崩溃呈现模态视图控制器

Question

我有这个崩溃。它与其他线程类似，但又不一样。 我想首先向用户显示一个模式视图控制器，然后转到特定的视图控制器。按照提示，我在 - (void) viewDidAppear:(BOOL)animated 上执行此操作，并按照我看到的建议应用延迟。

 - (void) viewDidAppear:(BOOL)animated 
    {
      [super viewDidAppear:animated];
       [self performSelector:@selector(presentMyModal) withObject:nil afterDelay:1];
    }



     - (void) presentModal{
    ModalViewController *modal = [[[ModalViewController alloc] init] autorelease];
    [self presentModalViewController:modal animated:YES];   
   }

然后，随机地崩溃了。我在控制台中收到此消息：

<Warning>: *** Assertion failure in -[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:], /SourceCache/UIKit/UIKit-1447.6.4/UIWindowController.m:186
Thu Feb  3 10:00:44 unknown MyApp[1830] <Error>: *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Attempting to begin a modal transition from <UINavigationController: 0x454260> to <ModalViewController: 0x47af00> while a transition is already in progress. Wait for viewDidAppear/viewDidDisappear to know the current transition has completed'
    *** Call stack at first throw:
    (
        0   CoreFoundation                      0x3759dc7b __exceptionPreprocess + 114
        1   libobjc.A.dylib                     0x32d9bee8 objc_exception_throw + 40
        2   CoreFoundation                      0x3759dac3 +[NSException raise:format:arguments:] + 70
        3   Foundation                          0x351a3e73 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 62
        4   UIKit                               0x359e92a8 -[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:] + 208
        5   UIKit                               0x359e8c98 -[UIViewController presentModalViewController:withTransition:] + 2792
        6   UIKit                               0x35a7b51c -[UIViewController _tryRecursivelyPresentModalViewController:withTransition:] + 116
        7   UIKit                               0x359e84c0 -[UIViewController presentModalViewController:withTransition:] + 784
        8   UIKit                               0x359e8060 -[UIViewController presentModalViewController:animated:] + 96
        9   MyApp                         0x0005d57f -[MyAppViewController presentMyModal] + 58
        10  Foundation                          0x351724db __NSFireDelayedPerform + 366
        11  CoreFoundation                      0x37552305 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 16
        12  CoreFoundation                      0x37551cd9 __CFRunLoopDoTimer + 988
        13  CoreFoundation                      0x37521a91 __CFRunLoopRun + 1184
        14  CoreFoundation                      0x3752150b CFRunLoopRunSpecific + 226
        15  CoreFoundation                      0x37521419 CFRunLoopRunInMode + 60
        16  GraphicsServices                    0x33e76d24 GSEventRunModal + 196
        17  UIKit                               0x3591d57c -[UIApplication _run] + 588
        18  UIKit                               0x3591a558 UIApplicationMain + 972
        19  MyApp                         0x0000e75f main + 50
        20  MyApp                         0x0000e6e8 start + 52

如您所见，我等待视图出现。这可能是操作系统错误吗？看起来它试图递归地呈现其他模式视图控制器，从而引发崩溃。 多谢。

Answer 1

除了我在评论中挑剔之外，我想我也可以帮助解决这个问题。我认为你需要在其他地方寻找罪魁祸首。我用这个代码片段创建了一个新项目和一个视图控制器：

#import "VC1.h"


@implementation VC1

- (void) viewDidAppear:(BOOL)animated {
  [super viewDidAppear:animated];
  [self performSelector:@selector(presentModal) withObject:nil afterDelay:1.0];
}

- (void)presentModal {
  static int colorChooser = 0;
  VC1 *vc1 = [[[VC1 alloc] init] autorelease];
  switch (colorChooser%2) {
    case 0:
      vc1.view.backgroundColor = [UIColor whiteColor];
      break;
    default:
      vc1.view.backgroundColor = [UIColor blackColor];
      break;
  }
  colorChooser++;
  [self presentModalViewController:vc1 animated:YES];
}

@end

并且在被推送到导航控制器上后它可以完美地工作。它在黑白视图之间递归交替，并在 sim 和 3G 设备上进行了测试。

也许由于某些通知或其他异步方式，您正在执行其他一些视图转换？无论哪种方式，您都需要共享更多代码，以便任何人都知道问题出在哪里。

Answer 2

我们首选的解决方案是使用 -[UIViewController PresentViewController:animated:completion:] 并在完成块中执行下一个操作（例如呈现另一个 VC）。

例如：

[self presentViewController:yourViewController animated:YES completion:^{
    [yourViewController presentMyModal];
}];

该方法是在iOS 5.0中引入的。