SwiftUI 查看添加@Environment(\.presentationMode) crash.sheet() 演示

Question

我有視圖 uses.sheet() 以模態方式呈現一些我想在關閉此工作表時關閉 ParentView 的 ChildView。 所以有 onDismiss 回調。 但是，當我添加

@Environment(\.presentationMode) var presentationMode

然后提交工作表它會因此類錯誤而崩潰

libc++abi: terminating with uncaught exception of type NSException *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present modally a view controller < TtGC7SwiftUI29PresentationHostingControllerVS_7AnyView : 0x7ffc07175c60> that is already being presented by < TtGC7SwiftUI19UIHostingControllerGVS_15ModifiedContentVS_7AnyViewVS_12RootModifier _ ：0x7ffc04438c00>。' 以 NSException CoreSimulator 757.5 類型的未捕獲異常終止-設備：iPhone 12 Pro (DEE900D2-F542-496C-9000-14498B9AA407)-運行時：iOS 14.5 (18E182)-設備類型：iPhone 12 Pro

如果不使用此環境屬性，一切正常。 似乎工作表嘗試多次展示自己，然后此屬性可用。 但在其他屏幕（視圖）上一切正常。

*** First throw call stack:
(
    0   CoreFoundation                      0x0000000113b4ffba __exceptionPreprocess + 242
    1   libobjc.A.dylib                     0x00000001136cdff5 objc_exception_throw + 48
    2   UIKitCore                           0x0000000121df4f32 -[UIViewController _presentViewController:withAnimationController:completion:] + 6016
    3   UIKitCore                           0x0000000121df593c __63-[UIViewController _presentViewController:animated:completion:]_block_invoke + 98
    4   UIKitCore                           0x0000000121e1049c -[_UIViewControllerTransitionCoordinator _applyBlocks:releaseBlocks:] + 294
    5   UIKitCore                           0x0000000121e0c70e -[_UIViewControllerTransitionContext _runAlongsideCompletions] + 126
    6   UIKitCore                           0x0000000121e0c482 -[_UIViewControllerTransitionContext completeTransition:] + 106
    7   UIKitCore                           0x0000000122a2f3cc -[UITransitionView notifyDidCompleteTransition:] + 247
    8   UIKitCore                           0x0000000122a2f069 -[UITransitionView _didCompleteTransition:] + 1422
    9   UIKitCore                           0x0000000122a68e7a -[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:] + 779
    10  UIKitCore                           0x0000000122a39831 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 231
    11  UIKitCore                           0x0000000122a39dd6 -[UIViewAnimationState animationDidStop:finished:] + 263
    12  UIKitCore                           0x0000000122a39f57 -[UIViewAnimationState animationDidStop:finished:] + 648
    13  QuartzCore                          0x00000001122a8dc0 _ZN2CA5Layer23run_animation_callbacksEPv + 308
    14  libdispatch.dylib                   0x000000011ab8b74e _dispatch_client_callout + 8
    15  libdispatch.dylib                   0x000000011ab99b3f _dispatch_main_queue_callback_4CF + 1152
    16  CoreFoundation                      0x0000000113abd8f8 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
    17  CoreFoundation                      0x0000000113ab8169 __CFRunLoopRun + 2781
    18  CoreFoundation                      0x0000000113ab71a7 CFRunLoopRunSpecific + 567
    19  GraphicsServices                    0x0000000121151d85 GSEventRunModal + 139
    20  UIKitCore                           0x000000012251d4df -[UIApplication _run] + 912
    21  UIKitCore                           0x000000012252239c UIApplicationMain + 101
    22  SwiftUI                             0x0000000115b15c36 $s7SwiftUI17KitRendererCommon33_ACC2C5639A7D76F611E170E831FCA491LLys5NeverOyXlXpFAESpySpys4Int8VGSgGXEfU_ + 119
    23  SwiftUI                             0x0000000115b15bbd $s7SwiftUI6runAppys5NeverOxAA0D0RzlF + 143
    24  SwiftUI                             0x0000000115652384 $s7SwiftUI3AppPAAE4mainyyFZ + 61
    25  Pro                                 0x0000000104d6bf40 $s3Pro0A3AppV5$mainyyFZ + 48
    26  Pro                                 0x0000000104d6bfd4 main + 20
    27  libdyld.dylib                       0x000000011ac19bbd start + 1

示例代碼如下所示

struct ParentView: View { 

@Environment(\.presentationMode) var presentationMode


    var body: some View {
      mainButton 
    .sheet(
            item: $viewModel.item,
            onDismiss: {
               
            },
            content: { summary in
               ChildView()
            }
        )

}

} 

Answer 1

好的，我找到了解決方案。 導致問題的原因是，當有Environment(.presentationMode)時，對此視圖進行了一些刷新。sheet(item:) 依賴於需要 id 的 Identifiable 類型。 它有這個 id，但如果它使用帶有 like 的可選標識符

var id: String { myId ?? UUID().uuidString } 

當沒有這個環境時，這個底層 model id 不會改變，但是環境屬性底層項目 model 已經重新計算了 id，它通過嘗試兩次呈現這個視圖而導致問題。