Expose an API to enable Concurrent Root on Android

ReactAndroid/src/main/java/com/facebook/react/ReactActivityDelegate.java

@@ -15,6 +15,7 @@
 import android.os.Build;
 import android.os.Bundle;
 import android.view.KeyEvent;
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import com.facebook.infer.annotation.Assertions;
 import com.facebook.react.bridge.Callback;
@@ -33,6 +34,7 @@ public class ReactActivityDelegate {
   private @Nullable PermissionListener mPermissionListener;
   private @Nullable Callback mPermissionsCallback;
   private ReactDelegate mReactDelegate;
+  private boolean mConcurrentRootEnabled;
 
   @Deprecated
   public ReactActivityDelegate(Activity activity, @Nullable String mainComponentName) {
@@ -45,10 +47,27 @@ public ReactActivityDelegate(ReactActivity activity, @Nullable String mainCompon
     mMainComponentName = mainComponentName;
   }
 
+  /**
+   * Public API to populate the launch options that will be passed to React. Here you can customize
+   * the values that will be passed as `initialProperties` to the Renderer.
+   *
+   * @return Either null or a key-value map as a Bundle
+   */
   protected @Nullable Bundle getLaunchOptions() {
     return null;
   }
 
+  private @NonNull Bundle composeLaunchOptions() {
+    Bundle composedLaunchOptions = getLaunchOptions();
+    if (isConcurrentRootEnabled()) {
+      if (composedLaunchOptions == null) {
+        composedLaunchOptions = new Bundle();
+      }
+      composedLaunchOptions.putBoolean("concurrentRoot", true);
+    }
+    return composedLaunchOptions;
+  }
+
   protected ReactRootView createRootView() {
     return new ReactRootView(getContext());
   }
@@ -74,9 +93,10 @@ public String getMainComponentName() {
 
   protected void onCreate(Bundle savedInstanceState) {
     String mainComponentName = getMainComponentName();
+    Bundle launchOptions = composeLaunchOptions();
     mReactDelegate =
         new ReactDelegate(
-            getPlainActivity(), getReactNativeHost(), mainComponentName, getLaunchOptions()) {
+            getPlainActivity(), getReactNativeHost(), mainComponentName, launchOptions) {
           @Override
           protected ReactRootView createRootView() {
             return ReactActivityDelegate.this.createRootView();
@@ -190,4 +210,16 @@ protected Context getContext() {
   protected Activity getPlainActivity() {
     return ((Activity) getContext());
   }
+
+  /**
+   * Override this method to enable Concurrent Root on the surface for this Activity. See:
+   * https://reactjs.org/blog/2022/03/29/react-v18.html
+   *
+   * <p>This requires to be rendering on Fabric (i.e. on the New Architecture).
+   *
+   * @return Wether you want to enable Concurrent Root for this surface or not.
+   */
+  protected boolean isConcurrentRootEnabled() {
+    return false;
+  }
 }

ReactAndroid/src/test/java/com/facebook/react/ReactActivityDelegateTest.kt

@@ -0,0 +1,62 @@
+/*
+ * 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
+
+import android.os.Bundle
+import org.junit.Assert.*
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+
+@RunWith(RobolectricTestRunner::class)
+class ReactActivityDelegateTest {
+
+  @Test
+  fun delegateWithConcurrentRoot_populatesInitialPropsCorrectly() {
+    val delegate =
+        object : ReactActivityDelegate(null, "test-delegate") {
+          override fun isConcurrentRootEnabled() = true
+          public val inspectLaunchOptions: Bundle?
+            get() = getLaunchOptions()
+        }
+
+    assertNotNull(delegate.inspectLaunchOptions)
+    assertTrue(delegate.inspectLaunchOptions!!.containsKey("concurrentRoot"))
+    assertTrue(delegate.inspectLaunchOptions!!.getBoolean("concurrentRoot"))
+  }
+
+  @Test
+  fun delegateWithoutConcurrentRoot_hasNullInitialProperties() {
+    val delegate =
+        object : ReactActivityDelegate(null, "test-delegate") {
+          override fun isConcurrentRootEnabled() = false
+          public val inspectLaunchOptions: Bundle?
+            get() = getLaunchOptions()
+        }
+
+    assertNull(delegate.inspectLaunchOptions)
+  }
+
+  @Test
+  fun delegateWithConcurrentRoot_composesInitialPropertiesCorrectly() {
+    val delegate =
+        object : ReactActivityDelegate(null, "test-delegate") {
+          override fun isConcurrentRootEnabled() = true
+          override fun getLaunchOptions(): Bundle =
+              Bundle().apply { putString("test-property", "test-value") }
+          public val inspectLaunchOptions: Bundle?
+            get() = getLaunchOptions()
+        }
+
+    assertNotNull(delegate.inspectLaunchOptions)
+    assertTrue(delegate.inspectLaunchOptions!!.containsKey("concurrentRoot"))
+    assertTrue(delegate.inspectLaunchOptions!!.getBoolean("concurrentRoot"))
+    assertTrue(delegate.inspectLaunchOptions!!.containsKey("test-property"))
+    assertEquals("test-value", delegate.inspectLaunchOptions!!.getString("test-property"))
+  }
+}

packages/rn-tester/android/app/src/main/java/com/facebook/react/uiapp/RNTesterActivity.java

@@ -51,6 +51,11 @@ protected void onCreate(Bundle savedInstanceState) {
     protected Bundle getLaunchOptions() {
       return mInitialProps;
     }
+
+    @Override
+    protected boolean isConcurrentRootEnabled() {
+      return true;
+    }
   }
 
   @Override

template/android/app/src/main/java/com/helloworld/MainActivity.java

@@ -37,5 +37,12 @@ protected ReactRootView createRootView() {
       reactRootView.setIsFabric(BuildConfig.IS_NEW_ARCHITECTURE_ENABLED);
       return reactRootView;
     }
+
+    @Override
+    protected boolean isConcurrentRootEnabled() {
+      // If you opted-in for the New Architecture, we enable Concurrent Root (i.e. React 18).
+      // More on this on https://reactjs.org/blog/2022/03/29/react-v18.html
+      return BuildConfig.IS_NEW_ARCHITECTURE_ENABLED;
+    }
   }
 }