Add focus support for platform view (flutter/engine#33093)

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

@@ -991,6 +991,36 @@ static void SetEntryPoint(flutter::Settings* settings, NSString* entrypoint, NSS
                               arguments:@[ @(client) ]];
 }
 
+- (void)flutterTextInputViewDidResignFirstResponder:(FlutterTextInputView*)textInputView {
+  // Platform view's first responder detection logic:
+  //
+  // All text input widgets (e.g. EditableText) are backed by a dummy UITextInput view
+  // in the TextInputPlugin. When this dummy UITextInput view resigns first responder,
+  // check if any platform view becomes first responder. If any platform view becomes
+  // first responder, send a "viewFocused" channel message to inform the framework to un-focus
+  // the previously focused text input.
+  //
+  // Caveat:
+  // 1. This detection logic does not cover the scenario when a platform view becomes
+  // first responder without any flutter text input resigning its first responder status
+  // (e.g. user tapping on platform view first). For now it works fine because the TextInputPlugin
+  // does not track the focused platform view id (which is different from Android implementation).
+  //
+  // 2. This detection logic assumes that all text input widgets are backed by a dummy
+  // UITextInput view in the TextInputPlugin, which may not hold true in the future.
+
+  // Have to check in the next run loop, because iOS requests the previous first responder to
+  // resign before requesting the next view to become first responder.
+  dispatch_async(dispatch_get_main_queue(), ^(void) {
+    long platform_view_id = self.platformViewsController->FindFirstResponderPlatformViewId();
+    if (platform_view_id == -1) {
+      return;
+    }
+
+    [_platformViewsChannel.get() invokeMethod:@"viewFocused" arguments:@(platform_view_id)];
+  });
+}
+
 #pragma mark - Undo Manager Delegate
 
 - (void)flutterUndoManagerPlugin:(FlutterUndoManagerPlugin*)undoManagerPlugin

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

@@ -19,6 +19,20 @@
 #import "flutter/shell/platform/darwin/ios/ios_surface.h"
 #import "flutter/shell/platform/darwin/ios/ios_surface_gl.h"
 
+@implementation UIView (FirstResponder)
+- (BOOL)flt_hasFirstResponderInViewHierarchySubtree {
+  if (self.isFirstResponder) {
+    return YES;
+  }
+  for (UIView* subview in self.subviews) {
+    if (subview.flt_hasFirstResponderInViewHierarchySubtree) {
+      return YES;
+    }
+  }
+  return NO;
+}
+@end
+
 namespace flutter {
 
 std::shared_ptr<FlutterPlatformViewLayer> FlutterPlatformViewLayerPool::GetLayer(
@@ -328,6 +342,15 @@ UIView* FlutterPlatformViewsController::GetPlatformViewByID(int view_id) {
   return [touch_interceptors_[view_id].get() embeddedView];
 }
 
+long FlutterPlatformViewsController::FindFirstResponderPlatformViewId() {
+  for (auto const& [id, root_view] : root_views_) {
+    if ((UIView*)(root_view.get()).flt_hasFirstResponderInViewHierarchySubtree) {
+      return id;
+    }
+  }
+  return -1;
+}
+
 std::vector<SkCanvas*> FlutterPlatformViewsController::GetCurrentCanvases() {
   std::vector<SkCanvas*> canvases;
   for (size_t i = 0; i < composition_order_.size(); i++) {

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

@@ -1105,4 +1105,36 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(std::string name) {
   return pixel[3];
 }
 
+- (void)testHasFirstResponderInViewHierarchySubtree_viewItselfBecomesFirstResponder {
+  // For view to become the first responder, it must be a descendant of a UIWindow
+  UIWindow* window = [[UIWindow alloc] init];
+  UITextField* textField = [[UITextField alloc] init];
+  [window addSubview:textField];
+
+  [textField becomeFirstResponder];
+  XCTAssertTrue(textField.isFirstResponder);
+  XCTAssertTrue(textField.flt_hasFirstResponderInViewHierarchySubtree);
+  [textField resignFirstResponder];
+  XCTAssertFalse(textField.isFirstResponder);
+  XCTAssertFalse(textField.flt_hasFirstResponderInViewHierarchySubtree);
+}
+
+- (void)testHasFirstResponderInViewHierarchySubtree_descendantViewBecomesFirstResponder {
+  // For view to become the first responder, it must be a descendant of a UIWindow
+  UIWindow* window = [[UIWindow alloc] init];
+  UIView* view = [[UIView alloc] init];
+  UIView* childView = [[UIView alloc] init];
+  UITextField* textField = [[UITextField alloc] init];
+  [window addSubview:view];
+  [view addSubview:childView];
+  [childView addSubview:textField];
+
+  [textField becomeFirstResponder];
+  XCTAssertTrue(textField.isFirstResponder);
+  XCTAssertTrue(view.flt_hasFirstResponderInViewHierarchySubtree);
+  [textField resignFirstResponder];
+  XCTAssertFalse(textField.isFirstResponder);
+  XCTAssertFalse(view.flt_hasFirstResponderInViewHierarchySubtree);
+}
+
 @end

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -177,6 +177,10 @@ class FlutterPlatformViewsController {
 
   void OnMethodCall(FlutterMethodCall* call, FlutterResult& result);
 
+  // Returns the platform view id if the platform view (or any of its descendant view) is the first
+  // responder. Returns -1 if no such platform view is found.
+  long FindFirstResponderPlatformViewId();
+
  private:
   static const size_t kMaxLayerAllocations = 2;
 
@@ -329,4 +333,9 @@ class FlutterPlatformViewsController {
 - (UIView*)embeddedView;
 @end
 
+@interface UIView (FirstResponder)
+// Returns YES if a view or any of its descendant view is the first responder. Returns NO otherwise.
+@property(nonatomic, readonly) BOOL flt_hasFirstResponderInViewHierarchySubtree;
+@end
+
 #endif  // FLUTTER_SHELL_PLATFORM_DARWIN_IOS_FRAMEWORK_SOURCE_FLUTTERPLATFORMVIEWS_INTERNAL_H_

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputDelegate.h

@@ -59,6 +59,7 @@ typedef NS_ENUM(NSInteger, FlutterFloatingCursorDragState) {
     insertTextPlaceholderWithSize:(CGSize)size
                        withClient:(int)client;
 - (void)flutterTextInputView:(FlutterTextInputView*)textInputView removeTextPlaceholder:(int)client;
+- (void)flutterTextInputViewDidResignFirstResponder:(FlutterTextInputView*)textInputView;
 
 @end
 

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

@@ -39,6 +39,7 @@ const CGRect kSpacePanBounds = {{-2500, -2500}, {5000, 5000}};
 static NSString* const kShowMethod = @"TextInput.show";
 static NSString* const kHideMethod = @"TextInput.hide";
 static NSString* const kSetClientMethod = @"TextInput.setClient";
+static NSString* const kSetPlatformViewClientMethod = @"TextInput.setPlatformViewClient";
 static NSString* const kSetEditingStateMethod = @"TextInput.setEditingState";
 static NSString* const kClearClientMethod = @"TextInput.clearClient";
 static NSString* const kSetEditableSizeAndTransformMethod =
@@ -1075,6 +1076,14 @@ static BOOL IsSelectionRectCloserToPoint(CGPoint point,
   return _textInputClient != 0;
 }
 
+- (BOOL)resignFirstResponder {
+  BOOL success = [super resignFirstResponder];
+  if (success) {
+    [self.textInputDelegate flutterTextInputViewDidResignFirstResponder:self];
+  }
+  return success;
+}
+
 - (BOOL)canPerformAction:(SEL)action withSender:(id)sender {
   // When scribble is available, the FlutterTextInputView will display the native toolbar unless
   // these text editing actions are disabled.
@@ -2071,6 +2080,10 @@ static BOOL IsSelectionRectCloserToPoint(CGPoint point,
   } else if ([method isEqualToString:kSetClientMethod]) {
     [self setTextInputClient:[args[0] intValue] withConfiguration:args[1]];
     result(nil);
+  } else if ([method isEqualToString:kSetPlatformViewClientMethod]) {
+    // This method call has a `platformViewId` argument, but we do not need it for iOS for now.
+    [self setPlatformViewTextInputClient];
+    result(nil);
   } else if ([method isEqualToString:kSetEditingStateMethod]) {
     [self setTextInputEditingState:args];
     result(nil);
@@ -2187,6 +2200,16 @@ static BOOL IsSelectionRectCloserToPoint(CGPoint point,
   [self addToInputParentViewIfNeeded:_activeView];
 }
 
+- (void)setPlatformViewTextInputClient {
+  // No need to track the platformViewID (unlike in Android). When a platform view
+  // becomes the first responder, simply hide this dummy text input view (`_activeView`)
+  // for the previously focused widget.
+  [self removeEnableFlutterTextInputViewAccessibilityTimer];
+  _activeView.accessibilityEnabled = NO;
+  [_activeView removeFromSuperview];
+  [_inputHider removeFromSuperview];
+}
+
 - (void)setTextInputClient:(int)client withConfiguration:(NSDictionary*)configuration {
   [self resetAllClientIds];
   // Hide all input views from autofill, only make those in the new configuration visible

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

@@ -88,7 +88,7 @@ FLUTTER_ASSERT_ARC
 
   textInputPlugin = [[FlutterTextInputPlugin alloc] initWithDelegate:engine];
 
-  viewController = [FlutterViewController new];
+  viewController = [[FlutterViewController alloc] init];
   textInputPlugin.viewController = viewController;
 
   // Clear pasteboard between tests.
@@ -167,7 +167,7 @@ FLUTTER_ASSERT_ARC
 #pragma mark - Tests
 - (void)testNoDanglingEnginePointer {
   __weak FlutterTextInputPlugin* weakFlutterTextInputPlugin;
-  FlutterViewController* flutterViewController = [FlutterViewController new];
+  FlutterViewController* flutterViewController = [[FlutterViewController alloc] init];
   __weak FlutterEngine* weakFlutterEngine;
 
   FlutterTextInputView* currentView;
@@ -1825,7 +1825,7 @@ FLUTTER_ASSERT_ARC
 }
 
 - (void)testFlutterTextInputPluginRetainsFlutterTextInputView {
-  FlutterViewController* flutterViewController = [FlutterViewController new];
+  FlutterViewController* flutterViewController = [[FlutterViewController alloc] init];
   FlutterTextInputPlugin* myInputPlugin = [[FlutterTextInputPlugin alloc] initWithDelegate:engine];
   myInputPlugin.viewController = flutterViewController;
 
@@ -1858,7 +1858,7 @@ FLUTTER_ASSERT_ARC
 }
 
 - (void)testFlutterTextInputPluginHostViewNotNil {
-  FlutterViewController* flutterViewController = [FlutterViewController new];
+  FlutterViewController* flutterViewController = [[FlutterViewController alloc] init];
   FlutterEngine* flutterEngine = [[FlutterEngine alloc] init];
   [flutterEngine runWithEntrypoint:nil];
   flutterEngine.viewController = flutterViewController;
@@ -1866,4 +1866,26 @@ FLUTTER_ASSERT_ARC
   XCTAssertNotNil([flutterEngine.textInputPlugin hostView]);
 }
 
+- (void)testSetPlatformViewClient {
+  FlutterViewController* flutterViewController = [[FlutterViewController alloc] init];
+  FlutterTextInputPlugin* myInputPlugin = [[FlutterTextInputPlugin alloc] initWithDelegate:engine];
+  myInputPlugin.viewController = flutterViewController;
+
+  FlutterMethodCall* setClientCall = [FlutterMethodCall
+      methodCallWithMethodName:@"TextInput.setClient"
+                     arguments:@[ [NSNumber numberWithInt:123], self.mutablePasswordTemplateCopy ]];
+  [myInputPlugin handleMethodCall:setClientCall
+                           result:^(id _Nullable result){
+                           }];
+  UIView* activeView = myInputPlugin.textInputView;
+  XCTAssertNotNil(activeView.superview, @"activeView must be added to the view hierarchy.");
+  FlutterMethodCall* setPlatformViewClientCall = [FlutterMethodCall
+      methodCallWithMethodName:@"TextInput.setPlatformViewClient"
+                     arguments:@{@"platformViewId" : [NSNumber numberWithLong:456]}];
+  [myInputPlugin handleMethodCall:setPlatformViewClientCall
+                           result:^(id _Nullable result){
+                           }];
+  XCTAssertNil(activeView.superview, @"activeView must be removed from view hierarchy.");
+}
+
 @end