Question

is there any difference when we use following two methods for orientation change in iOS.

1) Using NotificationCenter

[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(orientationChange) name:UIDeviceOrientationDidChangeNotification object:nil];

-(void) orientationChange
{
    UIDeviceOrientation orientation = [[UIDevice currentDevice] orientation];
    NSLog(@"Orientation =%d",orientation);
    NSLog(@"in Testtt");
}

2) ViewController Orientation delegate methods

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    if(UIInterfaceOrientationLandscapeRight == interfaceOrientation || UIInterfaceOrientationLandscapeLeft == interfaceOrientation)
        return YES;
    else 
        return NO;
}

Answer 1

In first case you will receive UIDeviceOrientation.[[UIDevice currentDevice] orientation] returns UIDeviceOrientation, device orientation. But note that UIDeviceOrientation is not always UIInterfaceOrientation. For example, when your device is on a plain table you can receive unexpected value (UIDeviceOrientationUnknown).

In shouldAutorotateToInterfaceOrientation method you can access UIInterfaceOrientation, current orientation of the interface.