Basic loading image fading in and out using NSTimer and UIImageView / UIImage.

gistfile1.m

- (void)viewDidLoad
{
    
    [super viewDidLoad];

	// Create a container UIView - actually, this part might not be needed at all!.
    	// Establish this view with a 150x150pt frame, to fit our custom image.
    	// Note that it's in the top-left for the moment, don't worry about that for now.
	UIView *loader = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 150, 150)];
	
	// Load your image data using the +imageNamed method.
	UIImage *loaderImage = [UIImage imageNamed:@"Loading.png"];
	
	// Use the imageview to populate a UIImageView
	UIImageView *loaderImageView = [[UIImageView alloc] initWithImage:loaderImage];

	// Add the UIImageView as a subview of the containing UIView.
	[loader addSubview:loaderImageView];
    
	// Add the loader container view to our main UIViewControllers view
	[self.view addSubview:loader];
    
	// Start the initial animation - the name here doesn't matter for now.
	[UIImageView beginAnimations:@"FadeInOut" context:nil];
	
	// Make it last one second.
	[UIImageView setAnimationDuration:1.0f];
	
	// Add a quick ease-in-out curve.
	[UIImageView setAnimationCurve:UIViewAnimationCurveEaseInOut];
	
	// Now set the property we wanna animate, this being the alpha.
	loaderImageView.alpha = 0.0f;

	// Commit animations, this runs them.
	[UIImageView commitAnimations];
    
	// Now, we wanna keep animating this thing until the sun goes down, so set up a timer
	[NSTimer scheduledTimerWithTimeInterval:1.0 // How often to send a message asking what to do.
                                 target:self // Sends a message to this class at the interval above.
                               selector:@selector(timerHitInterval:) // The method we define below to receive the message
                                   userInfo:loaderImageView // pass our loaderImageView as userInfo so we can adjust it
                                    repeats:YES]; // Tell it to repeat after the first one
}

// Now define this method that will receive the message from the NSTimer instance every second.
- (void)timerHitInterval:(NSTimer*)timer
{
    // Assign our loaderView reference to a variable for compiler sanity.
    UIImageView *loaderView = timer.userInfo;
    
	// Declare this here - we're gonna change it dynamically.
    CGFloat newLoaderAlpha;
    
    if (loaderView.alpha == 0) { 
        newLoaderAlpha = 1.0; // If the opacity is at 0, send it to 1.
    } else {
        newLoaderAlpha = 0.0; // Vice versa.
    }

	// Perform the animations as in ViewDidLoad.
    
    [UIImageView beginAnimations:@"FadeInOut" context:nil];
    [UIImageView setAnimationDuration:1.0f];
    [UIImageView setAnimationCurve:UIViewAnimationCurveEaseInOut];
    loaderView.alpha = newLoaderAlpha;
    [UIImageView commitAnimations];
}