ios - How to use URLDecode? - iphone

Question

I'm trying to get access token,I'm following this link http://www.stevesaxon.me/posts/2011/window-external-notify-in-ios-uiwebview/ to get that,but I'm getting some problem when decode URL.Please go through that link.
- (NSDictionary*)parsePairs:(NSString*)urlStr
{
NSRange r = [urlStr rangeOfString:#"="];
if(r.length == 0)
{
return nil;
}
//Here Program received signal stopped
NSString* token = [[urlStr substringFromIndex:r.location + 1 ] URLDecode];
NSCharacterSet* objectMarkers;
objectMarkers = [NSCharacterSet characterSetWithCharactersInString:#"{}"];
token = [token stringByTrimmingCharactersInSet:objectMarkers];
NSError* regexError;
NSMutableDictionary* pairs = [NSMutableDictionary dictionaryWithCapacity:10];
NSRegularExpression* regex;
regex = [NSRegularExpression regularExpressionWithPattern:#"\"([^\"]*)\":\"([^\"]*)\""
options:0
error:&regexError];
NSArray* matches = [regex matchesInString:token
options:0
range:NSMakeRange(0, token.length)];
for(NSTextCheckingResult* result in matches)
{
for(int n = 1; n < [result numberOfRanges]; n += 2)
{
NSRange r = [result rangeAtIndex:n];
if(r.length > 0)
{
NSString* name = [token substringWithRange:r];
r = [result rangeAtIndex:n + 1];
if(r.length > 0)
{
NSString* value = [token substringWithRange:r];
[pairs setObject:value forKey:name];
}
}
}
}
regex = [NSRegularExpression regularExpressionWithPattern:#"\"([^\"]*)\":([0-9]*)"
options:0
error:&regexError];
matches = [regex matchesInString:token
options:0
range:NSMakeRange(0, token.length)];
for(NSTextCheckingResult* result in matches)
{
for(int n = 1; n < [result numberOfRanges]; n += 2)
{
NSRange r = [result rangeAtIndex:n];
if(r.length > 0)
{
NSString* name = [token substringWithRange:r];
r = [result rangeAtIndex:n + 1];
if(r.length > 0)
{
NSString* value = [token substringWithRange:r];
NSNumber* number = [NSNumber numberWithInt:[value intValue]];
[pairs setObject:number forKey:name];
}
}
}
}
return pairs;
}
Any ideas? Thanks in advance.