Migrate Event class (#49887)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49887

## Changelog:
[Internal] -

As in the title.

This was the last Java file in the `events-common` module, so now it can be a pure Kotlin one.

NOTE: I opted to make the base method `Event.getEventData` public (instead of previously protected), as based on the usage patterns by the users this seems to make the most sense in this context.

Reviewed By: cortinico

Differential Revision: D70777597

fbshipit-source-id: fdaa52e4400ad8e86a8711daf359eb5a10974d05

packages/react-native/ReactAndroid/api/ReactAndroid.api

@@ -5036,6 +5036,7 @@ public abstract class com/facebook/react/uimanager/events/Event {
 	public fun coalesce (Lcom/facebook/react/uimanager/events/Event;)Lcom/facebook/react/uimanager/events/Event;
 	public fun dispatch (Lcom/facebook/react/uimanager/events/RCTEventEmitter;)V
 	public fun dispatchModern (Lcom/facebook/react/uimanager/events/RCTModernEventEmitter;)V
+	public final fun dispose ()V
 	protected fun experimental_isSynchronous ()Z
 	public fun getCoalescingKey ()S
 	public fun getEventAnimationDriverMatchSpec ()Lcom/facebook/react/uimanager/events/Event$EventAnimationDriverMatchSpec;
@@ -5044,11 +5045,12 @@ public abstract class com/facebook/react/uimanager/events/Event {
 	public abstract fun getEventName ()Ljava/lang/String;
 	public final fun getSurfaceId ()I
 	public final fun getTimestampMs ()J
-	public fun getUniqueID ()I
+	public final fun getUniqueID ()I
 	public final fun getViewTag ()I
-	protected fun init (I)V
-	protected fun init (II)V
-	protected fun init (IIJ)V
+	protected final fun init (I)V
+	protected final fun init (II)V
+	protected final fun init (IIJ)V
+	public final fun isInitialized ()Z
 	public fun onDispose ()V
 }
 

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/animated/NativeAnimatedNodesManager.kt

@@ -515,7 +515,7 @@ public class NativeAnimatedNodesManager(
     var foundAtLeastOneDriver = false
     val matchSpec = event.eventAnimationDriverMatchSpec
     for (driver in eventDrivers) {
-      if (matchSpec.match(driver.viewTag, driver.eventName)) {
+      if (matchSpec != null && matchSpec.match(driver.viewTag, driver.eventName)) {
         foundAtLeastOneDriver = true
         stopAnimationsForNode(driver.valueNode)
         event.dispatchModern(driver)

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactAccessibilityDelegate.java

@@ -323,7 +323,7 @@ public class ReactAccessibilityDelegate extends ExploreByTouchHelper {
                 }
 
                 @Override
-                protected WritableMap getEventData() {
+                public WritableMap getEventData() {
                   return event;
                 }
               });

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/BlackHoleEventDispatcher.kt

@@ -17,7 +17,7 @@ internal object BlackHoleEventDispatcher : EventDispatcher {
   override fun dispatchEvent(event: Event<*>) {
     FLog.d(
         "BlackHoleEventDispatcher",
-        "Trying to emit event to JS, but the React instance isn't ready. Event: ${event.eventName}")
+        "Trying to emit event to JS, but the React instance isn't ready. Event: ${event.getEventName()}")
   }
 
   override fun dispatchAllEvents(): Unit = Unit

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/Event.java

@@ -1,220 +0,0 @@
-/*
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-package com.facebook.react.uimanager.events;
-
-import androidx.annotation.Nullable;
-import com.facebook.infer.annotation.Nullsafe;
-import com.facebook.react.bridge.WritableMap;
-import com.facebook.react.common.SystemClock;
-
-/**
- * A UI event that can be dispatched to JS.
- *
- * <p>For dispatching events {@code getEventData} should be used. Once event object is passed to the
- * EventDispatched it should no longer be used as EventDispatcher may decide to recycle that object
- * (by calling {@link #dispose}).
- *
- * <p>If you need advanced customizations and overriding only {@code getEventData} doesn't work for
- * you, you must override both {@code dispatch} and {@code dispatchModern}. Both of these will be
- * deleted in the distant future and it is highly recommended to use only {@code getEventData}.
- *
- * <p>Old, pre-Fabric Events only used viewTag as the identifier, but Fabric needs surfaceId as well
- * as viewTag. You may use {@code UIManagerHelper.getSurfaceId} on a Fabric-managed View to get the
- * surfaceId. Fabric will work without surfaceId - making {@code Event} backwards-compatible - but
- * Events without SurfaceId are slightly slower to propagate.
- */
-@Nullsafe(Nullsafe.Mode.LOCAL)
-public abstract class Event<T extends Event> {
-
-  private static int sUniqueID = 0;
-
-  private boolean mInitialized;
-  private int mSurfaceId;
-  private int mViewTag;
-  private long mTimestampMs;
-  private int mUniqueID = sUniqueID++;
-  private @Nullable EventAnimationDriverMatchSpec mEventAnimationDriverMatchSpec;
-
-  protected Event() {}
-
-  @Deprecated
-  protected Event(int viewTag) {
-    init(viewTag);
-  }
-
-  protected Event(int surfaceId, int viewTag) {
-    init(surfaceId, viewTag);
-  }
-
-  @Deprecated
-  protected void init(int viewTag) {
-    init(-1, viewTag);
-  }
-
-  protected void init(int surfaceId, int viewTag) {
-    init(surfaceId, viewTag, SystemClock.uptimeMillis());
-  }
-
-  /**
-   * This method needs to be called before event is sent to event dispatcher. Event timestamps can
-   * optionally be dated/backdated to a custom time: for example, touch events should be dated with
-   * the system event time.
-   */
-  protected void init(int surfaceId, int viewTag, long timestampMs) {
-    mSurfaceId = surfaceId;
-    mViewTag = viewTag;
-    mTimestampMs = timestampMs;
-    mInitialized = true;
-  }
-
-  /**
-   * @return the view id for the view that generated this event
-   */
-  public final int getViewTag() {
-    return mViewTag;
-  }
-
-  /**
-   * @return the surfaceId for the view that generated this event
-   */
-  public final int getSurfaceId() {
-    return mSurfaceId;
-  }
-
-  /**
-   * @return the time at which the event happened in the {@link android.os.SystemClock#uptimeMillis}
-   *     base.
-   */
-  public final long getTimestampMs() {
-    return mTimestampMs;
-  }
-
-  /**
-   * @return false if this Event can *never* be coalesced
-   */
-  public boolean canCoalesce() {
-    return true;
-  }
-
-  /**
-   * Given two events, coalesce them into a single event that will be sent to JS instead of two
-   * separate events. By default, just chooses the one the is more recent, or {@code this} if
-   * timestamps are the same.
-   *
-   * <p>Two events will only ever try to be coalesced if they have the same event name, view id, and
-   * coalescing key.
-   */
-  public T coalesce(T otherEvent) {
-    return (T) (getTimestampMs() >= otherEvent.getTimestampMs() ? this : otherEvent);
-  }
-
-  /**
-   * @return a key used to determine which other events of this type this event can be coalesced
-   *     with. For example, touch move events should only be coalesced within a single gesture so a
-   *     coalescing key there would be the unique gesture id.
-   */
-  public short getCoalescingKey() {
-    return 0;
-  }
-
-  /**
-   * @return The unique id of this event.
-   */
-  public int getUniqueID() {
-    return mUniqueID;
-  }
-
-  /**
-   * Called when the EventDispatcher is done with an event, either because it was dispatched or
-   * because it was coalesced with another Event.
-   */
-  public void onDispose() {}
-
-  /*package*/ boolean isInitialized() {
-    return mInitialized;
-  }
-
-  /*package*/ final void dispose() {
-    mInitialized = false;
-    onDispose();
-  }
-
-  /**
-   * @return the name of this event as registered in JS
-   */
-  public abstract String getEventName();
-
-  public EventAnimationDriverMatchSpec getEventAnimationDriverMatchSpec() {
-    if (mEventAnimationDriverMatchSpec == null) {
-      mEventAnimationDriverMatchSpec =
-          new EventAnimationDriverMatchSpec() {
-            @Override
-            public boolean match(int viewTag, String eventName) {
-              return viewTag == getViewTag() && eventName.equals(getEventName());
-            }
-            ;
-          };
-    }
-    return mEventAnimationDriverMatchSpec;
-  }
-
-  /**
-   * Dispatch this event to JS using the given event emitter. Compatible with old and new renderer.
-   * Instead of using this or dispatchModern, it is recommended that you simply override
-   * `getEventData`.
-   */
-  @Deprecated
-  public void dispatch(RCTEventEmitter rctEventEmitter) {
-    rctEventEmitter.receiveEvent(getViewTag(), getEventName(), getEventData());
-  }
-
-  /** Can be overridden by classes when no custom logic for dispatching is needed. */
-  @Nullable
-  protected WritableMap getEventData() {
-    return null;
-  }
-
-  @EventCategoryDef
-  protected int getEventCategory() {
-    return EventCategoryDef.UNSPECIFIED;
-  }
-
-  protected boolean experimental_isSynchronous() {
-    return false;
-  }
-
-  /**
-   * Dispatch this event to JS using a V2 EventEmitter. If surfaceId is not -1 and `getEventData` is
-   * non-null, this will use the RCTModernEventEmitter API. Otherwise, it falls back to the
-   * old-style dispatch function. For Event classes that need to do something different, this method
-   * can always be overridden entirely, but it is not recommended.
-   *
-   * <p>This method additionally allows C++ to coalesce events and detect continuous ones for
-   * concurrent mode (Fabric only).
-   *
-   * @see #dispatch
-   */
-  public void dispatchModern(RCTModernEventEmitter rctEventEmitter) {
-    if (getSurfaceId() != -1) {
-      rctEventEmitter.receiveEvent(
-          getSurfaceId(),
-          getViewTag(),
-          getEventName(),
-          canCoalesce(),
-          getCoalescingKey(),
-          getEventData(),
-          getEventCategory());
-    } else {
-      dispatch(rctEventEmitter);
-    }
-  }
-
-  public interface EventAnimationDriverMatchSpec {
-    boolean match(int viewTag, String eventName);
-  }
-}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/Event.kt

@@ -0,0 +1,201 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+@file:Suppress("DEPRECATION")
+
+package com.facebook.react.uimanager.events
+
+import com.facebook.react.bridge.WritableMap
+import com.facebook.react.common.SystemClock.uptimeMillis
+
+/**
+ * A UI event that can be dispatched to JS.
+ *
+ * For dispatching events `getEventData` should be used. Once event object is passed to the
+ * EventDispatcher it should no longer be used as EventDispatcher may decide to recycle that object
+ * (by calling [dispose]).
+ *
+ * If you need advanced customizations and overriding only `getEventData` doesn't work for you, you
+ * must override both `dispatch` and `dispatchModern`. Both of these will be deleted in the distant
+ * future and it is highly recommended to use only `getEventData`.
+ *
+ * Old, pre-Fabric Events only used viewTag as the identifier, but Fabric needs surfaceId as well as
+ * viewTag. You may use [UIManagerHelper.getSurfaceId] on a Fabric-managed View to get the
+ * surfaceId. Fabric will work without surfaceId - making [Event] backwards-compatible - but Events
+ * without SurfaceId are slightly slower to propagate.
+ */
+public abstract class Event<T : Event<T>> {
+  public var isInitialized: Boolean = false
+    private set
+
+  /** @return the surfaceId for the view that generated this event */
+  public var surfaceId: Int = 0
+    private set
+
+  /** @return the view id for the view that generated this event */
+  public var viewTag: Int = 0
+    private set
+
+  /**
+   * @return the time at which the event happened in the [android.os.SystemClock.uptimeMillis] base.
+   */
+  public var timestampMs: Long = 0
+    private set
+
+  /** @return The unique id of this event. */
+  public val uniqueID: Int = uniqueIdCounter++
+  private var eventAnimationDriverMatchSpecCached: EventAnimationDriverMatchSpec? = null
+
+  protected constructor()
+
+  @Deprecated("Use constructor with explicit surfaceId instead")
+  protected constructor(viewTag: Int) {
+    init(viewTag)
+  }
+
+  protected constructor(surfaceId: Int, viewTag: Int) {
+    init(surfaceId, viewTag)
+  }
+
+  @Deprecated("Use version with explicit surfaceId instead")
+  protected fun init(viewTag: Int) {
+    init(-1, viewTag)
+  }
+
+  /**
+   * This method needs to be called before event is sent to event dispatcher. Event timestamps can
+   * optionally be dated/backdated to a custom time: for example, touch events should be dated with
+   * the system event time.
+   */
+  protected fun init(surfaceId: Int, viewTag: Int, timestampMs: Long) {
+    this.surfaceId = surfaceId
+    this.viewTag = viewTag
+    this.timestampMs = timestampMs
+    this.isInitialized = true
+  }
+
+  protected fun init(surfaceId: Int, viewTag: Int) {
+    init(surfaceId, viewTag, uptimeMillis())
+  }
+
+  /** @return false if this Event can *never* be coalesced */
+  public open fun canCoalesce(): Boolean = true
+
+  /**
+   * Given two events, coalesce them into a single event that will be sent to JS instead of two
+   * separate events. By default, just chooses the one the is more recent, or `this` if timestamps
+   * are the same.
+   *
+   * Two events will only ever try to be coalesced if they have the same event name, view id, and
+   * coalescing key.
+   */
+  public open fun coalesce(otherEvent: Event<T>?): Event<T>? =
+      if (timestampMs >= otherEvent?.timestampMs ?: 0) this else otherEvent
+
+  /**
+   * @return a key used to determine which other events of this type this event can be coalesced
+   *   with. For example, touch move events should only be coalesced within a single gesture so a
+   *   coalescing key there would be the unique gesture id.
+   */
+  public open fun getCoalescingKey(): Short = 0
+
+  /**
+   * Called when the EventDispatcher is done with an event, either because it was dispatched or
+   * because it was coalesced with another Event.
+   */
+  public open fun onDispose(): Unit = Unit
+
+  public fun dispose() {
+    this.isInitialized = false
+    onDispose()
+  }
+
+  /** @return the name of this event as registered in JS */
+  public abstract fun getEventName(): String
+
+  public open val eventAnimationDriverMatchSpec: EventAnimationDriverMatchSpec?
+    get() {
+      if (eventAnimationDriverMatchSpecCached == null) {
+        eventAnimationDriverMatchSpecCached =
+            object : EventAnimationDriverMatchSpec {
+              override fun match(viewTagRhs: Int, eventNameRhs: String): Boolean {
+                return viewTag == viewTagRhs && getEventName() == eventNameRhs
+              }
+            }
+      }
+      return eventAnimationDriverMatchSpecCached
+    }
+
+  /**
+   * Dispatch this event to JS using the given event emitter. Compatible with old and new renderer.
+   * Instead of using this or dispatchModern, it is recommended that you simply override
+   * `getEventData`.
+   */
+  @Deprecated("Prefer to override getEventData instead")
+  public open fun dispatch(rctEventEmitter: RCTEventEmitter) {
+    rctEventEmitter.receiveEvent(viewTag, getEventName(), getEventData())
+  }
+
+  /** Can be overridden by classes when no custom logic for dispatching is needed. */
+  protected open fun getEventData(): WritableMap? = null
+
+  /**
+   * NOTE: This is a transitional method that allows accessing event data from outside the
+   * sublcasses, but inside the package.
+   */
+  internal fun internal_getEventData(): WritableMap? = getEventData()
+
+  protected open fun getEventCategory(): Int = EventCategoryDef.UNSPECIFIED
+
+  /**
+   * NOTE: This is a transitional method that allows accessing event category from outside the
+   * sublcasses, but inside the package.
+   */
+  internal fun internal_getEventCategory(): Int = getEventCategory()
+
+  protected open fun experimental_isSynchronous(): Boolean = false
+
+  /**
+   * NOTE: This is a transitional method that allows accessing event category from outside the
+   * sublcasses, but inside the package.
+   */
+  internal fun internal_experimental_isSynchronous(): Boolean = experimental_isSynchronous()
+
+  /**
+   * Dispatch this event to JS using a V2 EventEmitter. If surfaceId is not -1 and `getEventData` is
+   * non-null, this will use the RCTModernEventEmitter API. Otherwise, it falls back to the
+   * old-style dispatch function. For Event classes that need to do something different, this method
+   * can always be overridden entirely, but it is not recommended.
+   *
+   * This method additionally allows C++ to coalesce events and detect continuous ones for
+   * concurrent mode (Fabric only).
+   *
+   * @see .dispatch
+   */
+  public open fun dispatchModern(rctEventEmitter: RCTModernEventEmitter) {
+    if (surfaceId != -1) {
+      rctEventEmitter.receiveEvent(
+          surfaceId,
+          viewTag,
+          getEventName(),
+          canCoalesce(),
+          getCoalescingKey().toInt(),
+          getEventData(),
+          getEventCategory())
+    } else {
+      dispatch(rctEventEmitter)
+    }
+  }
+
+  public fun interface EventAnimationDriverMatchSpec {
+    public fun match(viewTagRhs: Int, eventNameRhs: String): Boolean
+  }
+
+  private companion object {
+    private var uniqueIdCounter = 0
+  }
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/FabricEventDispatcher.kt

@@ -63,7 +63,7 @@ internal class FabricEventDispatcher(
     for (listener in listeners) {
       listener.onEventDispatch(event)
     }
-    if (event.experimental_isSynchronous()) {
+    if (event.internal_experimental_isSynchronous()) {
       dispatchSynchronous(event)
     } else {
       event.dispatchModern(eventEmitter)
@@ -76,7 +76,7 @@ internal class FabricEventDispatcher(
   private fun dispatchSynchronous(event: Event<*>) {
     Systrace.beginSection(
         Systrace.TRACE_TAG_REACT,
-        "FabricEventDispatcher.dispatchSynchronous('" + event.eventName + "')")
+        "FabricEventDispatcher.dispatchSynchronous('" + event.getEventName() + "')")
     try {
       val fabricUIManager = UIManagerHelper.getUIManager(reactContext, UIManagerType.FABRIC)
       @OptIn(UnstableReactNativeAPI::class)
@@ -84,10 +84,10 @@ internal class FabricEventDispatcher(
         (fabricUIManager as SynchronousEventReceiver).receiveEvent(
             event.surfaceId,
             event.viewTag,
-            event.eventName,
+            event.getEventName(),
             event.canCoalesce(),
-            event.eventData,
-            event.eventCategory,
+            event.internal_getEventData(),
+            event.internal_getEventCategory(),
             true)
       } else {
         ReactSoftExceptionLogger.logSoftException(

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/TouchesHelper.kt

@@ -124,7 +124,8 @@ internal object TouchesHelper {
   @JvmStatic
   public fun sendTouchEvent(eventEmitter: RCTModernEventEmitter, event: TouchEvent) {
     Systrace.beginSection(
-        Systrace.TRACE_TAG_REACT, "TouchesHelper.sentTouchEventModern(" + event.eventName + ")")
+        Systrace.TRACE_TAG_REACT,
+        "TouchesHelper.sentTouchEventModern(" + event.getEventName() + ")")
     try {
       val type = event.getTouchEventType()
       val motionEvent = event.getMotionEvent()
@@ -176,11 +177,11 @@ internal object TouchesHelper {
         eventEmitter.receiveEvent(
             event.surfaceId,
             event.viewTag,
-            event.eventName,
+            event.getEventName(),
             event.canCoalesce(),
             0,
             eventData,
-            event.eventCategory)
+            event.getEventCategory())
       }
     } finally {
       Systrace.endSection(Systrace.TRACE_TAG_REACT)

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ScrollEvent.kt

@@ -53,7 +53,9 @@ public class ScrollEvent private constructor() : Event<ScrollEvent>() {
       scrollViewWidth: Int,
       scrollViewHeight: Int,
   ) {
-    super.init(surfaceId, viewTag)
+    val timestampMs = SystemClock.uptimeMillis()
+    super.init(surfaceId, viewTag, timestampMs)
+
     this.scrollEventType = scrollEventType
     this.scrollX = scrollX
     this.scrollY = scrollY
@@ -63,7 +65,7 @@ public class ScrollEvent private constructor() : Event<ScrollEvent>() {
     this.contentHeight = contentHeight
     this.scrollViewWidth = scrollViewWidth
     this.scrollViewHeight = scrollViewHeight
-    this.timestamp = SystemClock.uptimeMillis()
+    this.timestamp = timestampMs
   }
 
   override fun getEventName(): String =

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/animated/NativeAnimatedNodeTraversalTest.kt

@@ -899,22 +899,22 @@ class NativeAnimatedNodeTraversalTest {
     verifyNoMoreInteractions(uiManagerMock)
   }
 
-  private fun createScrollEvent(tag: Int, value: Double): Event<Event<*>> {
-    return object : Event<Event<*>>(tag) {
+  private class TestScrollEvent(private val tag: Int, private val value: Double) :
+      Event<TestScrollEvent>(tag) {
 
-      override fun getEventName(): String {
-        return "topScroll"
-      }
+    override fun getEventName(): String {
+      return "topScroll"
+    }
 
-      @Override
-      @Deprecated("Deprecated in Java")
-      override fun dispatch(rctEventEmitter: RCTEventEmitter) {
-        rctEventEmitter.receiveEvent(
-            tag, "topScroll", JavaOnlyMap.of("contentOffset", JavaOnlyMap.of("y", value)))
-      }
+    @Deprecated("Deprecated in Java")
+    override fun dispatch(rctEventEmitter: RCTEventEmitter) {
+      rctEventEmitter.receiveEvent(
+          tag, "topScroll", JavaOnlyMap.of("contentOffset", JavaOnlyMap.of("y", value)))
     }
   }
 
+  private fun createScrollEvent(tag: Int, value: Double): Event<*> = TestScrollEvent(tag, value)
+
   @Test
   fun testNativeAnimatedEventDoUpdate() {
     val viewTag = 1000

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/JSPointerDispatcherTest.kt

@@ -35,8 +35,8 @@ class JSPointerDispatcherTest {
   private lateinit var root: ViewGroup
   private lateinit var pointerDispatcher: JSPointerDispatcher
 
-  class EventWithName(private val eventName: String) : ArgumentMatcher<Event<Event<*>>> {
-    override fun matches(argument: Event<Event<*>>?): Boolean = argument?.eventName == eventName
+  class EventWithName(private val eventName: String) : ArgumentMatcher<Event<*>> {
+    override fun matches(argument: Event<*>?): Boolean = argument?.getEventName() == eventName
 
     override fun toString(): String = "[event with name: $eventName]"
   }

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/OnLayoutEventTest.kt

@@ -58,7 +58,7 @@ class OnLayoutEventTest {
   fun testGetEventName_shouldReturnCorrectEventName() {
     val event = OnLayoutEvent.obtain(1, 1, 10, 20, 100, 200)
 
-    assertThat(event.eventName).isEqualTo("topLayout")
+    assertThat(event.getEventName()).isEqualTo("topLayout")
   }
 
   @Test