[macos] expose runWithEngine constructor in FlutterViewController

Removing [engine setViewController:self]; because view is not loaded, but in that function controller is saved. Later, when the view is loaded (loadView) passed as an argument controller is checked against the saved controller and since they match, the nil view is not replaced with a new view.

Fixes: flutter/flutter#74735

engine/src/flutter/shell/platform/darwin/macos/framework/Headers/FlutterViewController.h

@@ -53,7 +53,18 @@ FLUTTER_DARWIN_EXPORT
                                  bundle:(nullable NSBundle*)nibBundleOrNil
     NS_DESIGNATED_INITIALIZER;
 - (nonnull instancetype)initWithCoder:(nonnull NSCoder*)nibNameOrNil NS_DESIGNATED_INITIALIZER;
-
+/**
+ * Initializes this FlutterViewController with the specified `FlutterEngine`.
+ *
+ * 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.
+ * @param nibBundle The NIB bundle.
+ */
+- (nonnull instancetype)initWithEngine:(nonnull FlutterEngine*)engine
+                               nibName:(nullable NSString*)nibName
+                                bundle:(nullable NSBundle*)nibBundle NS_DESIGNATED_INITIALIZER;
 /**
  * Invoked by the engine right before the engine is restarted.
  *

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

@@ -329,18 +329,21 @@ static void CommonInit(FlutterViewController* controller) {
                        nibName:(nullable NSString*)nibName
                         bundle:(nullable NSBundle*)nibBundle {
   NSAssert(engine != nil, @"Engine is required");
+  NSAssert(engine.viewController == nil,
+           @"The supplied FlutterEngine is already used with FlutterViewController "
+            "instance. One instance of the FlutterEngine can only be attached to one "
+            "FlutterViewController at a time. Set FlutterEngine.viewController "
+            "to nil before attaching it to another FlutterViewController.");
+
   self = [super initWithNibName:nibName bundle:nibBundle];
   if (self) {
-    if (engine.viewController) {
-      NSLog(@"The supplied FlutterEngine %@ is already used with FlutterViewController "
-             "instance %@. One instance of the FlutterEngine can only be attached to one "
-             "FlutterViewController at a time. Set FlutterEngine.viewController "
-             "to nil before attaching it to another FlutterViewController.",
-            [engine description], [engine.viewController description]);
-    }
     _engine = engine;
     CommonInit(self);
-    [engine setViewController:self];
+    if (engine.running) {
+      [self loadView];
+      engine.viewController = self;
+      [self initializeKeyboard];
+    }
   }
 
   return self;

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

@@ -23,6 +23,7 @@
 - (bool)testKeyboardIsRestartedOnEngineRestart;
 - (bool)testTrackpadGesturesAreSentToFramework;
 - (bool)testViewWillAppearCalledMultipleTimes;
+- (bool)testFlutterViewIsConfigured;
 
 + (void)respondFalseForSendEvent:(const FlutterKeyEvent&)event
                         callback:(nullable FlutterKeyEventCallback)callback
@@ -164,6 +165,10 @@ TEST(FlutterViewControllerTest, testViewWillAppearCalledMultipleTimes) {
   ASSERT_TRUE([[FlutterViewControllerTestObjC alloc] testViewWillAppearCalledMultipleTimes]);
 }
 
+TEST(FlutterViewControllerTest, testFlutterViewIsConfigured) {
+  ASSERT_TRUE([[FlutterViewControllerTestObjC alloc] testFlutterViewIsConfigured]);
+}
+
 }  // namespace flutter::testing
 
 @implementation FlutterViewControllerTestObjC
@@ -261,6 +266,27 @@ TEST(FlutterViewControllerTest, testViewWillAppearCalledMultipleTimes) {
   return true;
 }
 
+- (bool)testFlutterViewIsConfigured {
+  id engineMock = OCMClassMock([FlutterEngine class]);
+
+  id renderer_ = [[FlutterMetalRenderer alloc] initWithFlutterEngine:engineMock];
+  OCMStub([engineMock renderer]).andReturn(renderer_);
+
+  FlutterViewController* viewController = [[FlutterViewController alloc] initWithEngine:engineMock
+                                                                                nibName:@""
+                                                                                 bundle:nil];
+  [viewController loadView];
+
+  @try {
+    // Make sure "renderer" was called during "loadView", which means "flutterView" is created
+    OCMVerify([engineMock renderer]);
+  } @catch (...) {
+    return false;
+  }
+
+  return true;
+}
+
 - (bool)testFlagsChangedEventsArePropagatedIfNotHandled {
   id engineMock = OCMClassMock([FlutterEngine class]);
   id binaryMessengerMock = OCMProtocolMock(@protocol(FlutterBinaryMessenger));

engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterViewController_Internal.h

@@ -18,19 +18,6 @@
  */
 @property(nonatomic, readonly, nonnull) FlutterTextInputPlugin* textInputPlugin;
 
-/**
- * Initializes this FlutterViewController with the specified `FlutterEngine`.
- *
- * 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.
- * @param nibBundle The NIB bundle.
- */
-- (nonnull instancetype)initWithEngine:(nonnull FlutterEngine*)engine
-                               nibName:(nullable NSString*)nibName
-                                bundle:(nullable NSBundle*)nibBundle NS_DESIGNATED_INITIALIZER;
-
 /**
  * Returns YES if provided event is being currently redispatched by keyboard manager.
  */