How to intercept iPhone rotation

Question

in my app I got a Home with several buttons. Each button opens a separate view. In each view, if I put the device in landscape a help view is shown. Everything works fine except that in whatever view I am, if I put the iPhone like to lay on a table (I don't know how to eplain better...) the app exites from that view and comes back to the first view, the Home. Here's my code:

- (void)viewDidLoad
{
[super viewDidLoad];
[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
[[NSNotificationCenter defaultCenter] addObserver:self 
selector:@selector(orientationChanged:)name:@"UIDeviceOrientationDidChangeNotification" 
object:nil];
[self performSelector:@selector (ritardo) withObject:nil afterDelay:5.0f];
}

-(void)orientationChanged:(NSNotification *)object{
UIDeviceOrientation deviceOrientation = [[object object] orientation];

if (deviceOrientation == UIInterfaceOrientationPortrait)
{
    [UIView beginAnimations:@"View Flip" context:nil];
    [UIView setAnimationDuration:0.5f];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
    self.view = self.portraitView;
}
else  if (deviceOrientation == UIInterfaceOrientationLandscapeLeft || deviceOrientation 
== UIInterfaceOrientationLandscapeRight)
{
    [UIView beginAnimations:@"View Flip" context:nil];
    [UIView setAnimationDuration:0.5f];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
    self.view = self.landscapeView;
}
[UIView commitAnimations];
[self dismissModalViewControllerAnimated:NO];
}

-(void) ritardo {
ruota.image = [UIImage imageNamed:@"RuotaPerAiuto.png"];    
}

- (void)viewDidUnload
{
[self setPortraitView:nil]; 
[self setLandscapeView:nil];
[self setRuota:nil];
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation: 
(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
} else {
    return YES;
}
}
@end

Hi hope you can help me

EDIT: I modified the -(void)orientationChanged:(NSNotification *)object{ in this way:

-(void)orientationChanged:(NSNotification *)object{
UIDeviceOrientation deviceOrientation = [[object object] orientation];
if (deviceOrientation == UIDeviceOrientationFaceUp)// || deviceOrientation == 
UIDeviceOrientationFaceDown) 
{
    return;
}
if (deviceOrientation == UIInterfaceOrientationPortrait || deviceOrientation == 
UIInterfaceOrientationPortraitUpsideDown)
{
    [UIView beginAnimations:@"View Flip" context:nil];
    [UIView setAnimationDuration:0.5f];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
    self.view = self.portraitView;
}
else 
if (deviceOrientation == UIInterfaceOrientationLandscapeLeft || deviceOrientation == 
UIInterfaceOrientationLandscapeRight)
{
    [UIView beginAnimations:@"View Flip" context:nil];
    [UIView setAnimationDuration:0.5f];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
    self.view = self.landscapeView;
}
[UIView commitAnimations];
[self dismissModalViewControllerAnimated:NO];
}

Now, if I'm in portrait and get the iPhone to faceUp position works good. But when I change position from faceUp to portrait it goes back to the home...

Answer 1

The problem is that UIDeviceOrientationDidChangeNotification will be fired independently from shouldAutorotateToInterfaceOrientation. And you don't handle the cases UIInterfaceOrientationPortraitUpsideDown, UIDeviceOrientationFaceUp and UIDeviceOrientationFaceDown in the method orientationChanged:. So when the device is rotated to one of these orientations, your code is equivalent to:

-(void)orientationChanged:(NSNotification *)object
{
    [UIView commitAnimations];
    [self dismissModalViewControllerAnimated:NO];
}

So you should remove the lines:

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

and put you code in the method willRotateToInterfaceOrientation:

- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation duration:(NSTimeInterval)duration
{
    [UIView beginAnimations:@"View Flip" context:nil];
    [UIView setAnimationDuration:0.5f];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
    if (UIInterfaceOrientationIsPortrait(interfaceOrientation)) {
        self.view = self.portraitView;
    } else {
        self.view = self.landscapeView;
    }
    [UIView commitAnimations];
    [self dismissModalViewControllerAnimated:NO];
}

Edit

If you want to keep orientationChanged, then modify it as follows:

-(void)orientationChanged:(NSNotification *)object{
    UIDeviceOrientation deviceOrientation = [[object object] orientation];
    if (deviceOrientation == UIInterfaceOrientationPortrait) {
        [UIView beginAnimations:@"View Flip" context:nil];
        [UIView setAnimationDuration:0.5f];
        [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
        self.view = self.portraitView;
        [UIView commitAnimations];
        [self dismissModalViewControllerAnimated:NO];
    } else  if (deviceOrientation == UIInterfaceOrientationLandscapeLeft || deviceOrientation == UIInterfaceOrientationLandscapeRight) {
        [UIView beginAnimations:@"View Flip" context:nil];
        [UIView setAnimationDuration:0.5f];
        [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
        self.view = self.landscapeView;
        [UIView commitAnimations];
        [self dismissModalViewControllerAnimated:NO];
    }
}