How to add image over whole screen

Question

I am trying to put overlay image over whole iPhone screen (over navigation and tabbar also) from viewDidLoad but nothing happens.

self.imageView = [[UIImageView alloc]
                              initWithImage:[UIImage imageNamed:@"overlayimage.png"]];
UIWindow* window = [[UIApplication sharedApplication] keyWindow];
    [window.rootViewController.view addSubview: imageView];

UITapGestureRecognizer * recognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTap:)];
    recognizer.delegate = self;
    [imageView addGestureRecognizer:recognizer];
    imageView.userInteractionEnabled =  YES;
    self.imageView = imageView;

This is the result that I am trying to get:

Answer 1

Since UIWindow is a subclass of UIView, you can also add subviews to the key window.
These subviews will appear above any view controller.

UIWindow *keyWindow = [[[UIApplication sharedApplication] delegate] window];
[keyWindow addSubview:imageView];