Issues/39832 reland (#13642)

* Reland "Added new lifecycle enum (#11913)"

lib/ui/window.dart

@@ -171,18 +171,16 @@ enum AppLifecycleState {
   ///
   /// When the application is in this state, the engine will not call the
   /// [Window.onBeginFrame] and [Window.onDrawFrame] callbacks.
-  ///
-  /// Android apps in this state should assume that they may enter the
-  /// [suspending] state at any time.
   paused,
 
-  /// The application will be suspended momentarily.
-  ///
-  /// When the application is in this state, the engine will not call the
-  /// [Window.onBeginFrame] and [Window.onDrawFrame] callbacks.
+  /// The application is still hosted on a flutter engine but is detached from
+  /// any host views.
   ///
-  /// On iOS, this state is currently unused.
-  suspending,
+  /// When the application is in this state, the engine is running without
+  /// a view. It can either be in the progress of attaching a view when engine
+  /// was first initializes, or after the view being destroyed due to a Navigator
+  /// pop.
+  detached,
 }
 
 /// A representation of distances for each of the four edges of a rectangle,

lib/web_ui/lib/src/ui/window.dart

@@ -73,18 +73,13 @@ enum AppLifecycleState {
   ///
   /// When the application is in this state, the engine will not call the
   /// [Window.onBeginFrame] and [Window.onDrawFrame] callbacks.
-  ///
-  /// Android apps in this state should assume that they may enter the
-  /// [suspending] state at any time.
   paused,
 
-  /// The application will be suspended momentarily.
-  ///
-  /// When the application is in this state, the engine will not call the
-  /// [Window.onBeginFrame] and [Window.onDrawFrame] callbacks.
+  /// The application is detached from view.
   ///
-  /// On iOS, this state is currently unused.
-  suspending,
+  /// When the application is in this state, the engine is running without
+  /// a platform UI.
+  detached,
 }
 
 /// A representation of distances for each of the four edges of a rectangle,

runtime/runtime_controller.h

@@ -120,7 +120,7 @@ class RuntimeController final : public WindowClient {
     std::string variant_code;
     std::vector<std::string> locale_data;
     std::string user_settings_data = "{}";
-    std::string lifecycle_state;
+    std::string lifecycle_state = "AppLifecycleState.detached";
     bool semantics_enabled = false;
     bool assistive_technology_enabled = false;
     int32_t accessibility_feature_flags_ = 0;

shell/common/engine.cc

@@ -311,7 +311,7 @@ bool Engine::HandleLifecyclePlatformMessage(PlatformMessage* message) {
   const auto& data = message->data();
   std::string state(reinterpret_cast<const char*>(data.data()), data.size());
   if (state == "AppLifecycleState.paused" ||
-      state == "AppLifecycleState.suspending") {
+      state == "AppLifecycleState.detached") {
     activity_running_ = false;
     StopAnimator();
   } else if (state == "AppLifecycleState.resumed" ||

shell/platform/android/io/flutter/embedding/android/FlutterActivityAndFragmentDelegate.java

@@ -461,6 +461,8 @@ void onDetach() {
       platformPlugin = null;
     }
 
+    flutterEngine.getLifecycleChannel().appIsDetached();
+
     // Destroy our FlutterEngine if we're not set to retain it.
     if (host.shouldDestroyEngineWithHost()) {
       flutterEngine.destroy();

shell/platform/android/io/flutter/embedding/engine/systemchannels/LifecycleChannel.java

@@ -39,4 +39,8 @@ public void appIsPaused() {
     channel.send("AppLifecycleState.paused");
   }
 
+  public void appIsDetached() {
+    Log.v(TAG, "Sending AppLifecycleState.detached message.");
+    channel.send("AppLifecycleState.detached");
+  }
 }

shell/platform/android/test/io/flutter/embedding/android/FlutterActivityAndFragmentDelegateTest.java

@@ -85,18 +85,21 @@ public void itSendsLifecycleEventsToFlutter() {
     verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsResumed();
     verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsPaused();
     verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsInactive();
+    verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsDetached();
 
     // When the Activity/Fragment is resumed, a resumed message should have been sent to Flutter.
     delegate.onResume();
     verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsResumed();
     verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsInactive();
     verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsPaused();
+    verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsDetached();
 
     // When the Activity/Fragment is paused, an inactive message should have been sent to Flutter.
     delegate.onPause();
     verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsResumed();
     verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsInactive();
     verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsPaused();
+    verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsDetached();
 
     // When the Activity/Fragment is stopped, a paused message should have been sent to Flutter.
     // Notice that Flutter uses the term "paused" in a different way, and at a different time
@@ -105,6 +108,14 @@ public void itSendsLifecycleEventsToFlutter() {
     verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsResumed();
     verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsInactive();
     verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsPaused();
+    verify(mockFlutterEngine.getLifecycleChannel(), never()).appIsDetached();
+
+    // When activity detaches, a detached message should have been sent to Flutter.
+    delegate.onDetach();
+    verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsResumed();
+    verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsInactive();
+    verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsPaused();
+    verify(mockFlutterEngine.getLifecycleChannel(), times(1)).appIsDetached();
   }
 
   @Test

shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -175,18 +175,23 @@ - (void)ensureSemanticsEnabled {
 
 - (void)setViewController:(FlutterViewController*)viewController {
   FML_DCHECK(self.iosPlatformView);
-  _viewController = [viewController getWeakPtr];
+  _viewController =
+      viewController ? [viewController getWeakPtr] : fml::WeakPtr<FlutterViewController>();
   self.iosPlatformView->SetOwnerViewController(_viewController);
   [self maybeSetupPlatformViewChannels];
 
-  __block FlutterEngine* blockSelf = self;
-  self.flutterViewControllerWillDeallocObserver =
-      [[NSNotificationCenter defaultCenter] addObserverForName:FlutterViewControllerWillDealloc
-                                                        object:viewController
-                                                         queue:[NSOperationQueue mainQueue]
-                                                    usingBlock:^(NSNotification* note) {
-                                                      [blockSelf notifyViewControllerDeallocated];
-                                                    }];
+  if (viewController) {
+    __block FlutterEngine* blockSelf = self;
+    self.flutterViewControllerWillDeallocObserver =
+        [[NSNotificationCenter defaultCenter] addObserverForName:FlutterViewControllerWillDealloc
+                                                          object:viewController
+                                                           queue:[NSOperationQueue mainQueue]
+                                                      usingBlock:^(NSNotification* note) {
+                                                        [blockSelf notifyViewControllerDeallocated];
+                                                      }];
+  } else {
+    self.flutterViewControllerWillDeallocObserver = nil;
+  }
 }
 
 - (void)setFlutterViewControllerWillDeallocObserver:(id<NSObject>)observer {
@@ -201,6 +206,7 @@ - (void)setFlutterViewControllerWillDeallocObserver:(id<NSObject>)observer {
 }
 
 - (void)notifyViewControllerDeallocated {
+  [[self lifecycleChannel] sendMessage:@"AppLifecycleState.detached"];
   if (!_allowHeadlessExecution) {
     [self destroyContext];
   } else {

testing/scenario_app/ios/Scenarios/ScenariosTests/AppLifecycleTests.m

@@ -225,4 +225,70 @@ - (void)testVisibleFlutterViewControllerRespondsToApplicationLifecycle {
   [engine setViewController:nil];
 }
 
+- (void)testFlutterViewControllerDetachingSendsApplicationLifecycle {
+  XCTestExpectation* engineStartedExpectation = [self expectationWithDescription:@"Engine started"];
+
+  // Let the engine finish booting (at the end of which the channels are properly set-up) before
+  // moving onto the next step of showing the next view controller.
+  ScreenBeforeFlutter* rootVC = [[ScreenBeforeFlutter alloc] initWithEngineRunCompletion:^void() {
+    [engineStartedExpectation fulfill];
+  }];
+
+  [self waitForExpectationsWithTimeout:5 handler:nil];
+
+  UIApplication* application = UIApplication.sharedApplication;
+  application.delegate.window.rootViewController = rootVC;
+  FlutterEngine* engine = rootVC.engine;
+
+  NSMutableArray* lifecycleExpectations = [NSMutableArray arrayWithCapacity:10];
+
+  // Expected sequence from showing the FlutterViewController is inactive and resumed.
+  [lifecycleExpectations addObjectsFromArray:@[
+    [[XCAppLifecycleTestExpectation alloc] initForLifecycle:@"AppLifecycleState.inactive"
+                                                    forStep:@"showing a FlutterViewController"],
+    [[XCAppLifecycleTestExpectation alloc] initForLifecycle:@"AppLifecycleState.resumed"
+                                                    forStep:@"showing a FlutterViewController"]
+  ]];
+  // At the end of Flutter VC, we want to make sure it deallocs and sends detached signal.
+  // Using autoreleasepool will guarantee that.
+  FlutterViewController* flutterVC;
+  @autoreleasepool {
+    flutterVC = [rootVC showFlutter];
+    [engine.lifecycleChannel setMessageHandler:^(id message, FlutterReply callback) {
+      if (lifecycleExpectations.count == 0) {
+        XCTFail(@"Unexpected lifecycle transition: %@", message);
+        return;
+      }
+      XCAppLifecycleTestExpectation* nextExpectation = [lifecycleExpectations objectAtIndex:0];
+      if (![[nextExpectation expectedLifecycle] isEqualToString:message]) {
+        XCTFail(@"Expected lifecycle %@ but instead received %@",
+                [nextExpectation expectedLifecycle], message);
+        return;
+      }
+
+      [nextExpectation fulfill];
+      [lifecycleExpectations removeObjectAtIndex:0];
+    }];
+
+    [self waitForExpectations:lifecycleExpectations timeout:5];
+
+    // Starts dealloc flutter VC.
+    [lifecycleExpectations addObjectsFromArray:@[
+      [[XCAppLifecycleTestExpectation alloc] initForLifecycle:@"AppLifecycleState.inactive"
+                                                      forStep:@"detaching a FlutterViewController"],
+      [[XCAppLifecycleTestExpectation alloc] initForLifecycle:@"AppLifecycleState.paused"
+                                                      forStep:@"detaching a FlutterViewController"],
+      [[XCAppLifecycleTestExpectation alloc]
+          initForLifecycle:@"AppLifecycleState.detached"
+                   forStep:@"detaching a FlutterViewController"]
+    ]];
+    [flutterVC dismissViewControllerAnimated:NO completion:nil];
+    flutterVC = nil;
+  }
+  [self waitForExpectations:lifecycleExpectations timeout:5];
+
+  [engine.lifecycleChannel setMessageHandler:nil];
+  [engine setViewController:nil];
+}
+
 @end