title: screen not starting on iphone application
body: <p>I am starting an iPhone application, and I can't seem to get the main screen started. Here is my delegate.h file:</p>
  
  <pre><code>#import &lt;UIKit/UIKit.h&gt;
  
  @class MainViewController;
  
  @interface AppDelegate : UIResponder &lt;UIApplicationDelegate&gt;
  
  @property (strong, nonatomic) UIWindow *window;
  @property (retain, nonatomic) MainViewController *mainViewController;
  
  @end
  </code></pre>
  
  <p>and here is my implementation file(at least the beginning):</p>
  
  <pre><code>#import "AppDelegate.h"
  #import "MainViewController.h"
  
  @implementation AppDelegate
  
  @synthesize window = _window;
  @synthesize mainViewController = _mainViewController;
  
  
  - (void)dealloc
  {
      [_window release];
      [_mainViewController];
      [super dealloc];
  }
  
  - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
  {
  
  MainViewController *aViewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
  [self setMainViewController:aViewController];
  [aViewController release];
  
  self.window.rootViewController = self.mainViewController;
  
  [self.window makeKeyAndVisible];
  
  return YES;
  }
  </code></pre>
  
  <p>When I try to run the app, just a black screen appears, and even after waiting a long time, the screen won't show the contents of my MainViewController.xib file...</p>
  
  <p>Any ideas?</p>