在iPhone中向其添加子視圖時如何保留超級視圖？

Question

我有一個應用程序，其中有一個視圖控制器，它是一個appdelegate實例。我將該視圖添加到self.navigationcontrollers視圖中，以便將其放置在導航欄上方。

if(appDelegate.viewcontroller==nil)
    {

        appDelegate.viewcontroller = [[ViewController alloc] init];
        [self.navigationController.view addSubview:appDelegate.viewcontroller.view];
        NSLog(@"My view frame: %@", NSStringFromCGRect(appDelegate.viewcontroller.view.frame));

        appDelegate.viewcontroller.view.tag=7;


        appDelegate.viewcontroller.view.frame =CGRectMake(0,480,300,460);
        [UIView animateWithDuration:.50 
                         animations:^{
       appDelegate.viewcontroller.view.frame =CGRectMake(0,30,300,440);
                         }];
        [appDelegate.viewcontroller viewWillAppear:YES];

    }
    else
    { 
        NSLog(@"My view frame: %@", NSStringFromCGRect(appDelegate.viewcontroller.view.frame));
        appDelegate.viewcontroller.view.frame=CGRectMake(0, 30,300, 440); 



        [self.navigationController.view addSubview:appDelegate.viewcontroller.view];


        appDelegate.viewcontroller.view.frame =CGRectMake(0,480,300,460);
        [UIView animateWithDuration:.50 
                         animations:^{
                             appDelegate.viewcontroller.view.frame =CGRectMake(0,30,300,440);
                         }];
       [appDelegate.viewcontroller viewWillAppear:YES];

    }

...Now i am adding another viewcontrollers view in to this view by

contactphoneForAddfriend= [[EventsViewController alloc]initWithNibName:@"EventsViewController" bundle:nil];
    contactphoneForAddfriend.orgarray=self.eventsArray;


    [UIView beginAnimations:@"View Flip" context:nil];
    [UIView setAnimationDuration:0.80];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];

    [UIView setAnimationTransition:
     UIViewAnimationTransitionFlipFromRight
                           forView:self.view cache:NO];


     [self.view addSubview:contactphoneForAddfriend.view];
    [UIView commitAnimations];  

當我進入應用程序的后台時，然后從該視圖控制器中...那個appdelegate viewcontroller顯示為nil。這是怎么發生的呢？畢竟它是一個appdelegate變量。當我刪除他添加的視圖然后去背景在那里。有人可以指出我要去哪里了嗎？

Answer 1

檢查您的代碼，發現viewController不是nil。通過在此方法中應用一些代碼來檢查自己

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    if (self.viewController==nil) {
        NSLog(@"ViewController is nil");
    }else{
        NSLog(@"ViewController Has value %@",NSStringFromClass([self.viewController class]));
    }
}