How to get the public IP address of the device

I have used ALSystemUtilities in the past. You basically have to make a call externally to find this out.

+ (NSString *)externalIPAddress {
    // Check if we have an internet connection then try to get the External IP Address
    if (![self connectedViaWiFi] && ![self connectedVia3G]) {
        // Not connected to anything, return nil
        return nil;
    }

    // Get the external IP Address based on dynsns.org
    NSError *error = nil;
    NSString *theIpHtml = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://www.dyndns.org/cgi-bin/check_ip.cgi"]
                                                   encoding:NSUTF8StringEncoding
                                                      error:&error];
    if (!error) {
        NSUInteger  an_Integer;
        NSArray *ipItemsArray;
        NSString *externalIP;
        NSScanner *theScanner;
        NSString *text = nil;

        theScanner = [NSScanner scannerWithString:theIpHtml];

        while ([theScanner isAtEnd] == NO) {

            // find start of tag
            [theScanner scanUpToString:@"<" intoString:NULL] ;

            // find end of tag
            [theScanner scanUpToString:@">" intoString:&text] ;

            // replace the found tag with a space
            //(you can filter multi-spaces out later if you wish)
            theIpHtml = [theIpHtml stringByReplacingOccurrencesOfString:
                         [ NSString stringWithFormat:@"%@>", text]
                                                             withString:@" "] ;
            ipItemsArray = [theIpHtml  componentsSeparatedByString:@" "];
            an_Integer = [ipItemsArray indexOfObject:@"Address:"];
            externalIP =[ipItemsArray objectAtIndex:++an_Integer];
        }
        // Check that you get something back
        if (externalIP == nil || externalIP.length <= 0) {
            // Error, no address found
            return nil;
        }
        // Return External IP
        return externalIP;
    } else {
        // Error, no address found
        return nil;
    }
}

Source from ALSystemUtilities

It's as simple as this:

NSString *publicIP = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"https://icanhazip.com/"] encoding:NSUTF8StringEncoding error:nil];
publicIP = [publicIP stringByTrimmingCharactersInSet:[NSCharacterSet newlineCharacterSet]]; // IP comes with a newline for some reason

Thanks @Tarek for his answer

Here, code in Swift 4 version

func getPublicIPAddress() -> String {
    var publicIP = ""
    do {
        try publicIP = String(contentsOf: URL(string: "https://www.bluewindsolution.com/tools/getpublicip.php")!, encoding: String.Encoding.utf8)
        publicIP = publicIP.trimmingCharacters(in: CharacterSet.whitespaces)
    }
    catch {
        print("Error: \(error)")
    }
    return publicIP
}

NOTE1: To get public IP address, we must have external site to return public IP. The website I use is business company website, so, it will be their until the business gone.

NOTE2: You can made some site by yourself, however, Apple require HTTPS site to be able to use this function.