onDisappear called immediately after hosting the view

[Karllas]

Is it a bug or expected behaviour that onDisappear closure get's called straight after the view is hosted?

[nalexn]

It depends on the structure of your test. Please provide the sample code that illustrates the issue.

[bdbergeron]

I'm encountering this issue when running tests for my custom view modifier on macOS, but running them on iOS does not exhibit this behavior and my test cases run successfully.

Here's my custom view modifier:

extension View {
  public func autoUpdating(updater: AutoUpdater, updateInterval: TimeInterval) -> some View {
    modifier(AutoUpdaterViewModifier(autoUpdater: updater, updateInterval: updateInterval))
  }
}

struct AutoUpdaterViewModifier: ViewModifier {

  #if os(iOS)
  static let foregroundNotification = UIApplication.didBecomeActiveNotification
  static let backgroundNotification = UIApplication.didEnterBackgroundNotification
  #elseif os(macOS)
  static let foregroundNotification = NSApplication.didBecomeActiveNotification
  static let backgroundNotification = NSApplication.didResignActiveNotification
  #endif

  let autoUpdater: AutoUpdater
  let updateInterval: TimeInterval

  func body(content: Content) -> some View {
    content
      .onAppear {
        autoUpdater.enable(updateInterval: updateInterval)
      }
      .onDisappear {
        autoUpdater.disable()
      }
      .onReceive(NotificationCenter.default.publisher(for: Self.foregroundNotification)) { _ in
        autoUpdater.enable(updateInterval: updateInterval)
      }
      .onReceive(NotificationCenter.default.publisher(for: Self.backgroundNotification)) { _ in
        autoUpdater.disable()
      }
  }

}

The view I'm using in my tests:

private struct TestView: View {
  let autoUpdater: AutoUpdater
  let updateInterval: TimeInterval
  var didAppear: ((Self) -> Void)?

  var body: some View {
    Text("Hello, world!")
      .onAppear {
        didAppear?(self)
      }
      .autoUpdating(updater: autoUpdater, updateInterval: updateInterval)
  }
}

And an example test case for when the app is backgrounded:

  func test_viewModifier_background() throws {
    let autoUpdater = AutoUpdater()
    var view = TestView(autoUpdater: autoUpdater, updateInterval: 0.25)
    let viewExpectation = view.on(\.didAppear) { _ in }
    ViewHosting.host(view: view)
    wait(for: [viewExpectation], timeout: 1.0)

    XCTAssertEqual(autoUpdater.isEnabled, true) // triggered by modifier's onAppear

    let notification = AutoUpdaterViewModifier.backgroundNotification
    let notificationExpectation = expectation(forNotification: notification, object: nil)
    NotificationCenter.default.post(name: notification, object: nil)
    wait(for: [notificationExpectation], timeout: 1.0)

    XCTAssertEqual(autoUpdater.isEnabled, false) // triggered by modifier's onReceive
  }

When running that test targeting an iOS device, it succeeds every time, and the order in which the view modifiers inside AutoUpdaterViewModifier are called is what one would expect: onAppear, onReceive, and onDisappear. When running the test targeting my Mac, however, the test fails and the order is always onAppear, onDisappear , and then onReceive .

Stack trace shows both the onAppear and onDisappear being triggered by the call to window.layoutIfNeeded() inside ViewHosting.host(). Further, I'm seeing this log message in the Xcode console:

2023-09-29 20:05:00.946192-0400 xctest[32700:9428330] [Window] Warning: Window NSWindow 0x10381cde0 ordered front from a non-active application and may order beneath the active application's windows.