iphone - 对 UITabBarController 的开始/结束外观转换的调用不平衡

Question

我有一个 UITabBarController，在初始运行时，我想覆盖一个登录 View Controller ，但收到错误。

Unbalanced calls to begin/end appearance transitions for < UITabBarController: 0x863ae00 >.

下面是代码。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];

    // Override point for customization after application launch.

    UIViewController *lessonVC = [[[LessonViewController alloc] initWithNibName:@"LessonViewController" bundle:nil] autorelease];

    UIViewController *programVC = [[[ProgramViewController alloc] initWithNibName:@"ProgramViewController" bundle:nil] autorelease];

    UIViewController *flashcardVC = [[[FlashCardViewController alloc] initWithNibName:@"FlashCardViewController" bundle:nil] autorelease];

    UIViewController *moreVC = [[[MoreViewController alloc] initWithNibName:@"MoreViewController" bundle:nil] autorelease];

    UINavigationController *lessonNVC = [[[UINavigationController alloc] initWithRootViewController:lessonVC] autorelease];

    UINavigationController *programNVC = [[[UINavigationController alloc] initWithRootViewController:programVC] autorelease];

    UINavigationController *flashcardNVC = [[[UINavigationController alloc] initWithRootViewController:flashcardVC] autorelease];

    UINavigationController *moreNVC = [[[UINavigationController alloc] initWithRootViewController:moreVC] autorelease];

    self.tabBarController = [[[UITabBarController alloc] init/*WithNibName:nil bundle:nil*/] autorelease];
    self.tabBarController.viewControllers = [NSArray arrayWithObjects:lessonNVC, programNVC, flashcardNVC, moreNVC, nil];
    self.tabBarController.selectedIndex = 0;
    self.window.rootViewController = self.tabBarController;

    [self.window makeKeyAndVisible];

    if (![[ZYHttpRequest sharedRequest] userID]) 
    {
        // should register or login firstly
        LoginViewController *loginVC = [[LoginViewController alloc] initWithNibName:@"LoginViewController"
                                                                             bundle:nil];
        loginVC.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
        [self.tabBarController presentModalViewController:loginVC animated:YES];
        ZY_SAFE_RELEASE(loginVC);
    }

    return YES;
}

谁能帮帮我？提前致谢!

Answer 1

您需要等待下一次运行循环才能呈现模态视图 Controller 。我最终使用了一个 block (为了让事情变得更简单)来安排下一个运行循环的演示:

更新:
正如下面 Mark Amery 提到的，只需一个简单的 dispatch_async 即可工作，不需要计时器:

dispatch_async(dispatch_get_main_queue(), ^(void){     
  [self.container presentModalViewController:nc animated:YES]; 
});

<小时/>

/* Present next run loop. Prevents "unbalanced VC display" warnings. */
double delayInSeconds = 0.1;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    [self.container presentModalViewController:nc animated:YES];
});