Add isDisplayingFlutterUI to FlutterViewController (flutter/engine#10816)

engine/src/flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h

@@ -130,6 +130,14 @@ FLUTTER_EXPORT
  */
 - (id<FlutterPluginRegistry>)pluginRegistry;
 
+/**
+ * True if at least one frame has rendered and the ViewController has appeared.
+ *
+ * This property is reset to false when the ViewController disappears. It is
+ * guaranteed to only alternate between true and false for observers.
+ */
+@property(nonatomic, readonly, getter=isDisplayingFlutterUI) BOOL displayingFlutterUI;
+
 /**
  * Specifies the view to use as a splash screen. Flutter's rendering is asynchronous, so the first
  * frame rendered by the Flutter application might not immediately appear when theFlutter view is

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -29,6 +29,7 @@ NSNotificationName const FlutterSemanticsUpdateNotification = @"FlutterSemantics
 // change. Unfortunately unless you have Werror turned on, incompatible pointers as arguments are
 // just a warning.
 @interface FlutterViewController () <FlutterBinaryMessenger>
+@property(nonatomic, readwrite, getter=isDisplayingFlutterUI) BOOL displayingFlutterUI;
 @end
 
 @implementation FlutterViewController {
@@ -49,6 +50,8 @@ NSNotificationName const FlutterSemanticsUpdateNotification = @"FlutterSemantics
   NSMutableSet<NSNumber*>* _ongoingTouches;
 }
 
+@synthesize displayingFlutterUI = _displayingFlutterUI;
+
 #pragma mark - Manage and override all designated initializers
 
 - (instancetype)initWithEngine:(FlutterEngine*)engine
@@ -263,7 +266,25 @@ NSNotificationName const FlutterSemanticsUpdateNotification = @"FlutterSemantics
   [self.view addSubview:splashScreenView];
 }
 
++ (BOOL)automaticallyNotifiesObserversOfDisplayingFlutterUI {
+  return NO;
+}
+
+- (void)setDisplayingFlutterUI:(BOOL)displayingFlutterUI {
+  if (_displayingFlutterUI != displayingFlutterUI) {
+    if (displayingFlutterUI == YES) {
+      if (!self.isViewLoaded || !self.view.window) {
+        return;
+      }
+    }
+    [self willChangeValueForKey:@"displayingFlutterUI"];
+    _displayingFlutterUI = displayingFlutterUI;
+    [self didChangeValueForKey:@"displayingFlutterUI"];
+  }
+}
+
 - (void)callViewRenderedCallback {
+  self.displayingFlutterUI = YES;
   if (_flutterViewRenderedCallback != nil) {
     _flutterViewRenderedCallback.get()();
     _flutterViewRenderedCallback.reset();
@@ -395,6 +416,7 @@ NSNotificationName const FlutterSemanticsUpdateNotification = @"FlutterSemantics
     [_engine.get() platformViewsController] -> SetFlutterViewController(self);
     [_engine.get() platformView] -> NotifyCreated();
   } else {
+    self.displayingFlutterUI = NO;
     [_engine.get() platformView] -> NotifyDestroyed();
     [_engine.get() platformViewsController] -> SetFlutterView(nullptr);
     [_engine.get() platformViewsController] -> SetFlutterViewController(nullptr);

engine/src/flutter/testing/scenario_app/ios/Scenarios/ScenariosTests/FlutterViewControllerTest.m

@@ -25,25 +25,31 @@
 }
 
 - (void)testFirstFrameCallback {
+  XCTestExpectation* firstFrameRendered = [self expectationWithDescription:@"firstFrameRendered"];
+
   FlutterEngine* engine = [[FlutterEngine alloc] initWithName:@"test" project:nil];
   [engine runWithEntrypoint:nil];
   self.flutterViewController = [[FlutterViewController alloc] initWithEngine:engine
                                                                      nibName:nil
                                                                       bundle:nil];
-  __block BOOL shouldKeepRunning = YES;
+
+  XCTAssertFalse(self.flutterViewController.isDisplayingFlutterUI);
+
+  XCTestExpectation* displayingFlutterUIExpectation =
+      [self keyValueObservingExpectationForObject:self.flutterViewController
+                                          keyPath:@"displayingFlutterUI"
+                                    expectedValue:@YES];
+  displayingFlutterUIExpectation.assertForOverFulfill = YES;
+
   [self.flutterViewController setFlutterViewDidRenderCallback:^{
-    shouldKeepRunning = NO;
+    [firstFrameRendered fulfill];
   }];
+
   AppDelegate* appDelegate = (AppDelegate*)UIApplication.sharedApplication.delegate;
   UIViewController* rootVC = appDelegate.window.rootViewController;
   [rootVC presentViewController:self.flutterViewController animated:NO completion:nil];
-  NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
-  int countDownMs = 2000;
-  while (shouldKeepRunning && countDownMs > 0) {
-    [runLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate dateWithTimeIntervalSinceNow:0.1]];
-    countDownMs -= 100;
-  }
-  XCTAssertGreaterThan(countDownMs, 0);
+
+  [self waitForExpectationsWithTimeout:30.0 handler:nil];
 }
 
 @end