Question

好吧，我没有开始使用Objective C和Xcode - 这是我第二次来这里寻求帮助的一个简单项目 - 令人尴尬！

我的主（Squad）视图控制器加载一个细节（Pilot）视图控制器，后者又加载一个带模态segue的第三个视图控制器（SelectNewPilot）。这很好用。如果按SelectNewPilot（模态）视图上的取消按钮，它将展开到Pilot（详细信息）视图控制器。在Pilot视图控制器中，我有以下代码：

- (IBAction)unwindToList:(UIStoryboardSegue *)segue
{
    UIViewController *source = [segue sourceViewController];
    if([source isKindOfClass:[Mz0SelectNewPilotViewController class]])
    {
        if ([(Mz0SelectNewPilotViewController *)source pilot] == nil)
        {
            NSLog(@"We cancelled selecting a new pilot");
            [self performSegueWithIdentifier:@"Unwind" sender:self];
        }
        else
        {
            NSLog(@"We selected %@", [[(Mz0SelectNewPilotViewController *)source pilot] name]);
        }
    }
}

因此，如果SelectNewPilot（模态）控制器中没有选择任何内容（即它被取消），则Pilot控制器会自动进一步退回到Squad（主）控制器。这会产生以下错误：

2014-03-13 00:45:07.578 Squad Builder[3149:70b] *** Assertion failure in -[UINavigationController popToViewController:transition:], /SourceCache/UIKit_Sim/UIKit-2935.120.3/UINavigationController.m:4886
2014-03-13 00:45:07.581 Squad Builder[3149:70b] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Tried to pop to a view controller that doesn't exist.'
*** First throw call stack:
(
    0   CoreFoundation                      0x01b629e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x018e28e5 objc_exception_throw + 44
    2   CoreFoundation                      0x01b62848 +[NSException raise:format:arguments:] + 136
    3   Foundation                          0x014c20de -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 116
    4   UIKit                               0x006edbe0 -[UINavigationController popToViewController:transition:] + 302
    5   UIKit                               0x006edaad -[UINavigationController popToViewController:animated:] + 56
    6   UIKit                               0x006e633f __90-[UINavigationController segueForUnwindingToViewController:fromViewController:identifier:]_block_invoke + 142
    7   UIKit                               0x00b197ac -[UIStoryboardSegue perform] + 35
    8   UIKit                               0x00c7d623 -[UIStoryboardUnwindSegueTemplate _perform:] + 554
    9   UIKit                               0x00b090b7 -[UIStoryboardSegueTemplate perform:] + 115
    10  libobjc.A.dylib                     0x018f4880 -[NSObject performSelector:withObject:withObject:] + 77
    11  UIKit                               0x005a67f9 -[UIApplication sendAction:to:from:forEvent:] + 108
    12  UIKit                               0x008938bf -[UIBarButtonItem(UIInternal) _sendAction:withEvent:] + 139
    13  libobjc.A.dylib                     0x018f4880 -[NSObject performSelector:withObject:withObject:] + 77
    14  UIKit                               0x005a67f9 -[UIApplication sendAction:to:from:forEvent:] + 108
    15  UIKit                               0x005a6785 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 61
    16  UIKit                               0x006a7fe1 -[UIControl sendAction:to:forEvent:] + 66
    17  UIKit                               0x006a83d6 -[UIControl _sendActionsForEvents:withEvent:] + 577
    18  UIKit                               0x006a7653 -[UIControl touchesEnded:withEvent:] + 641
    19  UIKit                               0x005e621d -[UIWindow _sendTouchesForEvent:] + 852
    20  UIKit                               0x005e6e11 -[UIWindow sendEvent:] + 1117
    21  UIKit                               0x005b8a32 -[UIApplication sendEvent:] + 242
    22  UIKit                               0x005a2793 _UIApplicationHandleEventQueue + 11455
    23  CoreFoundation                      0x01aebf7f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
    24  CoreFoundation                      0x01aeb90b __CFRunLoopDoSources0 + 235
    25  CoreFoundation                      0x01b089ae __CFRunLoopRun + 910
    26  CoreFoundation                      0x01b081d3 CFRunLoopRunSpecific + 467
    27  CoreFoundation                      0x01b07feb CFRunLoopRunInMode + 123
    28  GraphicsServices                    0x03a175ee GSEventRunModal + 192
    29  GraphicsServices                    0x03a1742b GSEventRun + 104
    30  UIKit                               0x005a53db UIApplicationMain + 1225
    31  Squad Builder                       0x0000a6bd main + 141
    32  libdyld.dylib                       0x021ad701 start + 1
)

如果我注释掉这条线 [self performSegueWithIdentifier：@“Unwind”sender：self]; 然后它工作正常，你只需按下Pilot控制器上的取消就可以回到Squad控制器。我的问题是当你使用按钮来触发它时，为什么放松segue（从Pilot到Squad）工作，但是当以编程方式调用时（它是相同的展开segue，我只是将一个标识符应用于取消按钮使用的那个）？

小队控制器中的unwindToList方法完成，所以我不确定是什么被调用导致错误。什么使segue试图弹出一些东西？这是故事板中的某个地方吗？

Squad控制器的unwindToList方法如下（两个NSLog输出都出现在错误之前）：

- (IBAction)unwindToList:(UIStoryboardSegue *)segue
{
    NSLog(@"Unwound to Squad");
    Mz0PilotViewController *source = [segue sourceViewController];
    Mz0Card *pilot = [source pilot];
    if ([pilot isKindOfClass:[Mz0Card class]])
    {
        NSLog(@"Adding new pilot: %@", [pilot name]);
        if(![_testData containsObject:pilot])
        {
            [_testData addObject:pilot];
            [self.tableView reloadData];
        }
    }
    NSLog(@"Finished unwinding to Squad");
}

更新：在开始打印输出（然后是最终错误）之前，我刚发现另一个错误：

Unbalanced calls to begin/end appearance transitions for <Mz0SquadViewController: 0x8dc8720>

这是因为它试图放松太快吗？有没有办法告诉它不要从Pilot到Squad放松，直到第一次放松（从SelectNewPilot到Pilot）完成？

unwind segue使用按钮但不能以编程方式工作 - 为什么？

0 个答案: