How can i implement iAd using singleton class - objective-c

Question

I want to implement iAd in my viewController so that i created the singleton class for iAd here the code that i used but it doesnt display iAd in my viewController.
adWhirlSingleton.h
#import <Foundation/Foundation.h>
#import "iAd/ADBannerView.h"
#interface adWhirlSingleton : NSObject <ADBannerViewDelegate> {
ADBannerView *adView;
UIViewController *displayVC;
}
#property (strong, nonatomic) ADBannerView *adView;
#property (strong, nonatomic) UIViewController *displayVC;
+(id)sharedAdSingleton;
-(void)adjustAdSize:(CGFloat)x:(CGFloat)y;
#end
adWhirlSingleton.m
#import "adWhirlSingleton.h"
#implementation adWhirlSingleton
static adWhirlSingleton* _sharedAdSingleton = nil;
#synthesize adView, displayVC;
+(id)sharedAdSingleton
{
#synchronized(self)
{
if(!_sharedAdSingleton)
_sharedAdSingleton = [[self alloc] init];
return _sharedAdSingleton;
}
return nil;
}
+(id)alloc
{
#synchronized([adWhirlSingleton class])
{
NSAssert(_sharedAdSingleton == nil, #"Attempted to allocate a second instance of a singleton.");
_sharedAdSingleton = [super alloc];
return _sharedAdSingleton;
}
return nil;
}
-(id)init
{
self = [super init];
if (self != nil) {
// initialize stuff here
self.adView.delegate=self;
}
return self;
}
-(void)dealloc
{
displayVC = nil;
if (adView) {
[adView removeFromSuperview]; //Remove ad view from superview
[adView setDelegate:nil];
adView = nil;
}
[super dealloc];
}
-(void)adjustAdSize:(CGFloat)x :(CGFloat)y
{
[UIView beginAnimations:#"AdResize" context:nil];
[UIView setAnimationDuration:0.7];
adView.frame = CGRectMake(x, y, 320, 50);
[UIView commitAnimations];
}
-(BOOL)adWhirlTestMode
{
return YES;
}
-(NSString *)adWhirlApplicationKey
{
return #"xxxxxxxxxxxxx";
}
-(UIViewController *)viewControllerForPresentingModalView
{
return displayVC;
}
-(void)bannerViewDidLoadAd:(ADBannerView *)banner {
[self adjustAdSize:0 :410];
}
#end
myViewController.m
#import "adWhirlSingleton.h"
-(void)viewWillAppear:(BOOL)animated {
adWhirlSingleton *adWhirlSingle = [adWhirlSingleton sharedAdSingleton];
adWhirlSingle.displayVC = self;
[adWhirlSingle adjustAdSize:0 :self.view.frame.size.height -50];
[self.view addSubview:adWhirlSingle.adView];
[self.view bringSubviewToFront:adWhirlSingle.adView];
NSLog(#"Ad Banner View");
}
This is how i implemented the singleton class for iAd when i excute this i didnt get iAd displayed over my ViewController.
If anyone know how to implement this please help me to get out of this issue. Thanks in Advance.