Revert "[macOS] Formalize FlutterViewController's initialization flow…

…, and prohibit replacing (#38981)"

This reverts commit e3b2782.

shell/platform/darwin/macos/framework/Headers/FlutterEngine.h

@@ -7,8 +7,6 @@
 
 #import <Foundation/Foundation.h>
 
-#include <stdint.h>
-
 #import "FlutterBinaryMessenger.h"
 #import "FlutterDartProject.h"
 #import "FlutterMacros.h"
@@ -17,17 +15,6 @@
 
 // TODO: Merge this file with the iOS FlutterEngine.h.
 
-/**
- * The view ID for APIs that don't support multi-view.
- *
- * Some single-view APIs will eventually be replaced by their multi-view
- * variant. During the deprecation period, the single-view APIs will coexist with
- * and work with the multi-view APIs as if the other views don't exist.  For
- * backward compatibility, single-view APIs will always operate the view with
- * this ID. Also, the first view assigned to the engine will also have this ID.
- */
-extern const uint64_t kFlutterDefaultViewId;
-
 @class FlutterViewController;
 
 /**
@@ -80,15 +67,6 @@ FLUTTER_DARWIN_EXPORT
  *
  * The default view always has ID kFlutterDefaultViewId, and is the view
  * operated by the APIs that do not have a view ID specified.
- *
- * Setting this field from nil to a non-nil view controller also updates
- * the view controller's engine and ID.
- *
- * Setting this field from non-nil to nil will terminate the engine if
- * allowHeadlessExecution is NO.
- *
- * Setting this field from non-nil to a different non-nil FlutterViewController
- * is prohibited and will throw an assertion error.
  */
 @property(nonatomic, nullable, weak) FlutterViewController* viewController;
 

shell/platform/darwin/macos/framework/Headers/FlutterViewController.h

@@ -25,25 +25,6 @@ typedef NS_ENUM(NSInteger, FlutterMouseTrackingMode) {
 
 /**
  * Controls a view that displays Flutter content and manages input.
- *
- * A FlutterViewController works with a FlutterEngine. Upon creation, the view
- * controller is always added to an engine, either a given engine, or it implicitly
- * creates an engine and add itself to that engine.
- *
- * The FlutterEngine assigns each view controller attached to it a unique ID.
- * Each view controller corresponds to a view, and the ID is used by the framework
- * to specify which view to operate.
- *
- * A FlutterViewController can also be unattached to an engine after it is manually
- * unset from the engine, or transiently during the initialization process.
- * An unattached view controller is invalid. Whether the view controller is attached
- * can be queried using FlutterViewController#attached.
- *
- * The FlutterViewController strongly references the FlutterEngine, while
- * the engine weakly the view controller. When a FlutterViewController is deallocated,
- * it automatically removes itself from its attached engine. When a FlutterEngine
- * has no FlutterViewControllers attached, it might shut down itself or not depending
- * on its configuration.
  */
 FLUTTER_DARWIN_EXPORT
 @interface FlutterViewController : NSViewController <FlutterPluginRegistry>
@@ -53,16 +34,6 @@ FLUTTER_DARWIN_EXPORT
  */
 @property(nonatomic, nonnull, readonly) FlutterEngine* engine;
 
-/**
- * The identifier for this view controller.
- *
- * The ID is assigned by FlutterEngine when the view controller is attached.
- *
- * If the view controller is unattached (see FlutterViewController#attached),
- * reading this property throws an assertion.
- */
-@property(nonatomic, readonly) uint64_t id;
-
 /**
  * The style of mouse tracking to use for the view. Defaults to
  * FlutterMouseTrackingModeInKeyWindow.
@@ -72,12 +43,6 @@ FLUTTER_DARWIN_EXPORT
 /**
  * Initializes a controller that will run the given project.
  *
- * In this initializer, this controller creates an engine, and is attached to
- * that engine as the default controller. In this way, this controller can not
- * be set to other engines. This initializer is suitable for the first Flutter
- * view controller of the app. To use the controller with an existing engine,
- * use initWithEngine:nibName:bundle: instead.
- *
  * @param project The project to run in this view controller. If nil, a default `FlutterDartProject`
  *                will be used.
  */
@@ -91,8 +56,7 @@ FLUTTER_DARWIN_EXPORT
 /**
  * Initializes this FlutterViewController with the specified `FlutterEngine`.
  *
- * This initializer is suitable for both the first Flutter view controller and
- * the following ones of the app.
+ * The initialized viewcontroller will attach itself to the engine as part of this process.
  *
  * @param engine The `FlutterEngine` instance to attach to. Cannot be nil.
  * @param nibName The NIB name to initialize this controller with.
@@ -101,12 +65,6 @@ FLUTTER_DARWIN_EXPORT
 - (nonnull instancetype)initWithEngine:(nonnull FlutterEngine*)engine
                                nibName:(nullable NSString*)nibName
                                 bundle:(nullable NSBundle*)nibBundle NS_DESIGNATED_INITIALIZER;
-
-/**
- * Return YES if the view controller is attached to an engine.
- */
-- (BOOL)attached;
-
 /**
  * Invoked by the engine right before the engine is restarted.
  *

shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMacTest.mm

@@ -51,22 +51,26 @@ @implementation AccessibilityBridgeTestEngine
 namespace {
 
 // Returns an engine configured for the text fixture resource configuration.
-FlutterViewController* CreateTestViewController() {
+FlutterEngine* CreateTestEngine() {
   NSString* fixtures = @(testing::GetFixturesPath());
   FlutterDartProject* project = [[FlutterDartProject alloc]
       initWithAssetsPath:fixtures
              ICUDataPath:[fixtures stringByAppendingString:@"/icudtl.dat"]];
-  FlutterEngine* engine = [[AccessibilityBridgeTestEngine alloc] initWithName:@"test"
-                                                                      project:project
-                                                       allowHeadlessExecution:true];
-  return [[FlutterViewController alloc] initWithEngine:engine nibName:nil bundle:nil];
+  return [[AccessibilityBridgeTestEngine alloc] initWithName:@"test"
+                                                     project:project
+                                      allowHeadlessExecution:true];
 }
 }  // namespace
 
 TEST(AccessibilityBridgeMacTest, sendsAccessibilityCreateNotificationToWindowOfFlutterView) {
-  FlutterViewController* viewController = CreateTestViewController();
-  FlutterEngine* engine = viewController.engine;
+  FlutterEngine* engine = CreateTestEngine();
+  NSString* fixtures = @(testing::GetFixturesPath());
+  FlutterDartProject* project = [[FlutterDartProject alloc]
+      initWithAssetsPath:fixtures
+             ICUDataPath:[fixtures stringByAppendingString:@"/icudtl.dat"]];
+  FlutterViewController* viewController = [[FlutterViewController alloc] initWithProject:project];
   [viewController loadView];
+  [engine setViewController:viewController];
 
   NSWindow* expectedTarget = [[NSWindow alloc] initWithContentRect:NSMakeRect(0, 0, 800, 600)
                                                          styleMask:NSBorderlessWindowMask
@@ -118,9 +122,14 @@ @implementation AccessibilityBridgeTestEngine
 }
 
 TEST(AccessibilityBridgeMacTest, doesNotSendAccessibilityCreateNotificationWhenHeadless) {
-  FlutterViewController* viewController = CreateTestViewController();
-  FlutterEngine* engine = viewController.engine;
+  FlutterEngine* engine = CreateTestEngine();
+  NSString* fixtures = @(testing::GetFixturesPath());
+  FlutterDartProject* project = [[FlutterDartProject alloc]
+      initWithAssetsPath:fixtures
+             ICUDataPath:[fixtures stringByAppendingString:@"/icudtl.dat"]];
+  FlutterViewController* viewController = [[FlutterViewController alloc] initWithProject:project];
   [viewController loadView];
+  [engine setViewController:viewController];
   // Setting up bridge so that the AccessibilityBridgeMacDelegateSpy
   // can query semantics information from.
   engine.semanticsEnabled = YES;
@@ -164,9 +173,15 @@ @implementation AccessibilityBridgeTestEngine
 }
 
 TEST(AccessibilityBridgeMacTest, doesNotSendAccessibilityCreateNotificationWhenNoWindow) {
-  FlutterViewController* viewController = CreateTestViewController();
-  FlutterEngine* engine = viewController.engine;
+  FlutterEngine* engine = CreateTestEngine();
+  // Create a view controller without attaching it to a window.
+  NSString* fixtures = @(testing::GetFixturesPath());
+  FlutterDartProject* project = [[FlutterDartProject alloc]
+      initWithAssetsPath:fixtures
+             ICUDataPath:[fixtures stringByAppendingString:@"/icudtl.dat"]];
+  FlutterViewController* viewController = [[FlutterViewController alloc] initWithProject:project];
   [viewController loadView];
+  [engine setViewController:viewController];
 
   // Setting up bridge so that the AccessibilityBridgeMacDelegateSpy
   // can query semantics information from.

shell/platform/darwin/macos/framework/Source/FlutterCompositor.h

@@ -10,6 +10,7 @@
 
 #include "flutter/fml/macros.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterPlatformViewController.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterView.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewProvider.h"
 #include "flutter/shell/platform/embedder/embedder.h"
 

shell/platform/darwin/macos/framework/Source/FlutterEngine.mm

@@ -19,8 +19,6 @@
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProvider.h"
 #include "flutter/shell/platform/embedder/embedder.h"
 
-const uint64_t kFlutterDefaultViewId = 0;
-
 /**
  * Constructs and returns a FlutterLocale struct corresponding to |locale|, which must outlive
  * the returned struct.
@@ -82,8 +80,6 @@ @interface FlutterEngine () <FlutterBinaryMessenger>
  */
 @property(nonatomic, strong) NSMutableArray<NSNumber*>* isResponseValid;
 
-- (nullable FlutterViewController*)viewControllerForId:(uint64_t)viewId;
-
 /**
  * Sends the list of user-preferred locales to the Flutter engine.
  */
@@ -217,6 +213,8 @@ @implementation FlutterEngine {
   // when the engine is destroyed.
   std::unique_ptr<flutter::FlutterCompositor> _macOSCompositor;
 
+  FlutterViewEngineProvider* _viewProvider;
+
   // FlutterCompositor is copied and used in embedder.cc.
   FlutterCompositor _compositor;
 
@@ -250,6 +248,7 @@ - (instancetype)initWithName:(NSString*)labelPrefix
   _currentMessengerConnection = 1;
   _allowHeadlessExecution = allowHeadlessExecution;
   _semanticsEnabled = NO;
+  _viewProvider = [[FlutterViewEngineProvider alloc] initWithEngine:self];
   _isResponseValid = [[NSMutableArray alloc] initWithCapacity:1];
   [_isResponseValid addObject:@YES];
 
@@ -412,41 +411,29 @@ - (void)loadAOTData:(NSString*)assetsDir {
 }
 
 - (void)setViewController:(FlutterViewController*)controller {
-  if (_viewController == controller) {
-    // From nil to nil, or from non-nil to the same controller.
-    return;
-  }
-  if (_viewController == nil && controller != nil) {
-    // From nil to non-nil.
-    NSAssert(controller.engine == nil,
-             @"Failed to set view controller to the engine: "
-             @"The given FlutterViewController is already attached to an engine %@. "
-             @"If you wanted to create an FlutterViewController and set it to an existing engine, "
-             @"you should create it with init(engine:, nibName, bundle:) instead.",
-             controller.engine);
+  if (_viewController != controller) {
     _viewController = controller;
-    [_viewController attachToEngine:self withId:kFlutterDefaultViewId];
-  } else if (_viewController != nil && controller == nil) {
-    // From non-nil to nil.
-    [_viewController detachFromEngine];
-    _viewController = nil;
-    if (!_allowHeadlessExecution) {
+
+    if (_semanticsEnabled && _bridge) {
+      _bridge->UpdateDefaultViewController(_viewController);
+    }
+
+    if (!controller && !_allowHeadlessExecution) {
       [self shutDownEngine];
     }
-  } else {
-    // From non-nil to a different non-nil view controller.
-    NSAssert(NO,
-             @"Failed to set view controller to the engine: "
-             @"The engine already has a default view controller %@. "
-             @"If you wanted to make the default view render in a different window, "
-             @"you should attach the current view controller to the window instead.",
-             _viewController);
   }
 }
 
 - (FlutterCompositor*)createFlutterCompositor {
-  _macOSCompositor = std::make_unique<flutter::FlutterCompositor>(
-      [[FlutterViewEngineProvider alloc] initWithEngine:self], _platformViewController);
+  // TODO(richardjcai): Add support for creating a FlutterCompositor
+  // with a nil _viewController for headless engines.
+  // https://github.com/flutter/flutter/issues/71606
+  if (!_viewController) {
+    return nil;
+  }
+
+  _macOSCompositor =
+      std::make_unique<flutter::FlutterCompositor>(_viewProvider, _platformViewController);
 
   _compositor = {};
   _compositor.struct_size = sizeof(FlutterCompositor);
@@ -552,10 +539,10 @@ - (nonnull NSString*)executableName {
 }
 
 - (void)updateWindowMetrics {
-  if (!_engine || !self.viewController.viewLoaded) {
+  if (!_engine || !_viewController.viewLoaded) {
     return;
   }
-  NSView* view = self.viewController.flutterView;
+  NSView* view = _viewController.flutterView;
   CGRect scaledBounds = [view convertRectToBacking:view.bounds];
   CGSize scaledSize = scaledBounds.size;
   double pixelRatio = view.bounds.size.width == 0 ? 1 : scaledSize.width / view.bounds.size.width;
@@ -616,17 +603,6 @@ - (FlutterPlatformViewController*)platformViewController {
 
 #pragma mark - Private methods
 
-- (FlutterViewController*)viewControllerForId:(uint64_t)viewId {
-  // TODO(dkwingsmt): The engine only supports single-view, therefore it
-  // only processes the default ID. After the engine supports multiple views,
-  // this method should be able to return the view for any IDs.
-  NSAssert(viewId == kFlutterDefaultViewId, @"Unexpected view ID %llu", viewId);
-  if (viewId == kFlutterDefaultViewId) {
-    return _viewController;
-  }
-  return nil;
-}
-
 - (void)sendUserLocales {
   if (!self.running) {
     return;
@@ -703,7 +679,9 @@ - (void)shutDownEngine {
     return;
   }
 
-  [self.viewController.flutterView shutdown];
+  if (_viewController && _viewController.flutterView) {
+    [_viewController.flutterView shutdown];
+  }
 
   FlutterEngineResult result = _embedderAPI.Deinitialize(_engine);
   if (result != kSuccess) {