] How do I URL encode a string

I have a URL string (NSString) with spaces and & characters. How do I url encode the entire string (including the & ampersand character and spaces)?

ios 7 update

NSString *encode = [string stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];

NSString *decode = [encode stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

So many answers but didn't work for me, so I tried the following:

fun simpleServiceCall(for serviceUrl: String, appendToUrl: String) { 
    let urlString: String = serviceUrl + appendToUrl.addingPercentEncoding(withAllowedCharacters: .urlPathAllowed)!     

    let finalUrl = URL(string: urlString)!

    //continue to execute your service call... 
}

Hopefully it'll help someone. thanks

In Swift 3, please try out below:

let stringURL = "YOUR URL TO BE ENCODE";
let encodedURLString = stringURL.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed)
print(encodedURLString)

Since, stringByAddingPercentEscapesUsingEncoding encodes non URL characters but leaves the reserved characters (like !*'();:@&=+$,/?%#[]), You can encode the url like the following code:

let stringURL = "YOUR URL TO BE ENCODE";
let characterSetTobeAllowed = (CharacterSet(charactersIn: "!*'();:@&=+$,/?%#[] ").inverted)
if let encodedURLString = stringURL.addingPercentEncoding(withAllowedCharacters: characterSetTobeAllowed) {
    print(encodedURLString)
}

Try to use stringByAddingPercentEncodingWithAllowedCharacters method with [NSCharacterSet URLUserAllowedCharacterSet] it will cover all the cases

Objective C

NSString *value = @"Test / Test";
value = [value stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLUserAllowedCharacterSet]];

swift

var value = "Test / Test"
value.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLUserAllowedCharacterSet())

Output

Test%20%2F%20Test

Apple's advice, in the 10.11 release notes, is:

If you need to percent-encode an entire URL string, you can use this code to encode a NSString intended to be a URL (in urlStringToEncode):

NSString *percentEncodedURLString =
  [[NSURL URLWithDataRepresentation:[urlStringToEncode dataUsingEncoding:NSUTF8StringEncoding] relativeToURL:nil] relativeString];

Use NSURLComponents to encode HTTP GET parameters:

    var urlComponents = NSURLComponents(string: "https://www.google.de/maps/")!
    urlComponents.queryItems = [
        NSURLQueryItem(name: "q", value: String(51.500833)+","+String(-0.141944)),
        NSURLQueryItem(name: "z", value: String(6))
    ]
    urlComponents.URL     // returns https://www.google.de/maps/?q=51.500833,-0.141944&z=6

http://www.ralfebert.de/snippets/ios/encoding-nsurl-get-parameters/

For the php function urlencode encoding a NSString to a cString with UTF8Encode, like [NSString UTF8String] was not working.

Here is my custom objective c NSString+ASCIIencode Category with works with all ASCII values 0..255

Header

#import <Cocoa/Cocoa.h>

@interface NSString (ASCIIEncode)

- (const char*)ASCIIEncode;

@end

Implementation

#import "NSString+ASCIIEncode.h"

@implementation NSString (ASCIIEncode)

- (const char*)ASCIIEncode {
    
    static char output[1024];
    
    // https://tools.piex.at/ascii-tabelle/
    // https://www.ionos.de/digitalguide/server/knowhow/ascii-american-standard-code-for-information-interchange/
    
    NSMutableArray *ascii = [NSMutableArray new];
// Hex
// 000                          Dez Hex
    [ascii addObject:@"\0"]; // 000 000 NUL
    [ascii addObject:@( 1)]; // 001 001 SOH
    [ascii addObject:@( 2)]; // 002 002 STX
    [ascii addObject:@( 3)]; // 003 003 ETX
    [ascii addObject:@( 4)]; // 004 004 EOT
    [ascii addObject:@( 5)]; // 005 005 ENQ
    [ascii addObject:@( 6)]; // 006 006 ACK
    [ascii addObject:@"\a"]; // 007 007 BEL
    [ascii addObject:@"\b"]; // 008 008 BS
    [ascii addObject:@( 9)]; // 009 009 TAB
    [ascii addObject:@"\n"]; // 010 00A LF
    [ascii addObject:@(11)]; // 011 00B VT
    [ascii addObject:@(12)]; // 012 00C FF
    [ascii addObject:@"\r"]; // 013 00D CR
    [ascii addObject:@(14)]; // 014 00E SO
    [ascii addObject:@(15)]; // 015 00F NAK
// 010
    [ascii addObject:@(16)]; // 016 010 DLE
    [ascii addObject:@(17)]; // 017 011 DC1
    [ascii addObject:@(18)]; // 018 012 DC2
    [ascii addObject:@(19)]; // 019 013 DC3
    [ascii addObject:@(20)]; // 020 014 DC4
    [ascii addObject:@(21)]; // 021 015 NAK
    [ascii addObject:@(22)]; // 022 016 SYN
    [ascii addObject:@(23)]; // 023 017 ETB
    [ascii addObject:@(24)]; // 024 018 CAN
    [ascii addObject:@(25)]; // 025 019 EM
    [ascii addObject:@(26)]; // 026 01A SUB
    [ascii addObject:@(27)]; // 027 01B ESC
    [ascii addObject:@(28)]; // 028 01C FS
    [ascii addObject:@(29)]; // 029 01D GS
    [ascii addObject:@(30)]; // 030 01E RS
    [ascii addObject:@(31)]; // 031 01F US
// 020
    [ascii addObject:@" "];  // 032 020 Space
    [ascii addObject:@"!"];  // 033 021
    [ascii addObject:@"\""]; // 034 022
    [ascii addObject:@"#"];  // 035 023
    [ascii addObject:@"$"];  // 036 024
    [ascii addObject:@"%"];  // 037 025
    [ascii addObject:@"&"];  // 038 026
    [ascii addObject:@"'"];  // 039 027
    [ascii addObject:@"("];  // 040 028
    [ascii addObject:@")"];  // 041 029
    [ascii addObject:@"*"];  // 042 02A
    [ascii addObject:@"+"];  // 043 02B
    [ascii addObject:@","];  // 044 02C
    [ascii addObject:@"-"];  // 045 02D
    [ascii addObject:@"."];  // 046 02E
    [ascii addObject:@"/"];  // 047 02F
// 030
    [ascii addObject:@"0"];  // 048 030
    [ascii addObject:@"1"];  // 049 031
    [ascii addObject:@"2"];  // 050 032
    [ascii addObject:@"3"];  // 051 033
    [ascii addObject:@"4"];  // 052 034
    [ascii addObject:@"5"];  // 053 035
    [ascii addObject:@"6"];  // 054 036
    [ascii addObject:@"7"];  // 055 037
    [ascii addObject:@"8"];  // 056 038
    [ascii addObject:@"9"];  // 057 039
    [ascii addObject:@":"];  // 058 03A
    [ascii addObject:@";"];  // 059 03B
    [ascii addObject:@"<"];  // 060 03C
    [ascii addObject:@"="];  // 061 03D
    [ascii addObject:@">"];  // 062 03E
    [ascii addObject:@"?"];  // 063 03F
// 040
    [ascii addObject:@"@"];  // 064 040
    [ascii addObject:@"A"];  // 065 041
    [ascii addObject:@"B"];  // 066 042
    [ascii addObject:@"C"];  // 067 043
    [ascii addObject:@"D"];  // 068 044
    [ascii addObject:@"E"];  // 069 045
    [ascii addObject:@"F"];  // 070 046
    [ascii addObject:@"G"];  // 071 047
    [ascii addObject:@"H"];  // 072 048
    [ascii addObject:@"I"];  // 073 049
    [ascii addObject:@"J"];  // 074 04A
    [ascii addObject:@"K"];  // 075 04B
    [ascii addObject:@"L"];  // 076 04C
    [ascii addObject:@"M"];  // 077 04D
    [ascii addObject:@"N"];  // 078 04E
    [ascii addObject:@"O"];  // 079 04F
// 050
    [ascii addObject:@"P"];  // 080 050
    [ascii addObject:@"Q"];  // 081 051
    [ascii addObject:@"R"];  // 082 052
    [ascii addObject:@"S"];  // 083 053
    [ascii addObject:@"T"];  // 084 054
    [ascii addObject:@"U"];  // 085 055
    [ascii addObject:@"V"];  // 086 056
    [ascii addObject:@"W"];  // 087 057
    [ascii addObject:@"X"];  // 088 058
    [ascii addObject:@"Y"];  // 089 059
    [ascii addObject:@"Z"];  // 090 05A
    [ascii addObject:@"["];  // 091 05B
    [ascii addObject:@"\\"]; // 092 05C
    [ascii addObject:@"]"];  // 093 05D
    [ascii addObject:@"^"];  // 094 05E
    [ascii addObject:@"_"];  // 095 05F
// 060
    [ascii addObject:@"`"];  // 096 060
    [ascii addObject:@"a"];  // 097 061
    [ascii addObject:@"b"];  // 098 062
    [ascii addObject:@"c"];  // 099 063
    [ascii addObject:@"d"];  // 100 064
    [ascii addObject:@"e"];  // 101 065
    [ascii addObject:@"f"];  // 102 066
    [ascii addObject:@"g"];  // 103 067
    [ascii addObject:@"h"];  // 104 068
    [ascii addObject:@"i"];  // 105 069
    [ascii addObject:@"j"];  // 106 06A
    [ascii addObject:@"k"];  // 107 06B
    [ascii addObject:@"l"];  // 108 06C
    [ascii addObject:@"m"];  // 109 06D
    [ascii addObject:@"n"];  // 110 06E
    [ascii addObject:@"o"];  // 111 06F
// 070
    [ascii addObject:@"p"];  // 112 070
    [ascii addObject:@"q"];  // 113 071
    [ascii addObject:@"r"];  // 114 072
    [ascii addObject:@"s"];  // 115 073
    [ascii addObject:@"t"];  // 116 074
    [ascii addObject:@"u"];  // 117 075
    [ascii addObject:@"v"];  // 118 076
    [ascii addObject:@"w"];  // 119 077
    [ascii addObject:@"x"];  // 120 078
    [ascii addObject:@"y"];  // 121 079
    [ascii addObject:@"z"];  // 122 07A
    [ascii addObject:@"{"];  // 123 07B
    [ascii addObject:@"|"];  // 124 07C
    [ascii addObject:@"}"];  // 125 07D
    [ascii addObject:@"~"];  // 126 07E
    [ascii addObject:@(127)];// 127 07F DEL
// 080
    [ascii addObject:@"€"];  // 128 080
    [ascii addObject:@(129)];// 129 081
    [ascii addObject:@"‚"];  // 130 082
    [ascii addObject:@"ƒ"];  // 131 083
    [ascii addObject:@"„"];  // 132 084
    [ascii addObject:@"…"];  // 133 085
    [ascii addObject:@"†"];  // 134 086
    [ascii addObject:@"‡"];  // 135 087
    [ascii addObject:@"ˆ"];  // 136 088
    [ascii addObject:@"‰"];  // 137 089
    [ascii addObject:@"Š"];  // 138 08A
    [ascii addObject:@"‹"];  // 139 08B
    [ascii addObject:@"Œ"];  // 140 08C
    [ascii addObject:@(141)];// 141 08D
    [ascii addObject:@"Ž"];  // 142 08E
    [ascii addObject:@(143)];  // 143 08F
// 090
    [ascii addObject:@(144)];// 144 090
    [ascii addObject:@"‘"];  // 145 091
    [ascii addObject:@"’"];  // 146 092
    [ascii addObject:@"“"];  // 147 093
    [ascii addObject:@"”"];  // 148 094
    [ascii addObject:@"•"];  // 149 095
    [ascii addObject:@"–"];  // 150 096
    [ascii addObject:@"—"];  // 151 097
    [ascii addObject:@"˜"];  // 152 098
    [ascii addObject:@"™"];  // 153 099
    [ascii addObject:@"š"];  // 154 09A
    [ascii addObject:@"›"];  // 155 09B
    [ascii addObject:@"œ"];  // 156 09C
    [ascii addObject:@(157)];// 157 09D
    [ascii addObject:@"ž"];  // 158 09E
    [ascii addObject:@"Ÿ"];  // 159 09F
// 0A0
    [ascii addObject:@(160)];// 160 0A0
    [ascii addObject:@"¡"];  // 161 0A1
    [ascii addObject:@"¢"];  // 162 0A2
    [ascii addObject:@"£"];  // 163 0A3
    [ascii addObject:@"¤"];  // 164 0A4
    [ascii addObject:@"¥"];  // 165 0A5
    [ascii addObject:@"¦"];  // 166 0A6
    [ascii addObject:@"§"];  // 167 0A7
    [ascii addObject:@"¨"];  // 168 0A8
    [ascii addObject:@"©"];  // 169 0A9
    [ascii addObject:@"ª"];  // 170 0AA
    [ascii addObject:@"«"];  // 171 0AB
    [ascii addObject:@"¬"];  // 172 0AC
    [ascii addObject:@(173)];// 173 0AD
    [ascii addObject:@"®"];  // 174 0AE
    [ascii addObject:@"¯"];  // 175 0AF
// 0B0
    [ascii addObject:@"°"];  // 176 0B0
    [ascii addObject:@"±"];  // 177 0B1
    [ascii addObject:@"²"];  // 178 0B2
    [ascii addObject:@"³"];  // 179 0B3
    [ascii addObject:@"´"];  // 180 0B4
    [ascii addObject:@"µ"];  // 181 0B5
    [ascii addObject:@"¶"];  // 182 0B6
    [ascii addObject:@"·"];  // 183 0B7
    [ascii addObject:@"¸"];  // 184 0B8
    [ascii addObject:@"¹"];  // 185 0B9
    [ascii addObject:@"º"];  // 186 0BA
    [ascii addObject:@"»"];  // 187 0BB
    [ascii addObject:@"¼"];  // 188 0BC
    [ascii addObject:@"½"];  // 189 0BD
    [ascii addObject:@"¾"];  // 190 0BE
    [ascii addObject:@"¿"];  // 191 0BF
// 0C0
    [ascii addObject:@"À"];  // 192 0C0
    [ascii addObject:@"Á"];  // 193 0C1
    [ascii addObject:@"Â"];  // 194 0C2
    [ascii addObject:@"Ã"];  // 195 0C3
    [ascii addObject:@"Ä"];  // 196 0C4
    [ascii addObject:@"Å"];  // 197 0C5
    [ascii addObject:@"Æ"];  // 198 0C6
    [ascii addObject:@"Ç"];  // 199 0C7
    [ascii addObject:@"È"];  // 200 0C8
    [ascii addObject:@"É"];  // 201 0C9
    [ascii addObject:@"Ê"];  // 202 0CA
    [ascii addObject:@"Ë"];  // 203 0CB
    [ascii addObject:@"Ì"];  // 204 0CC
    [ascii addObject:@"Í"];  // 205 0CD
    [ascii addObject:@"Î"];  // 206 0CE
    [ascii addObject:@"Ï"];  // 207 0CF
// 0D0
    [ascii addObject:@"Ð"];  // 208 0D0
    [ascii addObject:@"Ñ"];  // 209 0D1
    [ascii addObject:@"Ò"];  // 210 0D2
    [ascii addObject:@"Ó"];  // 211 0D3
    [ascii addObject:@"Ô"];  // 212 0D4
    [ascii addObject:@"Õ"];  // 213 0D5
    [ascii addObject:@"Ö"];  // 214 0D6
    [ascii addObject:@"×"];  // 215 0D7
    [ascii addObject:@"Ø"];  // 216 0D8
    [ascii addObject:@"Ù"];  // 217 0D9
    [ascii addObject:@"Ú"];  // 218 0DA
    [ascii addObject:@"Û"];  // 219 0DB
    [ascii addObject:@"Ü"];  // 220 0DC
    [ascii addObject:@"Ý"];  // 221 0DD
    [ascii addObject:@"Þ"];  // 222 0DE
    [ascii addObject:@"ß"];  // 223 0DF
// 0E0
    [ascii addObject:@"à"];  // 224 0E0
    [ascii addObject:@"á"];  // 225 0E1
    [ascii addObject:@"â"];  // 226 0E2
    [ascii addObject:@"ã"];  // 227 0E3
    [ascii addObject:@"ä"];  // 228 0E4
    [ascii addObject:@"å"];  // 229 0E5
    [ascii addObject:@"æ"];  // 230 0E6
    [ascii addObject:@"ç"];  // 231 0E7
    [ascii addObject:@"è"];  // 232 0E8
    [ascii addObject:@"é"];  // 233 0E9
    [ascii addObject:@"ê"];  // 234 0EA
    [ascii addObject:@"ë"];  // 235 0EB
    [ascii addObject:@"ì"];  // 236 0EC
    [ascii addObject:@"í"];  // 237 0ED
    [ascii addObject:@"î"];  // 238 0EE
    [ascii addObject:@"ï"];  // 239 0EF
// 0F0
    [ascii addObject:@"ð"];  // 240 0F0
    [ascii addObject:@"ñ"];  // 241 0F1
    [ascii addObject:@"ò"];  // 242 0F2
    [ascii addObject:@"ó"];  // 243 0F3
    [ascii addObject:@"ô"];  // 244 0F4
    [ascii addObject:@"õ"];  // 245 0F5
    [ascii addObject:@"ö"];  // 246 0F6
    [ascii addObject:@"÷"];  // 247 0F7
    [ascii addObject:@"ø"];  // 248 0F8
    [ascii addObject:@"ù"];  // 249 0F9
    [ascii addObject:@"ú"];  // 250 0FA
    [ascii addObject:@"û"];  // 251 0FB
    [ascii addObject:@"ü"];  // 252 0FC
    [ascii addObject:@"ý"];  // 253 0FD
    [ascii addObject:@"þ"];  // 254 0FE
    [ascii addObject:@"ÿ"];  // 255 0FF
    
    NSInteger i;
    
    for (i=0; i < self.length; i++) {
        
        NSRange range;
        range.location = i;
        range.length = 1;
        
        NSString *charString = [self substringWithRange:range];
        
        for (NSInteger asciiIdx=0; asciiIdx < ascii.count; asciiIdx++) {
            
            if ([charString isEqualToString:ascii[asciiIdx]]) {
                unsigned char c = (unsigned char)asciiIdx;
                output[i] = c;
                break;
            }
            
        }
    }
    
    // Don't forget string termination
    output[i] = 0;

    return (const char*)&output[0];
}

@end

New APIs have been added since the answer was selected; You can now use NSURLUtilities. Since different parts of URLs allow different characters, use the applicable character set. The following example encodes for inclusion in the query string:

encodedString = [myString stringByAddingPercentEncodingWithAllowedCharacters:NSCharacterSet.URLQueryAllowedCharacterSet];

To specifically convert '&', you'll need to remove it from the url query set or use a different set, as '&' is allowed in a URL query:

NSMutableCharacterSet *chars = NSCharacterSet.URLQueryAllowedCharacterSet.mutableCopy;
[chars removeCharactersInRange:NSMakeRange('&', 1)]; // %26
encodedString = [myString stringByAddingPercentEncodingWithAllowedCharacters:chars];

I opted to use the CFURLCreateStringByAddingPercentEscapes call as given by accepted answer, however in newest version of XCode (and IOS), it resulted in an error, so used the following instead:

NSString *apiKeyRaw = @"79b|7Qd.jW=])(fv|M&W0O|3CENnrbNh4}2E|-)J*BCjCMrWy%dSfGs#A6N38Fo~";

NSString *apiKey = (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL, (CFStringRef)apiKeyRaw, NULL, (CFStringRef)@"!*'();:@&=+$,/?%#[]", kCFStringEncodingUTF8));

-(NSString *)encodeUrlString:(NSString *)string {
  return CFBridgingRelease(
                    CFURLCreateStringByAddingPercentEscapes(
                        kCFAllocatorDefault,
                        (__bridge CFStringRef)string,
                        NULL,
                        CFSTR("!*'();:@&=+$,/?%#[]"),
                        kCFStringEncodingUTF8)
                    );
}

according to the following blog

Here's a production-ready flexible approach in Swift 5.x:

public extension CharacterSet {

    static let urlQueryParameterAllowed = CharacterSet.urlQueryAllowed.subtracting(CharacterSet(charactersIn: "&?"))

    static let urlQueryDenied           = CharacterSet.urlQueryAllowed.inverted()
    static let urlQueryKeyValueDenied   = CharacterSet.urlQueryParameterAllowed.inverted()
    static let urlPathDenied            = CharacterSet.urlPathAllowed.inverted()
    static let urlFragmentDenied        = CharacterSet.urlFragmentAllowed.inverted()
    static let urlHostDenied            = CharacterSet.urlHostAllowed.inverted()

    static let urlDenied                = CharacterSet.urlQueryDenied
        .union(.urlQueryKeyValueDenied)
        .union(.urlPathDenied)
        .union(.urlFragmentDenied)
        .union(.urlHostDenied)


    func inverted() -> CharacterSet {
        var copy = self
        copy.invert()
        return copy
    }
}



public extension String {
    func urlEncoded(denying deniedCharacters: CharacterSet = .urlDenied) -> String? {
        return addingPercentEncoding(withAllowedCharacters: deniedCharacters.inverted())
    }
}

Example usage:

print("Hello, World!".urlEncoded()!)
print("You&Me?".urlEncoded()!)
print("#Blessed 100%".urlEncoded()!)
print("Pride and Prejudice".urlEncoded(denying: .uppercaseLetters)!)

Output:

Hello,%20World!
You%26Me%3F
%23Blessed%20100%25
%50ride and %50rejudice

This one is working for me.

func stringByAddingPercentEncodingForFormData(plusForSpace: Bool=false) -> String? {
    let unreserved = "*-._"
    let allowed = NSMutableCharacterSet.alphanumericCharacterSet()
    allowed.addCharactersInString(unreserved)

    if plusForSpace {
        allowed.addCharactersInString(" ")
    }

    var encoded = stringByAddingPercentEncodingWithAllowedCharacters(allowed)
    if plusForSpace {
        encoded = encoded?.stringByReplacingOccurrencesOfString(" ",
                                                                withString: "+")
    }
    return encoded
}

I found the above function from this link: http://useyourloaf.com/blog/how-to-percent-encode-a-url-string/

You can also use this function with swift extension. Please let me know if there is any issue.

In my case where the last component was Arabic letters I did the following in Swift 2.2:

extension String {

 func encodeUTF8() -> String? {

    //If I can create an NSURL out of the string nothing is wrong with it
    if let _ = NSURL(string: self) {

        return self
    }

    //Get the last component from the string this will return subSequence
    let optionalLastComponent = self.characters.split { $0 == "/" }.last


    if let lastComponent = optionalLastComponent {

        //Get the string from the sub sequence by mapping the characters to [String] then reduce the array to String
        let lastComponentAsString = lastComponent.map { String($0) }.reduce("", combine: +)


        //Get the range of the last component
        if let rangeOfLastComponent = self.rangeOfString(lastComponentAsString) {
            //Get the string without its last component
            let stringWithoutLastComponent = self.substringToIndex(rangeOfLastComponent.startIndex)


            //Encode the last component
            if let lastComponentEncoded = lastComponentAsString.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.alphanumericCharacterSet()) {


            //Finally append the original string (without its last component) to the encoded part (encoded last component)
            let encodedString = stringWithoutLastComponent + lastComponentEncoded

                //Return the string (original string/encoded string)
                return encodedString
            }
        }
    }

    return nil;
}
}

usage:

let stringURL = "http://xxx.dev.com/endpoint/nonLatinCharacters"

if let encodedStringURL = stringURL.encodeUTF8() {

    if let url = NSURL(string: encodedStringURL) {

      ...
    }

} 

//This is without test

NSMutableCharacterSet* set = [[NSCharacterSet alphanumericCharacterSet] mutableCopy];
[set addCharactersInString:@"-_.~"];
NSString *encode = [test stringByAddingPercentEncodingWithAllowedCharacters:set];

In swift 3:

// exclude alpha and numeric == "full" encoding
stringUrl = stringUrl.addingPercentEncoding(withAllowedCharacters: .alphanumerics)!;

// exclude hostname and symbols &,/ and etc
stringUrl = stringUrl.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed)!;

swift code based on chown's objc answer in this thread.

extension String {
    func urlEncode() -> String {
        return CFURLCreateStringByAddingPercentEscapes(
            nil,
            self,
            nil,
            "!*'();:@&=+$,/?%#[]",
            CFStringBuiltInEncodings.UTF8.rawValue
        )
    }
}

After reading all the answers for this topic and the (wrong) accepted one, I want to add my contribution.

IF the target is iOS7+, and in 2017 it should since XCode makes really hard to deliver compatibility under iOS8, the best way, thread safe, fast, amd will full UTF-8 support to do this is:

(Objective C code)

@implementation NSString (NSString_urlencoding)

- (NSString *)urlencode {
    static NSMutableCharacterSet *chars = nil;
    static dispatch_once_t pred;

    if (chars)
        return [self stringByAddingPercentEncodingWithAllowedCharacters:chars];

    // to be thread safe
    dispatch_once(&pred, ^{
        chars = NSCharacterSet.URLQueryAllowedCharacterSet.mutableCopy;
        [chars removeCharactersInString:@"!*'();:@&=+$,/?%#[]"];
    });
    return [self stringByAddingPercentEncodingWithAllowedCharacters:chars];
}
@end

This will extend NSString, will exclude RFC forbidden characters, support UTF-8 characters, and let you use things like:

NSString *myusername = "I'm[evil]&want(to)break!!!$->àéìòù";
NSLog(@"Source: %@ -> Dest: %@", myusername, [myusername urlencode]);

That will print on your debug console:

Source: I'm[evil]&want(to)break!!!$->àéìòù -> Dest: I%27m%5Bevil%5D%26want%28to%29break%21%21%21%24-%3E%C3%A0%C3%A9%C3%AC%C3%B2%C3%B9

... note also the use of dispatch_once to avoid multiple initializations in multithread environments.

This might be helpful

NSString *sampleUrl = @"http://www.google.com/search.jsp?params=Java Developer";
NSString* encodedUrl = [sampleUrl stringByAddingPercentEscapesUsingEncoding:
 NSUTF8StringEncoding];

For iOS 7+, the recommended way is:

NSString* encodedUrl = [sampleUrl stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];

You can choose the allowed character set as per the requirement of the URL component.

I faced a similar problem passing complex strings as a POST parameter. My strings can contain Asian characters, spaces, quotes and all sorts of special characters. The solution I eventually found was to convert my string into the matching series of unicodes, e.g. "Hu0040Hu0020Hu03f5...." using [NSString stringWithFormat:@"Hu%04x",[string characterAtIndex:i]] to get the Unicode from each character in the original string. The same can be done in Java.

This string can be safely passed as a POST parameter.

On the server side (PHP), I change all the "H" to "\" and I pass the resulting string to json_decode. Final step is to escape single quotes before storing the string into MySQL.

This way I can store any UTF8 string on my server.

Swift 2.0 Example (iOS 9 Compatiable)

extension String {

  func stringByURLEncoding() -> String? {

    let characters = NSCharacterSet.URLQueryAllowedCharacterSet().mutableCopy() as! NSMutableCharacterSet

    characters.removeCharactersInString("&")

    guard let encodedString = self.stringByAddingPercentEncodingWithAllowedCharacters(characters) else {
      return nil
    }

    return encodedString

  }

}

This code helped me for encoding special characters

NSString* encPassword = [password stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet alphanumericCharacterSet]];

For individual www form-encoded query parameters, I made a category on NSString:

- (NSString*)WWWFormEncoded{
     NSMutableCharacterSet *chars = NSCharacterSet.alphanumericCharacterSet.mutableCopy;
     [chars addCharactersInString:@" "];
     NSString* encodedString = [self stringByAddingPercentEncodingWithAllowedCharacters:chars];
     encodedString = [encodedString stringByReplacingOccurrencesOfString:@" " withString:@"+"];
     return encodedString;
}