[iOS] Support keyboard animation on iOS (flutter/engine#29281)

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

@@ -69,6 +69,12 @@ typedef struct MouseState {
 @property(nonatomic, assign) BOOL isHomeIndicatorHidden;
 @property(nonatomic, assign) BOOL isPresentingViewControllerAnimating;
 
+/**
+ * Keyboard animation properties
+ */
+@property(nonatomic, assign) double targetViewInsetBottom;
+@property(nonatomic, strong) CADisplayLink* displayLink;
+
 /**
  * Creates and registers plugins used by this view controller.
  */
@@ -113,6 +119,7 @@ typedef enum UIAccessibilityContrast : NSInteger {
   fml::scoped_nsobject<UIScrollView> _scrollView;
   fml::scoped_nsobject<UIPointerInteraction> _pointerInteraction API_AVAILABLE(ios(13.4));
   fml::scoped_nsobject<UIPanGestureRecognizer> _panGestureRecognizer API_AVAILABLE(ios(13.4));
+  fml::scoped_nsobject<UIView> _keyboardAnimationView;
   MouseState _mouseState;
 }
 
@@ -542,6 +549,10 @@ static void sendFakeTouchEvent(FlutterEngine* engine,
   return _splashScreenView.get();
 }
 
+- (UIView*)keyboardAnimationView {
+  return _keyboardAnimationView.get();
+}
+
 - (BOOL)loadDefaultSplashScreenView {
   NSString* launchscreenName =
       [[[NSBundle mainBundle] infoDictionary] objectForKey:@"UILaunchStoryboardName"];
@@ -719,6 +730,8 @@ static void sendFakeTouchEvent(FlutterEngine* engine,
 - (void)viewDidDisappear:(BOOL)animated {
   TRACE_EVENT0("flutter", "viewDidDisappear");
   if ([_engine.get() viewController] == self) {
+    [self invalidateDisplayLink];
+    [self ensureViewportMetricsIsCorrect];
     [self surfaceUpdated:NO];
     [[_engine.get() lifecycleChannel] sendMessage:@"AppLifecycleState.paused"];
     [self flushOngoingTouches];
@@ -1104,29 +1117,115 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
     }
   }
 
+  // Ignore keyboard notifications if engine’s viewController is not current viewController.
+  if ([_engine.get() viewController] != self) {
+    return;
+  }
+
   CGRect keyboardFrame = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue];
   CGRect screenRect = [[UIScreen mainScreen] bounds];
 
+  // Get the animation duration
+  NSTimeInterval duration =
+      [[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];
+
   // Considering the iPad's split keyboard, Flutter needs to check if the keyboard frame is present
   // in the screen to see if the keyboard is visible.
   if (CGRectIntersectsRect(keyboardFrame, screenRect)) {
     CGFloat bottom = CGRectGetHeight(keyboardFrame);
     CGFloat scale = [UIScreen mainScreen].scale;
-
     // 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.
-    _viewportMetrics.physical_view_inset_bottom = bottom * scale;
+    self.targetViewInsetBottom = bottom * scale;
   } else {
-    _viewportMetrics.physical_view_inset_bottom = 0;
+    self.targetViewInsetBottom = 0;
   }
-
-  [self updateViewportMetrics];
+  [self startKeyBoardAnimation:duration];
 }
 
 - (void)keyboardWillBeHidden:(NSNotification*)notification {
-  _viewportMetrics.physical_view_inset_bottom = 0;
-  [self updateViewportMetrics];
+  // When keyboard hide, the keyboardWillChangeFrame function will be called to update viewport
+  // metrics. So do not call [self updateViewportMetrics] here again.
+}
+
+- (void)startKeyBoardAnimation:(NSTimeInterval)duration {
+  // If current physical_view_inset_bottom == targetViewInsetBottom,do nothing.
+  if (_viewportMetrics.physical_view_inset_bottom == self.targetViewInsetBottom) {
+    return;
+  }
+
+  // When call this method first time,
+  // initialize the keyboardAnimationView to get animation interpolation during animation.
+  if ([self keyboardAnimationView] == nil) {
+    UIView* keyboardAnimationView = [[UIView alloc] init];
+    [keyboardAnimationView setHidden:YES];
+    _keyboardAnimationView.reset(keyboardAnimationView);
+  }
+
+  if ([self keyboardAnimationView].superview == nil) {
+    [self.view addSubview:[self keyboardAnimationView]];
+  }
+
+  // Remove running animation when start another animation.
+  // After calling this line,the old display link will invalidate.
+  [[self keyboardAnimationView].layer removeAllAnimations];
+
+  // Set animation begin value.
+  [self keyboardAnimationView].frame =
+      CGRectMake(0, _viewportMetrics.physical_view_inset_bottom, 0, 0);
+
+  // Invalidate old display link if the old animation is not complete
+  [self invalidateDisplayLink];
+
+  self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(onDisplayLink)];
+  [self.displayLink addToRunLoop:NSRunLoop.currentRunLoop forMode:NSRunLoopCommonModes];
+  __block CADisplayLink* currentDisplayLink = self.displayLink;
+
+  [UIView animateWithDuration:duration
+      animations:^{
+        // Set end value.
+        [self keyboardAnimationView].frame = CGRectMake(0, self.targetViewInsetBottom, 0, 0);
+      }
+      completion:^(BOOL finished) {
+        if (self.displayLink == currentDisplayLink) {
+          [self invalidateDisplayLink];
+        }
+        if (finished) {
+          [self removeKeyboardAnimationView];
+          [self ensureViewportMetricsIsCorrect];
+        }
+      }];
+}
+
+- (void)invalidateDisplayLink {
+  [self.displayLink invalidate];
+}
+
+- (void)removeKeyboardAnimationView {
+  if ([self keyboardAnimationView].superview != nil) {
+    [[self keyboardAnimationView] removeFromSuperview];
+  }
+}
+
+- (void)ensureViewportMetricsIsCorrect {
+  if (_viewportMetrics.physical_view_inset_bottom != self.targetViewInsetBottom) {
+    // Make sure the `physical_view_inset_bottom` is the target value.
+    _viewportMetrics.physical_view_inset_bottom = self.targetViewInsetBottom;
+    [self updateViewportMetrics];
+  }
+}
+
+- (void)onDisplayLink {
+  if ([self keyboardAnimationView].superview == nil) {
+    // Ensure the keyboardAnimationView is in view hierarchy when animation running.
+    [self.view addSubview:[self keyboardAnimationView]];
+  }
+  if ([self keyboardAnimationView].layer.presentationLayer) {
+    CGFloat value = [self keyboardAnimationView].layer.presentationLayer.frame.origin.y;
+    _viewportMetrics.physical_view_inset_bottom = value;
+    [self updateViewportMetrics];
+  }
 }
 
 - (void)handlePressEvent:(FlutterUIPressProxy*)press

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

@@ -124,6 +124,10 @@ typedef enum UIAccessibilityContrast : NSInteger {
 - (void)scrollEvent:(UIPanGestureRecognizer*)recognizer;
 - (void)updateViewportMetrics;
 - (void)onUserSettingsChanged:(NSNotification*)notification;
+- (void)keyboardWillChangeFrame:(NSNotification*)notification;
+- (void)startKeyBoardAnimation:(NSTimeInterval)duration;
+- (void)ensureViewportMetricsIsCorrect;
+- (void)invalidateDisplayLink;
 @end
 
 @interface FlutterViewControllerTest : XCTestCase
@@ -151,6 +155,41 @@ typedef enum UIAccessibilityContrast : NSInteger {
   self.messageSent = nil;
 }
 
+- (void)testkeyboardWillChangeFrameWillStartKeyboardAnimation {
+  FlutterEngine* mockEngine = OCMPartialMock([[FlutterEngine alloc] init]);
+  [mockEngine createShell:@"" libraryURI:@"" initialRoute:nil];
+  FlutterViewController* viewController = [[FlutterViewController alloc] initWithEngine:mockEngine
+                                                                                nibName:nil
+                                                                                 bundle:nil];
+
+  CGFloat width = UIScreen.mainScreen.bounds.size.width;
+  CGRect keyboardFrame = CGRectMake(0, 100, width, 400);
+  BOOL isLocal = YES;
+  NSNotification* notification = [NSNotification
+      notificationWithName:@""
+                    object:nil
+                  userInfo:@{
+                    @"UIKeyboardFrameEndUserInfoKey" : [NSValue valueWithCGRect:keyboardFrame],
+                    @"UIKeyboardAnimationDurationUserInfoKey" : [NSNumber numberWithDouble:0.25],
+                    @"UIKeyboardIsLocalUserInfoKey" : [NSNumber numberWithBool:isLocal]
+                  }];
+  id viewControllerMock = OCMPartialMock(viewController);
+  [viewControllerMock keyboardWillChangeFrame:notification];
+  OCMVerify([viewControllerMock startKeyBoardAnimation:0.25]);
+}
+
+- (void)testEnsureViewportMetricsWillInvokeAndDisplayLinkWillInvalidateInViewDidDisappear {
+  FlutterEngine* mockEngine = OCMPartialMock([[FlutterEngine alloc] init]);
+  [mockEngine createShell:@"" libraryURI:@"" initialRoute:nil];
+  FlutterViewController* viewController = [[FlutterViewController alloc] initWithEngine:mockEngine
+                                                                                nibName:nil
+                                                                                 bundle:nil];
+  id viewControllerMock = OCMPartialMock(viewController);
+  [viewControllerMock viewDidDisappear:YES];
+  OCMVerify([viewControllerMock ensureViewportMetricsIsCorrect]);
+  OCMVerify([viewControllerMock invalidateDisplayLink]);
+}
+
 - (void)testViewDidDisappearDoesntPauseEngineWhenNotTheViewController {
   id lifecycleChannel = OCMClassMock([FlutterBasicMessageChannel class]);
   FlutterEnginePartialMock* mockEngine = [[FlutterEnginePartialMock alloc] init];