Event should infer UIManagerType by presence of SurfaceId

Summary:
See comments inline for motivation. It's not safe to use viewtag of an Event to infer whether or not the view is in a Fabric or non-Fabric RootView.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D28365566

fbshipit-source-id: 187ddcc5d5a43a31a71232fdb2f1f5b334bec8c2

Author: JoshuaGross

ReactAndroid/src/main/java/com/facebook/react/animated/NativeAnimatedNodesManager.java

@@ -535,7 +535,7 @@ private void handleEvent(Event event) {
         return;
       }
       UIManager uiManager =
-          UIManagerHelper.getUIManagerForReactTag(mReactApplicationContext, event.getViewTag());
+          UIManagerHelper.getUIManager(mReactApplicationContext, event.getUIManagerType());
       if (uiManager == null) {
         return;
       }

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

@@ -11,6 +11,7 @@
 import com.facebook.react.bridge.WritableMap;
 import com.facebook.react.common.SystemClock;
 import com.facebook.react.uimanager.IllegalViewOperationException;
+import com.facebook.react.uimanager.common.UIManagerType;
 
 /**
  * A UI event that can be dispatched to JS.
@@ -33,6 +34,7 @@ public abstract class Event<T extends Event> {
   private static int sUniqueID = 0;
 
   private boolean mInitialized;
+  private @UIManagerType int mUIManagerType;
   private int mSurfaceId;
   private int mViewTag;
   private long mTimestampMs;
@@ -67,10 +69,23 @@ protected void init(int viewTag) {
   protected void init(int surfaceId, int viewTag) {
     mSurfaceId = surfaceId;
     mViewTag = viewTag;
-    mInitialized = true;
+
+    // We infer UIManagerType. Even though it's not passed in explicitly, we have a
+    // contract that Fabric events *always* have a SurfaceId passed in, and non-Fabric events
+    // NEVER have a SurfaceId passed in (the default/placeholder of -1 is passed in instead).
+    // Why does this matter?
+    // Events can be sent to Views that are part of the View hierarchy *but not directly managed
+    // by React Native*. For example, embedded custom hierachies, Litho hierachies, etc.
+    // In those cases it's important to konw that the Event should be sent to the Fabric or
+    // non-Fabric UIManager, and we cannot use the ViewTag for inference since it's not controlled
+    // by RN and is essentially a random number.
+    // At some point it would be great to pass the SurfaceContext here instead.
+    mUIManagerType = (surfaceId == -1 ? UIManagerType.DEFAULT : UIManagerType.FABRIC);
 
     // This is a *relative* time. See `getUnixTimestampMs`.
     mTimestampMs = SystemClock.uptimeMillis();
+
+    mInitialized = true;
   }
 
   /** @return the view id for the view that generated this event */
@@ -142,6 +157,10 @@ public void onDispose() {}
     onDispose();
   }
 
+  public final @UIManagerType int getUIManagerType() {
+    return mUIManagerType;
+  }
+
   /** @return the name of this event as registered in JS */
   public abstract String getEventName();