NSURL pull out a single value for a key in a parameter string

So many custom url parsers here, remember NSURLComponents is your friend!

Here is an example where I pull out a url encoded parameter for "page"

Swift

let myURL = "www.something.com?page=2"

var pageNumber : Int?
if let queryItems = NSURLComponents(string: myURL)?.queryItems {
    for item in queryItems {
        if item.name == "page" {
           if let itemValue = item.value {
               pageNumber = Int(itemValue)
           }
        }
    }
}
print("Found page number: \(pageNumber)")

Objective-C

NSString *myURL = @"www.something.com?page=2";
NSURLComponents *components = [NSURLComponents componentsWithString:myURL];
NSNumber *page = nil;
for(NSURLQueryItem *item in components.queryItems)
{
    if([item.name isEqualToString:@"page"])
        page = [NSNumber numberWithInteger:item.value.integerValue];
}

"Why reinvent the wheel!" - Someone Smart

I'm pretty sure you have to parse it yourself. However, it's not too bad:

NSString * q = [myURL query];
NSArray * pairs = [q componentsSeparatedByString:@"&"];
NSMutableDictionary * kvPairs = [NSMutableDictionary dictionary];
for (NSString * pair in pairs) {
  NSArray * bits = [pair componentsSeparatedByString:@"="];
  NSString * key = [[bits objectAtIndex:0] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
  NSString * value = [[bits objectAtIndex:1] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
  [kvPairs setObject:value forKey:key];
}

NSLog(@"y = %@", [kvPairs objectForKey:@"y"]);

In Swift you can use NSURLComponents to parse the query string of an NSURL into an [AnyObject].

You can then create a dictionary from it (or access the items directly) to get at the key/value pairs. As an example this is what I am using to parse a NSURL variable url:

let urlComponents = NSURLComponents(URL: url, resolvingAgainstBaseURL: false)
let items = urlComponents?.queryItems as [NSURLQueryItem]
var dict = NSMutableDictionary()
for item in items{
    dict.setValue(item.value, forKey: item.name)
}
println(dict["x"])

I've been using this Category: https://github.com/carlj/NSURL-Parameters.

It's small and easy to use:

#import "NSURL+Parameters.h"
...
NSURL *url = [NSURL URLWithString:@"http://foo.bar.com?paramA=valueA&paramB=valueB"];
NSString *paramA = url[@"paramA"];
NSString *paramB = url[@"paramB"];

You can use Google Toolbox for Mac. It adds a function to NSString to convert query string to a dictionary.

http://code.google.com/p/google-toolbox-for-mac/

It works like a charm

        NSDictionary * d = [NSDictionary gtm_dictionaryWithHttpArgumentsString:[[request URL] query]];

Here's a Swift 2.0 extension that provides simple access to parameters:

extension NSURL {
    var params: [String: String] {
        get {
            let urlComponents = NSURLComponents(URL: self, resolvingAgainstBaseURL: false)
            var items = [String: String]()
            for item in urlComponents?.queryItems ?? [] {
                items[item.name] = item.value ?? ""
            }
            return items
        }
    }
} 

Sample usage:

let url = NSURL(string: "http://google.com?test=dolphins")
if let testParam = url.params["test"] {
    print("testParam: \(testParam)")
}

I wrote a simple category to extend NSString/NSURL that lets you extract URL query parameters individually or as a dictionary of key/value pairs:

https://github.com/nicklockwood/RequestUtils

I did it using a category method based on @Dimitris solution

#import "NSURL+DictionaryValue.h"

@implementation NSURL (DictionaryValue)
-(NSDictionary *)dictionaryValue
{
NSString *string =  [[self.absoluteString stringByReplacingOccurrencesOfString:@"+" withString:@" "]
                     stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSScanner *scanner = [NSScanner scannerWithString:string];
[scanner setCharactersToBeSkipped:[NSCharacterSet characterSetWithCharactersInString:@"&?"]];

NSString *temp;
NSMutableDictionary *dict = [[[NSMutableDictionary alloc] init] autorelease];
[scanner scanUpToString:@"?" intoString:nil];       //ignore the beginning of the string and skip to the vars
while ([scanner scanUpToString:@"&" intoString:&temp]) 
{
    NSArray *parts = [temp componentsSeparatedByString:@"="];
    if([parts count] == 2)
    {
        [dict setObject:[parts objectAtIndex:1] forKey:[parts objectAtIndex:0]];
    }
}

return dict;
}
@end

All of the current answers are version specific or needlessly wasteful. Why create a dictionary if you only want one value?

Here's a simple answer that supports all iOS versions:

- (NSString *)getQueryParam:(NSString *)name  fromURL:(NSURL *)url
{
    if (url)
    {
        NSArray *urlComponents = [url.query componentsSeparatedByString:@"&"];
        for (NSString *keyValuePair in urlComponents)
        {
            NSArray *pairComponents = [keyValuePair componentsSeparatedByString:@"="];
            NSString *key = [[pairComponents firstObject] stringByRemovingPercentEncoding];

            if ([key isEqualToString:name])
            {
                return [[pairComponents lastObject] stringByRemovingPercentEncoding];
            }
        }
    }
    return nil;
}

You can do that easy :

- (NSMutableDictionary *) getUrlParameters:(NSURL *) url
{
    NSMutableDictionary *params = [[NSMutableDictionary alloc] init];
    NSString *tmpKey = [url query];
    for (NSString *param in [[url query] componentsSeparatedByString:@"="])
    {
        if ([tmpKey rangeOfString:param].location == NSNotFound)
        {
            [params setValue:param forKey:tmpKey];
            tmpKey = nil;
        }
        tmpKey = param;
    }
    [tmpKey release];

    return params;
}

It return Dictionary like it : Key = value

I edited Dimitris' code slightly for better memory management and efficiency. Also, it works in ARC.

URLParser.h

@interface URLParser : NSObject

- (void)setURLString:(NSString *)url;
- (NSString *)valueForVariable:(NSString *)varName;

@end

URLParser.m

#import "URLParser.h"

@implementation URLParser {
    NSMutableDictionary *_variablesDict;
}

- (void)setURLString:(NSString *)url {
    [_variablesDict removeAllObjects];

    NSString *string = url;
    NSScanner *scanner = [NSScanner scannerWithString:string];
    [scanner setCharactersToBeSkipped:[NSCharacterSet characterSetWithCharactersInString:@"&?"]];
    NSString *tempString;

    [scanner scanUpToString:@"?" intoString:nil];       //ignore the beginning of the string and skip to the vars
    while ([scanner scanUpToString:@"&" intoString:&tempString]) {
        NSString *dataString = [tempString copy];
        NSArray *sepStrings = [dataString componentsSeparatedByString:@"="];
        if ([sepStrings count] == 2) {
            [_variablesDict setValue:sepStrings[1] forKeyPath:sepStrings[0]];
        }
    }
}

- (id)init
{
    self = [super init];
    if (self) {
        _variablesDict = [[NSMutableDictionary alloc] init];
    }
    return self;
}

- (NSString *)valueForVariable:(NSString *)varName {
    NSString *val = [_variablesDict valueForKeyPath:varName];
    return val;
    return nil;
}

-(NSString *)description {
    return [NSString stringWithFormat:@"Current Variables: %@", _variablesDict];
}

@end

Quickest is:

NSString* x = [url valueForQueryParameterKey:@"x"];