macOS: add stubs for PlatformView gesture handling (flutter/engine#50630)

Adds method handler stubs for acceptGesture and rejectGesture channel method invocations. This avoids error messages being logged and puts in place the scaffolding for the implementation.

Issue: https://github.com/flutter/flutter/issues/124492

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

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

@@ -116,11 +116,45 @@
     NSNumber* arg = [call arguments];
     int64_t viewId = [arg longLongValue];
     [self onDisposeWithViewID:viewId result:result];
+  } else if ([[call method] isEqualToString:@"acceptGesture"]) {
+    [self handleAcceptGesture:call result:result];
+  } else if ([[call method] isEqualToString:@"rejectGesture"]) {
+    [self handleRejectGesture:call result:result];
   } else {
     result(FlutterMethodNotImplemented);
   }
 }
 
+- (void)handleAcceptGesture:(FlutterMethodCall*)call result:(FlutterResult)result {
+  NSDictionary<NSString*, id>* args = [call arguments];
+  NSAssert(args && args[@"id"], @"id argument is required");
+  int64_t viewId = [args[@"id"] longLongValue];
+  if (_platformViews.count(viewId) == 0) {
+    result([FlutterError errorWithCode:@"unknown_view"
+                               message:@"trying to set gesture state for an unknown view"
+                               details:[NSString stringWithFormat:@"view id: '%lld'", viewId]]);
+    return;
+  }
+
+  // TODO(cbracken): Implement. https://github.com/flutter/flutter/issues/124492
+  result(nil);
+}
+
+- (void)handleRejectGesture:(FlutterMethodCall*)call result:(FlutterResult)result {
+  NSDictionary<NSString*, id>* args = [call arguments];
+  NSAssert(args && args[@"id"], @"id argument is required");
+  int64_t viewId = [args[@"id"] longLongValue];
+  if (_platformViews.count(viewId) == 0) {
+    result([FlutterError errorWithCode:@"unknown_view"
+                               message:@"trying to set gesture state for an unknown view"
+                               details:[NSString stringWithFormat:@"view id: '%lld'", viewId]]);
+    return;
+  }
+
+  // TODO(cbracken): Implement. https://github.com/flutter/flutter/issues/124492
+  result(nil);
+}
+
 - (void)disposePlatformViews {
   if (_platformViewsToDispose.empty()) {
     return;

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

@@ -161,4 +161,120 @@ TEST(FlutterPlatformViewController, TestDisposeOnMissingViewId) {
   EXPECT_TRUE(errored);
 }
 
+TEST(FlutterPlatformViewController, TestAcceptGesture) {
+  FlutterPlatformViewController* platformViewController =
+      [[FlutterPlatformViewController alloc] init];
+  [platformViewController registerViewFactory:[TestFlutterPlatformViewFactory alloc]
+                                       withId:@"MockPlatformView"];
+
+  // Create the PlatformView.
+  const NSNumber* viewId = [NSNumber numberWithLongLong:2];
+  FlutterMethodCall* methodCallOnCreate = [FlutterMethodCall
+      methodCallWithMethodName:@"create"
+                     arguments:@{@"id" : viewId, @"viewType" : @"MockPlatformView"}];
+  __block bool created = false;
+  FlutterResult resultOnCreate = ^(id result) {
+    // If a platform view is successfully created, the result is nil.
+    if (result == nil) {
+      created = true;
+    }
+  };
+  [platformViewController handleMethodCall:methodCallOnCreate result:resultOnCreate];
+
+  // Call acceptGesture.
+  FlutterMethodCall* methodCallAcceptGesture =
+      [FlutterMethodCall methodCallWithMethodName:@"acceptGesture" arguments:@{@"id" : viewId}];
+  __block bool acceptGestureCalled = false;
+  FlutterResult resultAcceptGesture = ^(id result) {
+    // If a acceptGesture is successful, the result is nil.
+    if (result == nil) {
+      acceptGestureCalled = true;
+    }
+  };
+  [platformViewController handleMethodCall:methodCallAcceptGesture result:resultAcceptGesture];
+
+  EXPECT_TRUE(created);
+  EXPECT_TRUE(acceptGestureCalled);
+}
+
+TEST(FlutterPlatformViewController, TestAcceptGestureOnMissingViewId) {
+  FlutterPlatformViewController* platformViewController =
+      [[FlutterPlatformViewController alloc] init];
+  [platformViewController registerViewFactory:[TestFlutterPlatformViewFactory alloc]
+                                       withId:@"MockPlatformView"];
+
+  // Call rejectGesture.
+  FlutterMethodCall* methodCallAcceptGesture =
+      [FlutterMethodCall methodCallWithMethodName:@"acceptGesture" arguments:@{
+        @"id" : @20
+      }];
+  __block bool errored = false;
+  FlutterResult result = ^(id result) {
+    if ([result isKindOfClass:[FlutterError class]]) {
+      errored = true;
+    }
+  };
+  [platformViewController handleMethodCall:methodCallAcceptGesture result:result];
+
+  EXPECT_TRUE(errored);
+}
+
+TEST(FlutterPlatformViewController, TestRejectGesture) {
+  FlutterPlatformViewController* platformViewController =
+      [[FlutterPlatformViewController alloc] init];
+  [platformViewController registerViewFactory:[TestFlutterPlatformViewFactory alloc]
+                                       withId:@"MockPlatformView"];
+
+  // Create the PlatformView.
+  const NSNumber* viewId = [NSNumber numberWithLongLong:2];
+  FlutterMethodCall* methodCallOnCreate = [FlutterMethodCall
+      methodCallWithMethodName:@"create"
+                     arguments:@{@"id" : viewId, @"viewType" : @"MockPlatformView"}];
+  __block bool created = false;
+  FlutterResult resultOnCreate = ^(id result) {
+    // If a platform view is successfully created, the result is nil.
+    if (result == nil) {
+      created = true;
+    }
+  };
+  [platformViewController handleMethodCall:methodCallOnCreate result:resultOnCreate];
+
+  // Call rejectGesture.
+  FlutterMethodCall* methodCallRejectGesture =
+      [FlutterMethodCall methodCallWithMethodName:@"rejectGesture" arguments:@{@"id" : viewId}];
+  __block bool rejectGestureCalled = false;
+  FlutterResult resultRejectGesture = ^(id result) {
+    // If a rejectGesture is successful, the result is nil.
+    if (result == nil) {
+      rejectGestureCalled = true;
+    }
+  };
+  [platformViewController handleMethodCall:methodCallRejectGesture result:resultRejectGesture];
+
+  EXPECT_TRUE(created);
+  EXPECT_TRUE(rejectGestureCalled);
+}
+
+TEST(FlutterPlatformViewController, TestRejectGestureOnMissingViewId) {
+  FlutterPlatformViewController* platformViewController =
+      [[FlutterPlatformViewController alloc] init];
+  [platformViewController registerViewFactory:[TestFlutterPlatformViewFactory alloc]
+                                       withId:@"MockPlatformView"];
+
+  // Call rejectGesture.
+  FlutterMethodCall* methodCallRejectGesture =
+      [FlutterMethodCall methodCallWithMethodName:@"rejectGesture" arguments:@{
+        @"id" : @20
+      }];
+  __block bool errored = false;
+  FlutterResult result = ^(id result) {
+    if ([result isKindOfClass:[FlutterError class]]) {
+      errored = true;
+    }
+  };
+  [platformViewController handleMethodCall:methodCallRejectGesture result:result];
+
+  EXPECT_TRUE(errored);
+}
+
 }  // namespace flutter::testing