Adding admob to base appdelegate so it can be persistent thoughout all views

I want to add admob to the base app delegate so that I can have a persistent ad that will show though out all views instead of refreshing the every time i change the view Controllers. "bannerView_.rootViewController = self;" is the problem i do not know how to get this to work across all the view controllers. How can I from the base app delegate be able to get the current viewcontroller displayed on the app.

This is the code that i have currently in app delegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{


    // Create a view of the standard size at the bottom of the screen.
    bannerView_ = [[GADBannerView alloc]
  开发者_开发技巧                 initWithFrame:CGRectMake(0.0,
                                            self.window.frame.size.height -
                                            GAD_SIZE_320x50.height,
                                            GAD_SIZE_320x50.width,
                                            GAD_SIZE_320x50.height)];

    // Specify the ad's "unit identifier." This is your AdMob Publisher ID.
    bannerView_.adUnitID = @"a14e0dssddb01d";

    // Let the runtime know which UIViewController to restore after taking
    // the user wherever the ad goes and add it to the view hierarchy.
    bannerView_.rootViewController = self;


    // Initiate a generic request to load it with an ad.
    [bannerView_ loadRequest:[GADRequest request]];


    //[self.window addSubview:navController.view];
     [self.window addSubview:bannerView_];
    [self.window makeKeyAndVisible];

    return YES;
}