如何防止当前模态的活动控制器？
我们有2个控制器：MainVC和ProfileVC。 从MainVC我们转到ProfileVC with profileButton press（导航栏上的左项）。
在Profile VC中，导航栏上有2个按钮：返回main（leftItem）并打开alertView（rightItem）。
所以有简单的KIF测试（导航栏上只有永久的左右点击）：
- (void)testProfileButtons { [tester waitForAnimationsToFinishWithTimeout:0.3]; while (true) { [tester tapScreenAtPoint:CGPointMake(20, 20)]; [tester waitForTimeInterval:0.1]; [tester tapScreenAtPoint:CGPointMake(380, 20)]; [tester waitForTimeInterval:0.1]; [tester tapScreenAtPoint:CGPointMake(20, 20)]; [tester waitForTimeInterval:0.1]; } }
它崩溃了应用程序错误：
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present modally an active controller .'
*** First throw call stack: ( 0 CoreFoundation 0x0000000110944c65 __exceptionPreprocess + 165 1 libobjc.A.dylib 0x00000001105dabb7 objc_exception_throw + 45 2 UIKit 0x000000010f44b80d -[UIViewController _presentViewController:withAnimationController:completion:] + 3238 3 UIKit 0x000000010f44d6c1 __62-[UIViewController presentViewController:animated:completion:]_block_invoke + 132 4 UIKit 0x000000010fa5e5ae -[_UIViewControllerTransitionCoordinator _applyBlocks:releaseBlocks:] + 217 5 UIKit 0x000000010fa5b8e5 -[_UIViewControllerTransitionContext _runAlongsideCompletions] + 123 6 UIKit 0x000000010fa5b670 -[_UIViewControllerTransitionContext completeTransition:] + 126 7 UIKit 0x000000010f2fe8a6 __53-[_UINavigationParallaxTransition animateTransition:]_block_invoke93 + 687 8 UIKit 0x000000010f387193 -[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:] + 326 9 UIKit 0x000000010f36e0f6 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 209 10 UIKit 0x000000010f36e42c -[UIViewAnimationState animationDidStop:finished:] + 76 11 UIKit 0x000000011daf3fdf -[UIViewAnimationStateAccessibility animationDidStop:finished:] + 48 12 QuartzCore 0x000000010f03e892 _ZN2CA5Layer23run_animation_callbacksEPv + 308 13 libdispatch.dylib 0x0000000111c67964 _dispatch_client_callout + 8 14 libdispatch.dylib 0x0000000111c52a59 _dispatch_main_queue_callback_4CF + 704 15 CoreFoundation 0x00000001108ac1f9 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9 16 CoreFoundation 0x000000011086ddcb __CFRunLoopRun + 2043 17 CoreFoundation 0x000000011086d366 CFRunLoopRunSpecific + 470 18 TurboChat UI Tests 0x000000011b73ef69 -[KIFTestActor tryRunningBlock:complete:timeout:error:] + 425 19 TurboChat UI Tests 0x000000011b73f179 -[KIFTestActor runBlock:complete:timeout:] + 137 20 TurboChat UI Tests 0x000000011b73f304 -[KIFTestActor runBlock:timeout:] + 84 21 TurboChat UI Tests 0x000000011b73f73e -[KIFTestActor waitForTimeInterval:] + 174 22 TurboChat UI Tests 0x000000011b73c2ad -[TCProfileButtonsTest testProfileButtons] + 909 23 CoreFoundation 0x000000011083adec __invoking___ + 140 24 CoreFoundation 0x000000011083ac42 -[NSInvocation invoke] + 290 25 XCTest 0x000000011b79217a -[XCTestCase invokeTest] + 253 26 XCTest 0x000000011b792379 -[XCTestCase performTest:] + 150 27 XCTest 0x000000011b79bc35 -[XCTest run] + 260 28 XCTest 0x000000011b79108b -[XCTestSuite performTest:] + 379 29 XCTest 0x000000011b79bc35 -[XCTest run] + 260 30 XCTest 0x000000011b79108b -[XCTestSuite performTest:] + 379 31 XCTest 0x000000011b79bc35 -[XCTest run] + 260 32 XCTest 0x000000011b79108b -[XCTestSuite performTest:] + 379 33 XCTest 0x000000011b79bc35 -[XCTest run] + 260 34 XCTest 0x000000011b78e129 __25-[XCTestDriver _runSuite]_block_invoke + 56 35 XCTest 0x000000011b798edd -[XCTestObservationCenter _observeTestExecutionForBlock:] + 162 36 XCTest 0x000000011b78e060 -[XCTestDriver _runSuite] + 269 37 XCTest 0x000000011b78ea8d -[XCTestDriver _checkForTestManager] + 234 38 XCTest 0x000000011b79eb20 +[XCTestProbe runTests:] + 182 39 Foundation 0x000000010e5f21e5 __NSFireDelayedPerform + 387 40 CoreFoundation 0x00000001108ac174 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20 41 CoreFoundation 0x00000001108abd35 __CFRunLoopDoTimer + 1045 42 CoreFoundation 0x000000011086dd3d __CFRunLoopRun + 1901 43 CoreFoundation 0x000000011086d366 CFRunLoopRunSpecific + 470 44 GraphicsServices 0x00000001123a8a3e GSEventRunModal + 161 45 UIKit 0x000000010f30e8c0 UIApplicationMain + 1282 46 TurboChat 0x000000010cd1e75f main + 111 47 libdyld.dylib 0x0000000111c97145 start + 1 )
在真实设备上测试时我也会得到这个：
Presenting view controllers on detached view controllers is discouraged .
并获得alertView出现在MainVC而不是ProfileVC下面的黑色屏幕。
这就是我们如何在ProfileVC中呈现警报：
- (IBAction)menuButtonPressed:(id)sender { [self.navigationController presentViewController:self.menuAlert animated:YES completion:nil]; }
AlertView：
self.menuAlert = [UIAlertController alertControllerWithTitle:[NSString stringWithFormat:@"%@?", NSLocalizedString(@"PROFILE_BTN_MENU", nil)] message:nil preferredStyle:UIAlertControllerStyleActionSheet];
有什么建议么？
我想你需要首先解除LAST viewcontroller，然后回到现有的模态segue，viewcontroller是活动的，所以它崩溃了：
在使用mainVC调用segue之后使用此function或者您希望返回的内容：
[self dismissViewControllerAnimated:NO completion:nil]
要么
[[self presentingViewController] dismissViewControllerAnimated:NO completion:nil]
或者使用push segue，它会自动添加一个自动添加function的后退按钮
我找到了一种解决方案
- (IBAction)menuButtonPressed:(id)sender { [self.parentViewController presentViewController:self.menuAlert animated:YES completion:nil]; }
警报视图有时会出现在menuVC上，但它不会使应用程序崩溃并正常工作。 在那里找到答案： 警告： – 不建议在分离的视图控制器上显示视图控制器
其他开发者可能还有另一种情况：
在按钮触发连接后是否显示目标ViewController？ 如果您拥有所述ViewController的共享实例，则用户可能会点击两次，进行两次连接并打开两次相同的ViewController。
通过这样做来防止它：
var didSuccess = false func success(result: LoginModel.Result) { if didSuccess { return } didSuccess = true Answers.logCustomEvent(withName: "Login") Session.set(token: result.token) present(MainTabBarController.sharedInstance, animated: true, completion: nil) }
或者在连接期间禁用该按钮。
防止这种exception。 只需忽略当前显示的ViewController就可以返回到您正在解雇的ViewController的调用者：
self.dismiss(animated: true, completion: nil)