Fix iOS text field input keyboard flickering & crash (flutter/engine#20805)

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

@@ -1121,7 +1121,7 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
 
 - (void)showTextInput {
   _activeView.textInputDelegate = _textInputDelegate;
-  [self addToKeyWindowIfNeeded:_activeView];
+  [self addToInputParentViewIfNeeded:_activeView];
   [_activeView becomeFirstResponder];
 }
 
@@ -1143,10 +1143,11 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
   }
 
   [self cleanUpViewHierarchy:YES clearText:!saveEntries];
-  [self addToKeyWindowIfNeeded:_activeView];
+  [self addToInputParentViewIfNeeded:_activeView];
 }
 
 - (void)setTextInputClient:(int)client withConfiguration:(NSDictionary*)configuration {
+  [self resetAllClientIds];
   // Hide all input views from autofill, only make those in the new configuration visible
   // to autofill.
   [self changeInputViewsAutofillVisibility:NO];
@@ -1168,11 +1169,19 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
       break;
   }
 
-  // Clean up views that should no longer be in the view hierarchy according to the
-  // updated autofill context.
-  [self cleanUpViewHierarchy:NO clearText:YES];
   [_activeView setTextInputClient:client];
   [_activeView reloadInputViews];
+
+  // Clean up views that no longer need to be in the view hierarchy, according to
+  // the current autofill context. The "garbage" input views are already made
+  // invisible to autofill and they can't `becomeFirstResponder`, we only remove
+  // them to free up resources and reduce the number of input views in the view
+  // hierarchy.
+  //
+  // This is scheduled on the runloop and delayed by 0.1s so we don't remove the
+  // text fields immediately (which seems to make the keyboard flicker).
+  // See: https://github.com/flutter/flutter/issues/64628.
+  [self performSelector:@selector(collectGarbageInputViews) withObject:nil afterDelay:0.1];
 }
 
 // Updates and shows an input field that is not password related and has no autofill
@@ -1188,7 +1197,7 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
   }
 
   [_reusableInputView configureWithDictionary:configuration];
-  [self addToKeyWindowIfNeeded:_reusableInputView];
+  [self addToInputParentViewIfNeeded:_reusableInputView];
   _reusableInputView.textInputDelegate = _textInputDelegate;
 
   for (NSDictionary* field in configuration[kAssociatedAutofillFields]) {
@@ -1253,7 +1262,7 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
     inputView =
         needsPasswordAutofill ? [FlutterSecureTextInputView alloc] : [FlutterTextInputView alloc];
     inputView = [[inputView init] autorelease];
-    [self addToKeyWindowIfNeeded:inputView];
+    [self addToInputParentViewIfNeeded:inputView];
   }
 
   inputView.textInputDelegate = _textInputDelegate;
@@ -1261,23 +1270,27 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
   return inputView;
 }
 
-// Removes every installed input field, unless it's in the current autofill
-// context. May remove the active view too if includeActiveView is YES.
-// When clearText is YES, the text on the input fields will be set to empty before
-// they are removed from the view hierarchy, to avoid autofill save .
-- (void)cleanUpViewHierarchy:(BOOL)includeActiveView clearText:(BOOL)clearText {
+// The UIView to add FlutterTextInputViews to.
+- (UIView*)textInputParentView {
   UIWindow* keyWindow = [UIApplication sharedApplication].keyWindow;
   NSAssert(keyWindow != nullptr,
            @"The application must have a key window since the keyboard client "
            @"must be part of the responder chain to function");
+  return keyWindow;
+}
 
-  for (UIView* view in keyWindow.subviews) {
+// Removes every installed input field, unless it's in the current autofill
+// context. May remove the active view too if includeActiveView is YES.
+// When clearText is YES, the text on the input fields will be set to empty before
+// they are removed from the view hierarchy, to avoid triggering autofill save.
+- (void)cleanUpViewHierarchy:(BOOL)includeActiveView clearText:(BOOL)clearText {
+  for (UIView* view in self.textInputParentView.subviews) {
     if ([view isKindOfClass:[FlutterTextInputView class]] &&
         (includeActiveView || view != _activeView)) {
       FlutterTextInputView* inputView = (FlutterTextInputView*)view;
       if (_autofillContext[inputView.autofillId] != view) {
         if (clearText) {
-          inputView.text.string = @"";
+          [inputView replaceRangeLocal:NSMakeRange(0, inputView.text.length) withText:@""];
         }
         [view removeFromSuperview];
       }
@@ -1285,13 +1298,14 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
   }
 }
 
-- (void)changeInputViewsAutofillVisibility:(BOOL)newVisibility {
-  UIWindow* keyWindow = [UIApplication sharedApplication].keyWindow;
-  NSAssert(keyWindow != nullptr,
-           @"The application must have a key window since the keyboard client "
-           @"must be part of the responder chain to function");
+- (void)collectGarbageInputViews {
+  [self cleanUpViewHierarchy:NO clearText:YES];
+}
 
-  for (UIView* view in keyWindow.subviews) {
+// Changes the visibility of every FlutterTextInputView currently in the
+// view hierarchy.
+- (void)changeInputViewsAutofillVisibility:(BOOL)newVisibility {
+  for (UIView* view in self.textInputParentView.subviews) {
     if ([view isKindOfClass:[FlutterTextInputView class]]) {
       FlutterTextInputView* inputView = (FlutterTextInputView*)view;
       inputView.isVisibleToAutofill = newVisibility;
@@ -1299,14 +1313,21 @@ static FlutterAutofillType autofillTypeOf(NSDictionary* configuration) {
   }
 }
 
-- (void)addToKeyWindowIfNeeded:(FlutterTextInputView*)inputView {
-  UIWindow* keyWindow = [UIApplication sharedApplication].keyWindow;
-  NSAssert(keyWindow != nullptr,
-           @"The application must have a key window since the keyboard client "
-           @"must be part of the responder chain to function");
+// Resets the client id of every FlutterTextInputView in the view hierarchy
+// to 0. Called when a new text input connection will be established.
+- (void)resetAllClientIds {
+  for (UIView* view in self.textInputParentView.subviews) {
+    if ([view isKindOfClass:[FlutterTextInputView class]]) {
+      FlutterTextInputView* inputView = (FlutterTextInputView*)view;
+      [inputView setTextInputClient:0];
+    }
+  }
+}
 
-  if (inputView.window != keyWindow) {
-    [keyWindow addSubview:inputView];
+- (void)addToInputParentViewIfNeeded:(FlutterTextInputView*)inputView {
+  UIView* parentView = self.textInputParentView;
+  if (inputView.superview != parentView) {
+    [parentView addSubview:inputView];
   }
 }
 

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPluginTest.m

@@ -27,6 +27,9 @@ FLUTTER_ASSERT_ARC
 @property(nonatomic, assign) FlutterTextInputView* activeView;
 @property(nonatomic, readonly)
     NSMutableDictionary<NSString*, FlutterTextInputView*>* autofillContext;
+
+- (void)collectGarbageInputViews;
+- (UIView*)textInputParentView;
 @end
 
 @interface FlutterTextInputPluginTest : XCTestCase
@@ -81,12 +84,7 @@ FLUTTER_ASSERT_ARC
 }
 
 - (NSArray<FlutterTextInputView*>*)installedInputViews {
-  UIWindow* keyWindow =
-      [[[UIApplication sharedApplication] windows]
-          filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"isKeyWindow == YES"]]
-          .firstObject;
-
-  return [keyWindow.subviews
+  return [textInputPlugin.textInputParentView.subviews
       filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"self isKindOfClass: %@",
                                                                    [FlutterTextInputView class]]];
 }
@@ -407,6 +405,12 @@ FLUTTER_ASSERT_ARC
   XCTAssertEqual(textInputPlugin.autofillContext.count, 0);
 }
 
+- (void)ensureOnlyActiveViewCanBecomeFirstResponder {
+  for (FlutterTextInputView* inputView in self.installedInputViews) {
+    XCTAssertEqual(inputView.canBecomeFirstResponder, inputView == textInputPlugin.activeView);
+  }
+}
+
 #pragma mark - Autofill - Tests
 
 - (void)testAutofillContext {
@@ -434,8 +438,11 @@ FLUTTER_ASSERT_ARC
   XCTAssertEqual(self.viewsVisibleToAutofill.count, 2);
 
   XCTAssertEqual(textInputPlugin.autofillContext.count, 2);
+
+  [textInputPlugin collectGarbageInputViews];
   XCTAssertEqual(self.installedInputViews.count, 2);
   XCTAssertEqual(textInputPlugin.textInputView, textInputPlugin.autofillContext[@"field1"]);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   // The configuration changes.
   NSMutableDictionary* field3 = self.mutablePasswordTemplateCopy;
@@ -454,8 +461,11 @@ FLUTTER_ASSERT_ARC
 
   XCTAssertEqual(self.viewsVisibleToAutofill.count, 2);
   XCTAssertEqual(textInputPlugin.autofillContext.count, 3);
+
+  [textInputPlugin collectGarbageInputViews];
   XCTAssertEqual(self.installedInputViews.count, 3);
   XCTAssertEqual(textInputPlugin.textInputView, textInputPlugin.autofillContext[@"field1"]);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   // Old autofill input fields are still installed and reused.
   for (NSString* key in oldContext.allKeys) {
@@ -467,9 +477,12 @@ FLUTTER_ASSERT_ARC
 
   oldContext = textInputPlugin.autofillContext;
   [self setClientId:124 configuration:config];
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   XCTAssertEqual(self.viewsVisibleToAutofill.count, 1);
   XCTAssertEqual(textInputPlugin.autofillContext.count, 3);
+
+  [textInputPlugin collectGarbageInputViews];
   XCTAssertEqual(self.installedInputViews.count, 4);
 
   // Old autofill input fields are still installed and reused.
@@ -478,6 +491,7 @@ FLUTTER_ASSERT_ARC
   }
   // The active view should change.
   XCTAssertNotEqual(textInputPlugin.textInputView, textInputPlugin.autofillContext[@"field1"]);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   // Switch to a similar password field, the previous field should be reused.
   oldContext = textInputPlugin.autofillContext;
@@ -486,6 +500,8 @@ FLUTTER_ASSERT_ARC
   // Reuse the input view instance from the last time.
   XCTAssertEqual(self.viewsVisibleToAutofill.count, 1);
   XCTAssertEqual(textInputPlugin.autofillContext.count, 3);
+
+  [textInputPlugin collectGarbageInputViews];
   XCTAssertEqual(self.installedInputViews.count, 4);
 
   // Old autofill input fields are still installed and reused.
@@ -493,6 +509,7 @@ FLUTTER_ASSERT_ARC
     XCTAssertEqual(oldContext[key], textInputPlugin.autofillContext[key]);
   }
   XCTAssertNotEqual(textInputPlugin.textInputView, textInputPlugin.autofillContext[@"field1"]);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 }
 
 - (void)testCommitAutofillContext {
@@ -526,21 +543,27 @@ FLUTTER_ASSERT_ARC
   [self setClientId:123 configuration:config];
   XCTAssertEqual(self.viewsVisibleToAutofill.count, 2);
   XCTAssertEqual(textInputPlugin.autofillContext.count, 2);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   [self commitAutofillContextAndVerify];
   XCTAssertNotEqual(textInputPlugin.textInputView, textInputPlugin.reusableInputView);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   // Install the password field again.
   [self setClientId:123 configuration:config];
   // Switch to a regular autofill group.
   [self setClientId:124 configuration:field3];
   XCTAssertEqual(self.viewsVisibleToAutofill.count, 1);
+
+  [textInputPlugin collectGarbageInputViews];
   XCTAssertEqual(self.installedInputViews.count, 3);
   XCTAssertEqual(textInputPlugin.autofillContext.count, 2);
   XCTAssertNotEqual(textInputPlugin.textInputView, nil);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   [self commitAutofillContextAndVerify];
   XCTAssertNotEqual(textInputPlugin.textInputView, textInputPlugin.reusableInputView);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   // Now switch to an input field that does not autofill.
   [self setClientId:125 configuration:self.mutableTemplateCopy];
@@ -549,11 +572,15 @@ FLUTTER_ASSERT_ARC
   XCTAssertEqual(textInputPlugin.textInputView, textInputPlugin.reusableInputView);
   // The active view should still be installed so it doesn't get
   // deallocated.
+
+  [textInputPlugin collectGarbageInputViews];
   XCTAssertEqual(self.installedInputViews.count, 1);
   XCTAssertEqual(textInputPlugin.autofillContext.count, 0);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   [self commitAutofillContextAndVerify];
   XCTAssertEqual(textInputPlugin.textInputView, textInputPlugin.reusableInputView);
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 }
 
 - (void)testAutofillInputViews {
@@ -577,6 +604,7 @@ FLUTTER_ASSERT_ARC
   [config setValue:@[ field1, field2 ] forKey:@"fields"];
 
   [self setClientId:123 configuration:config];
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   // Find all the FlutterTextInputViews we created.
   NSArray<FlutterTextInputView*>* inputFields = self.installedInputViews;
@@ -589,6 +617,7 @@ FLUTTER_ASSERT_ARC
   FlutterTextInputView* inactiveView = inputFields[1];
   [inactiveView replaceRange:[FlutterTextRange rangeWithNSRange:NSMakeRange(0, 0)]
                     withText:@"Autofilled!"];
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
 
   // Verify behavior.
   OCMVerify([engine updateEditingClient:0 withState:[OCMArg isNotNil] withTag:@"field2"]);
@@ -610,4 +639,61 @@ FLUTTER_ASSERT_ARC
   XCTAssertNotEqual([inputView performSelector:@selector(font)], nil);
 }
 
+- (void)testClearAutofillContextClearsSelection {
+  NSMutableDictionary* regularField = self.mutableTemplateCopy;
+  NSDictionary* editingValue = @{
+    @"text" : @"REGULAR_TEXT_FIELD",
+    @"composingBase" : @0,
+    @"composingExtent" : @3,
+    @"selectionBase" : @1,
+    @"selectionExtent" : @4
+  };
+  [regularField setValue:@{
+    @"uniqueIdentifier" : @"field2",
+    @"hints" : @[ @"hint2" ],
+    @"editingValue" : editingValue,
+  }
+                  forKey:@"autofill"];
+  [regularField addEntriesFromDictionary:editingValue];
+  [self setClientId:123 configuration:regularField];
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
+  XCTAssertEqual(self.installedInputViews.count, 1);
+
+  FlutterTextInputView* oldInputView = self.installedInputViews[0];
+  XCTAssert([oldInputView.text isEqualToString:@"REGULAR_TEXT_FIELD"]);
+  FlutterTextRange* selectionRange = (FlutterTextRange*)oldInputView.selectedTextRange;
+  XCTAssert(NSEqualRanges(selectionRange.range, NSMakeRange(1, 3)));
+
+  // Replace the original password field with new one. This should remove
+  // the old password field, but not immediately.
+  [self setClientId:124 configuration:self.mutablePasswordTemplateCopy];
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
+
+  XCTAssertEqual(self.installedInputViews.count, 2);
+
+  [textInputPlugin collectGarbageInputViews];
+  XCTAssertEqual(self.installedInputViews.count, 1);
+
+  // Verify the old input view is properly cleaned up.
+  XCTAssert([oldInputView.text isEqualToString:@""]);
+  selectionRange = (FlutterTextRange*)oldInputView.selectedTextRange;
+  XCTAssert(NSEqualRanges(selectionRange.range, NSMakeRange(0, 0)));
+}
+
+- (void)testGarbageInputViewsAreNotRemovedImmediately {
+  // Add a password field that should autofill.
+  [self setClientId:123 configuration:self.mutablePasswordTemplateCopy];
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
+
+  XCTAssertEqual(self.installedInputViews.count, 1);
+  // Add an input field that doesn't autofill. This should remove the password
+  // field, but not immediately.
+  [self setClientId:124 configuration:self.mutableTemplateCopy];
+  [self ensureOnlyActiveViewCanBecomeFirstResponder];
+
+  XCTAssertEqual(self.installedInputViews.count, 2);
+
+  [self commitAutofillContextAndVerify];
+}
+
 @end