iOS back to root ViewController in the modal and navigation uiviewcontroller

I have a structure about navigation and many page have modal (popup) on the uiviewcontroller(UINavigationController).

When I disconnect the bluetooth, I need back to the root the viewcontroller.

So I set the dismiss and popToRoot in the disconnect method

 -(void) disconnect
 {
 ....
  [appDelegate.window.rootViewController dismissViewControllerAnimated:NO completion:nil];

  NSLog(@"appDelegate.window.rootViewController:%@",appDelegate.window.rootViewController.class);
 // show log appDelegate.window.rootViewController:UINavigationController

  [appDelegate.window.rootViewController.navigationController popToRootViewControllerAnimated:YES];
 ....
 }

But when I run the program and disconnect bluetooth,

In the case 1: modal the viewcontroller showing,

It will dismiss the modal viewcontroller, the dismiss was correct.

But there are not back to the root navigation controller after dismiss modal viewcontroller.

In the case2: just in the uinavigation controller page.

when I disconnect the bluetooth, there are not back to the root navigation controller.

How can I back to the navigation root page?where are my fails?

thank you very much.

// ------ answer -------

change code to

  [appDelegate.window.rootViewController dismissViewControllerAnimated:NO completion:nil];

     [self performSelector:@selector(gotoRoot) withObject:nil afterDelay:0.50];

 - (void) gotoRoot {

     UINavigationController *myNavCon = (UINavigationController*)appDelegate.window.rootViewController;

     [myNavCon popToRootViewControllerAnimated:YES];
 }

From the class you presented your modal view call dismiss of modal and then perform selector after some delay and then do the here is the sample code

- (void) dismissAndGoToRoot {
      [self dismissViewControllerAnimated:YES completion:nil];
      [self performSelector:@selector(gotoRoot) withObject:nil afterDelay:0.50];
}

- (void)gotoRoot {

    [self.navigationController popToRootViewControllerAnimated:NO];
}