Replace deprecated [UIScreen mainScreen] in FlutterViewController.mm and FlutterViewControllerTest.mm (flutter#43690)

Issue: flutter#128260

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide] and the [C++,
Objective-C, Java style guides].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making or feature I am
adding, or Hixie said the PR is test-exempt. See [testing the engine]
for instructions on writing and running engine tests.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I signed the [CLA].
- [x] All existing and new tests are passing.

Author: mossmana

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

@@ -477,10 +477,30 @@ - (void)loadView {
   return pointer_data;
 }
 
-static void SendFakeTouchEvent(FlutterEngine* engine,
+- (UIWindowScene*)windowSceneIfViewLoaded {
+  if (self.viewIfLoaded == nil) {
+    FML_LOG(WARNING) << "Trying to access the window scene before the view is loaded.";
+    return nil;
+  }
+  return self.viewIfLoaded.window.windowScene;
+}
+
+- (UIScreen*)screenIfViewLoaded {
+  if (@available(iOS 13.0, *)) {
+    if (self.viewIfLoaded == nil) {
+      FML_LOG(WARNING) << "Trying to access the screen before the view is loaded.";
+      return nil;
+    }
+    return [self windowSceneIfViewLoaded].screen;
+  }
+  return UIScreen.mainScreen;
+}
+
+static void SendFakeTouchEvent(UIScreen* screen,
+                               FlutterEngine* engine,
                                CGPoint location,
                                flutter::PointerData::Change change) {
-  const CGFloat scale = [UIScreen mainScreen].scale;
+  const CGFloat scale = screen.scale;
   flutter::PointerData pointer_data = [[engine viewController] generatePointerDataForFake];
   pointer_data.physical_x = location.x * scale;
   pointer_data.physical_y = location.y * scale;
@@ -495,8 +515,11 @@ - (BOOL)scrollViewShouldScrollToTop:(UIScrollView*)scrollView {
     return NO;
   }
   CGPoint statusBarPoint = CGPointZero;
-  SendFakeTouchEvent(_engine.get(), statusBarPoint, flutter::PointerData::Change::kDown);
-  SendFakeTouchEvent(_engine.get(), statusBarPoint, flutter::PointerData::Change::kUp);
+  UIScreen* screen = [self screenIfViewLoaded];
+  if (screen) {
+    SendFakeTouchEvent(screen, _engine.get(), statusBarPoint, flutter::PointerData::Change::kDown);
+    SendFakeTouchEvent(screen, _engine.get(), statusBarPoint, flutter::PointerData::Change::kUp);
+  }
   return NO;
 }
 
@@ -613,24 +636,6 @@ - (SpringAnimation*)keyboardSpringAnimation {
   return _keyboardSpringAnimation.get();
 }
 
-- (UIScreen*)mainScreenIfViewLoaded {
-  if (@available(iOS 13.0, *)) {
-    if (self.viewIfLoaded == nil) {
-      FML_LOG(WARNING) << "Trying to access the view before it is loaded.";
-    }
-    return [self windowSceneIfViewLoaded].screen;
-  }
-  return UIScreen.mainScreen;
-}
-
-- (UIWindowScene*)windowSceneIfViewLoaded {
-  if (self.viewIfLoaded == nil) {
-    FML_LOG(WARNING) << "Trying to access the view before it is loaded.";
-    return nil;
-  }
-  return self.viewIfLoaded.window.windowScene;
-}
-
 - (BOOL)loadDefaultSplashScreenView {
   NSString* launchscreenName =
       [[[NSBundle mainBundle] infoDictionary] objectForKey:@"UILaunchStoryboardName"];
@@ -1065,7 +1070,7 @@ - (void)dispatchTouches:(NSSet*)touches
   // Activate or pause the correction of delivery frame rate of touch events.
   [self triggerTouchRateCorrectionIfNeeded:touches];
 
-  const CGFloat scale = [UIScreen mainScreen].scale;
+  const CGFloat scale = [self screenIfViewLoaded].scale;
   auto packet =
       std::make_unique<flutter::PointerDataPacket>(touches.count + touches_to_remove_count);
 
@@ -1280,7 +1285,7 @@ - (void)updateViewportMetricsIfNeeded {
 
 - (void)viewDidLayoutSubviews {
   CGRect viewBounds = self.view.bounds;
-  CGFloat scale = [UIScreen mainScreen].scale;
+  CGFloat scale = [self screenIfViewLoaded].scale;
 
   // Purposefully place this not visible.
   _scrollView.get().frame = CGRectMake(0.0, 0.0, viewBounds.size.width, 0.0);
@@ -1327,12 +1332,12 @@ - (void)viewSafeAreaInsetsDidChange {
 
 // Set _viewportMetrics physical size.
 - (void)setViewportMetricsSize {
-  UIScreen* mainScreen = [self mainScreenIfViewLoaded];
-  if (!mainScreen) {
+  UIScreen* screen = [self screenIfViewLoaded];
+  if (!screen) {
     return;
   }
 
-  CGFloat scale = mainScreen.scale;
+  CGFloat scale = screen.scale;
   _viewportMetrics.physical_width = self.view.bounds.size.width * scale;
   _viewportMetrics.physical_height = self.view.bounds.size.height * scale;
 }
@@ -1341,12 +1346,12 @@ - (void)setViewportMetricsSize {
 //
 // Viewport paddings represent the iOS safe area insets.
 - (void)setViewportMetricsPaddings {
-  UIScreen* mainScreen = [self mainScreenIfViewLoaded];
-  if (!mainScreen) {
+  UIScreen* screen = [self screenIfViewLoaded];
+  if (!screen) {
     return;
   }
 
-  CGFloat scale = mainScreen.scale;
+  CGFloat scale = screen.scale;
   _viewportMetrics.physical_padding_top = self.view.safeAreaInsets.top * scale;
   _viewportMetrics.physical_padding_left = self.view.safeAreaInsets.left * scale;
   _viewportMetrics.physical_padding_right = self.view.safeAreaInsets.right * scale;
@@ -1507,7 +1512,7 @@ - (FlutterKeyboardMode)calculateKeyboardAttachMode:(NSNotification*)notification
     return FlutterKeyboardModeHidden;
   }
 
-  CGRect screenRect = [self mainScreenIfViewLoaded].bounds;
+  CGRect screenRect = [self screenIfViewLoaded].bounds;
   CGRect adjustedKeyboardFrame = keyboardFrame;
   adjustedKeyboardFrame.origin.y += [self calculateMultitaskingAdjustment:screenRect
                                                             keyboardFrame:keyboardFrame];
@@ -1547,7 +1552,7 @@ - (CGFloat)calculateMultitaskingAdjustment:(CGRect)screenRect keyboardFrame:(CGR
     }
     CGRect viewRectRelativeToScreen =
         [self.viewIfLoaded convertRect:self.viewIfLoaded.frame
-                     toCoordinateSpace:[self mainScreenIfViewLoaded].coordinateSpace];
+                     toCoordinateSpace:[self screenIfViewLoaded].coordinateSpace];
     CGFloat viewBottom = CGRectGetMaxY(viewRectRelativeToScreen);
     CGFloat offset = screenHeight - viewBottom;
     if (offset > 0) {
@@ -1563,14 +1568,14 @@ - (CGFloat)calculateKeyboardInset:(CGRect)keyboardFrame keyboardMode:(NSInteger)
     // Calculate how much of the keyboard intersects with the view.
     CGRect viewRectRelativeToScreen =
         [self.viewIfLoaded convertRect:self.viewIfLoaded.frame
-                     toCoordinateSpace:[self mainScreenIfViewLoaded].coordinateSpace];
+                     toCoordinateSpace:[self screenIfViewLoaded].coordinateSpace];
     CGRect intersection = CGRectIntersection(keyboardFrame, viewRectRelativeToScreen);
     CGFloat portionOfKeyboardInView = CGRectGetHeight(intersection);
 
     // The keyboard is treated as an inset since we want to effectively reduce the window size by
     // the keyboard height. The Dart side will compute a value accounting for the keyboard-consuming
     // bottom padding.
-    CGFloat scale = [self mainScreenIfViewLoaded].scale;
+    CGFloat scale = [self screenIfViewLoaded].scale;
     return portionOfKeyboardInView * scale;
   }
   return 0;
@@ -1869,9 +1874,8 @@ - (void)performOrientationUpdate:(UIInterfaceOrientationMask)new_preferences {
       if (@available(iOS 13.0, *)) {
         UIWindowScene* windowScene = [self windowSceneIfViewLoaded];
         if (!windowScene) {
-          // When the view is not loaded, it does not make sense to access the interface
-          // orientation, bail.
-          FML_LOG(WARNING) << "Trying to access the window scene before the view is loaded.";
+          FML_LOG(WARNING)
+              << "Accessing the interface orientation when the window scene is unavailable.";
           return;
         }
         currentInterfaceOrientation = 1 << windowScene.interfaceOrientation;
@@ -2291,7 +2295,7 @@ - (BOOL)gestureRecognizer:(UIGestureRecognizer*)gestureRecognizer
 
 - (void)hoverEvent:(UIPanGestureRecognizer*)recognizer API_AVAILABLE(ios(13.4)) {
   CGPoint location = [recognizer locationInView:self.view];
-  CGFloat scale = [UIScreen mainScreen].scale;
+  CGFloat scale = [self screenIfViewLoaded].scale;
   CGPoint oldLocation = _mouseState.location;
   _mouseState.location = {location.x * scale, location.y * scale};
 
@@ -2348,7 +2352,7 @@ - (void)hoverEvent:(UIPanGestureRecognizer*)recognizer API_AVAILABLE(ios(13.4))
 
 - (void)discreteScrollEvent:(UIPanGestureRecognizer*)recognizer API_AVAILABLE(ios(13.4)) {
   CGPoint translation = [recognizer translationInView:self.view];
-  const CGFloat scale = [UIScreen mainScreen].scale;
+  const CGFloat scale = [self screenIfViewLoaded].scale;
 
   translation.x *= scale;
   translation.y *= scale;
@@ -2377,7 +2381,7 @@ - (void)discreteScrollEvent:(UIPanGestureRecognizer*)recognizer API_AVAILABLE(io
 
 - (void)continuousScrollEvent:(UIPanGestureRecognizer*)recognizer API_AVAILABLE(ios(13.4)) {
   CGPoint translation = [recognizer translationInView:self.view];
-  const CGFloat scale = [UIScreen mainScreen].scale;
+  const CGFloat scale = [self screenIfViewLoaded].scale;
 
   flutter::PointerData pointer_data = [self generatePointerDataAtLastMouseLocation];
   pointer_data.device = reinterpret_cast<int64_t>(recognizer);