App shows white screen sometimes - iOS4

My app runs well on iOS4, except that sometimes it shows a whitescreen, especially after a long period of time not using the app (I guess that it may get deleted from the background, but I already tried), but then, if I close the app and reopen it again, everything works just fine. I don't know if there is any specific problem with this. It is a normal iphone app with tabs.

Here is the application:didFinishLaunchingWithOptions:,

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {


    gpsUpdate=0;
    NSLog(@"entro a didFinishLaunch");
    if (locationManager == nil ) {
    }

    if ([launchOptions objectForKey: UIApplicationLaunchOptionsLocationKey] != nil) {

            // register for local notification
    }
    else {
        iconBadNumber=0;
        [self checkConnection];
        [self copyDatabaseIfNeeded];
        iconBadNumber=0;
        self.alertsArray = [[NSMutableArray alloc] init];
        self.searchArray = [[NSMutableArray alloc] init];

        [Alertas getAllAlerts];

        [window addSubview:tabBarController.view];
    }       

    [tabBarController set开发者_StackOverflowDelegate:self];
    return YES;
}

you are adding subview as tabBarController.view for window in only one condition. Always inside the didFinishLaunchingWithOptions method you need to add some view as a subview to window otherwise it will show white screen as it is the default color of the window.