Question

i use presentModalViewController to show some controller.

A controller://it will show controller of B and receive a message ,when it receive the Message,i want to kown the B is it show or not?

-(void)viewDidLoad{

     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(recvPushMessage:) name:RECV_PUSH_MESSAGE_NOTIFY object:nil];

}
-(void)buttonAction(id)sender{
     B* b = [B alloc] init];
     UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:(UIViewController*)b];
     [self presentModalViewController:navigationController animated:YES];
     //release 
}
-(void)recvPushMessage{
   //i want to kown B is it show or not
   if(b is showing){
      //do something
   }
   else{
      //do something for A
   }

}

B controller://when B was show ,i do not want call recvPushMessage in A.

 -(void)viewDidLoad{

     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(recvPushMessage:) name:RECV_PUSH_MESSAGE_NOTIFY object:nil];

}
-(void)recvPushMessage{

   //do something for B
}

Answer 1

Check if this is what you are looking for,

-(void)recvPushMessage{

   if (self.presentedViewController) { //check if you have this model view controller
      //do something
   }
   else{
      //do something for A
   }
}

For version < iOS 5.0, you can use self.modalViewController.

Update:
For your second question, you can get the topViewController of navigation controller and compare it with C. You can use something like [self.modalViewController topViewController] to check if it is C and then proceed.

For eg:-

if ([[(UINavigationController *)self.modalViewController topViewController] isKindOfClass:[C class]])