[WIP]add the feature that can create a new engine with FlutterEngineGroup …

ci/licenses_golden/licenses_flutter

@@ -840,6 +840,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/Flutte
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/FlutterEngineCache.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/FlutterEngineConnectionRegistry.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/FlutterEngineGroup.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/FlutterEngineGroupCache.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/FlutterJNI.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/FlutterOverlaySurface.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/FlutterShellArgs.java

shell/platform/android/BUILD.gn

@@ -187,6 +187,7 @@ android_java_sources = [
   "io/flutter/embedding/engine/FlutterEngineCache.java",
   "io/flutter/embedding/engine/FlutterEngineConnectionRegistry.java",
   "io/flutter/embedding/engine/FlutterEngineGroup.java",
+  "io/flutter/embedding/engine/FlutterEngineGroupCache.java",
   "io/flutter/embedding/engine/FlutterJNI.java",
   "io/flutter/embedding/engine/FlutterOverlaySurface.java",
   "io/flutter/embedding/engine/FlutterShellArgs.java",

shell/platform/android/io/flutter/embedding/android/FlutterActivity.java

@@ -9,7 +9,9 @@
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.DEFAULT_DART_ENTRYPOINT;
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.DEFAULT_INITIAL_ROUTE;
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.EXTRA_BACKGROUND_MODE;
+import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.EXTRA_CACHED_ENGINE_GROUP_ID;
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.EXTRA_CACHED_ENGINE_ID;
+import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.EXTRA_DART_ENTRYPOINT;
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.EXTRA_DESTROY_ENGINE_WITH_ACTIVITY;
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.EXTRA_ENABLE_STATE_RESTORATION;
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.EXTRA_INITIAL_ROUTE;
@@ -269,7 +271,7 @@ public NewEngineIntentBuilder(@NonNull Class<? extends FlutterActivity> activity
     }
 
     /**
-     * The initial route that a Flutter app will render in this {@link FlutterFragment}, defaults to
+     * The initial route that a Flutter app will render in this {@link FlutterActivity}, defaults to
      * "/".
      *
      * @param initialRoute The route.
@@ -421,6 +423,151 @@ public Intent build(@NonNull Context context) {
     }
   }
 
+  /**
+   * Creates a {@link NewEngineInGroupIntentBuilder}, which can be used to configure an {@link
+   * Intent} to launch a {@code FlutterActivity} by internally creating a FlutterEngine from an
+   * existing {@link io.flutter.embedding.engine.FlutterEngineGroup} cached in a specified {@link
+   * io.flutter.embedding.engine.FlutterEngineGroupCache}, and creates a new {@link
+   * io.flutter.embedding.engine.FlutterEngine} by FlutterEngineGroup#createAndRunEngine
+   *
+   * <pre>{@code
+   * // Create a FlutterEngineGroup, usually we could create it in onCreate method of Application.
+   * FlutterEngineGroup engineGroup = new FlutterEngineGroup(this);
+   * FlutterEngineGroupCache.getInstance().put("my_cached_engine_group_id", engineGroup);
+   *
+   * // use the intent that build by withNewEngineInGroup to start FlutterActivity
+   * Intent intent = FlutterActivity.withNewEngineInGroup("my_cached_engine_group_id")
+   *     .dartEntrypoint("custom_entrypoint")
+   *     .initialRoute("/custom/route")
+   *     .backgroundMode(BackgroundMode.transparent)
+   *     .build(context);
+   * startActivity(intent);
+   * }</pre>
+   *
+   * @param engineGroupId A cached engine group ID.
+   * @return The builder.
+   */
+  public static NewEngineInGroupIntentBuilder withNewEngineInGroup(@NonNull String engineGroupId) {
+    return new NewEngineInGroupIntentBuilder(FlutterActivity.class, engineGroupId);
+  }
+
+  /**
+   * Builder to create an {@code Intent} that launches a {@code FlutterActivity} with a new {@link
+   * FlutterEngine} by FlutterEngineGroup#createAndRunEngine.
+   */
+  public static class NewEngineInGroupIntentBuilder {
+    private final Class<? extends FlutterActivity> activityClass;
+    private final String cachedEngineGroupId;
+    private String dartEntrypoint = DEFAULT_DART_ENTRYPOINT;
+    private String initialRoute = DEFAULT_INITIAL_ROUTE;
+    private String backgroundMode = DEFAULT_BACKGROUND_MODE;
+
+    /**
+     * Constructor that allows this {@code NewEngineInGroupIntentBuilder} to be used by subclasses
+     * of {@code FlutterActivity}.
+     *
+     * <p>Subclasses of {@code FlutterActivity} should provide their own static version of {@link
+     * #withNewEngineInGroup}, which returns an instance of {@code NewEngineInGroupIntentBuilder}
+     * constructed with a {@code Class} reference to the {@code FlutterActivity} subclass, e.g.:
+     *
+     * <p>{@code return new NewEngineInGroupIntentBuilder(MyFlutterActivity.class,
+     * cacheedEngineGroupId); }
+     *
+     * <pre>{@code
+     * // Create a FlutterEngineGroup, usually we could create it in onCreate method of Application.
+     * FlutterEngineGroup engineGroup = new FlutterEngineGroup(this);
+     * FlutterEngineGroupCache.getInstance().put("my_cached_engine_group_id", engineGroup);
+     *
+     * // create NewEngineInGroupIntentBuilder, and start my custom FlutterActivity with the intent
+     * // that build by NewEngineInGroupIntentBuilder.
+     * FlutterActivity.NewEngineInGroupIntentBuilder intentBuilder =
+     *     new FlutterActivity.NewEngineInGroupIntentBuilder(
+     *           MyFlutterActivity.class,
+     *           app.engineGroupId);
+     * intentBuilder.dartEntrypoint("main")
+     *     .initialRoute("/custom/route")
+     *     .backgroundMode(BackgroundMode.transparent);
+     * startActivity(intentBuilder.build(context));
+     * }</pre>
+     *
+     * @param activityClass A subclass of {@code FlutterActivity}.
+     * @param engineGroupId The engine group id.
+     */
+    public NewEngineInGroupIntentBuilder(
+        @NonNull Class<? extends FlutterActivity> activityClass, @NonNull String engineGroupId) {
+      this.activityClass = activityClass;
+      this.cachedEngineGroupId = engineGroupId;
+    }
+
+    /**
+     * The Dart entrypoint that will be executed in the newly created FlutterEngine as soon as the
+     * Dart snapshot is loaded. Default to "main".
+     *
+     * @param dartEntrypoint The dart entrypoint's name
+     * @return The engine group intent builder
+     */
+    @NonNull
+    public NewEngineInGroupIntentBuilder dartEntrypoint(@NonNull String dartEntrypoint) {
+      this.dartEntrypoint = dartEntrypoint;
+      return this;
+    }
+
+    /**
+     * The initial route that a Flutter app will render in this {@link FlutterActivity}, defaults to
+     * "/".
+     *
+     * @param initialRoute The route.
+     * @return The engine group intent builder.
+     */
+    @NonNull
+    public NewEngineInGroupIntentBuilder initialRoute(@NonNull String initialRoute) {
+      this.initialRoute = initialRoute;
+      return this;
+    }
+
+    /**
+     * The mode of {@code FlutterActivity}'s background, either {@link BackgroundMode#opaque} or
+     * {@link BackgroundMode#transparent}.
+     *
+     * <p>The default background mode is {@link BackgroundMode#opaque}.
+     *
+     * <p>Choosing a background mode of {@link BackgroundMode#transparent} will configure the inner
+     * {@link FlutterView} of this {@code FlutterActivity} to be configured with a {@link
+     * FlutterTextureView} to support transparency. This choice has a non-trivial performance
+     * impact. A transparent background should only be used if it is necessary for the app design
+     * being implemented.
+     *
+     * <p>A {@code FlutterActivity} that is configured with a background mode of {@link
+     * BackgroundMode#transparent} must have a theme applied to it that includes the following
+     * property: {@code <item name="android:windowIsTranslucent">true</item>}.
+     *
+     * @param backgroundMode The background mode.
+     * @return The engine group intent builder.
+     */
+    @NonNull
+    public NewEngineInGroupIntentBuilder backgroundMode(@NonNull BackgroundMode backgroundMode) {
+      this.backgroundMode = backgroundMode.name();
+      return this;
+    }
+
+    /**
+     * Creates and returns an {@link Intent} that will launch a {@code FlutterActivity} with the
+     * desired configuration.
+     *
+     * @param context The context. e.g. An Activity.
+     * @return The intent.
+     */
+    @NonNull
+    public Intent build(@NonNull Context context) {
+      return new Intent(context, activityClass)
+          .putExtra(EXTRA_DART_ENTRYPOINT, dartEntrypoint)
+          .putExtra(EXTRA_INITIAL_ROUTE, initialRoute)
+          .putExtra(EXTRA_CACHED_ENGINE_GROUP_ID, cachedEngineGroupId)
+          .putExtra(EXTRA_BACKGROUND_MODE, backgroundMode)
+          .putExtra(EXTRA_DESTROY_ENGINE_WITH_ACTIVITY, true);
+    }
+  }
+
   // Delegate that runs all lifecycle and OS hook logic that is common between
   // FlutterActivity and FlutterFragment. See the FlutterActivityAndFragmentDelegate
   // implementation for details about why it exists.
@@ -775,6 +922,17 @@ public String getCachedEngineId() {
     return getIntent().getStringExtra(EXTRA_CACHED_ENGINE_ID);
   }
 
+  /**
+   * Returns the ID of a statically cached {@link io.flutter.embedding.engine.FlutterEngineGroup} to
+   * use within this {@code FlutterActivity}, or {@code null} if this {@code FlutterActivity} does
+   * not want to use a cached {@link io.flutter.embedding.engine.FlutterEngineGroup}.
+   */
+  @Override
+  @Nullable
+  public String getCachedEngineGroupId() {
+    return getIntent().getStringExtra(EXTRA_CACHED_ENGINE_GROUP_ID);
+  }
+
   /**
    * Returns false if the {@link io.flutter.embedding.engine.FlutterEngine} backing this {@code
    * FlutterActivity} should outlive this {@code FlutterActivity}, or true to be destroyed when the
@@ -801,14 +959,26 @@ public boolean shouldDestroyEngineWithHost() {
   /**
    * The Dart entrypoint that will be executed as soon as the Dart snapshot is loaded.
    *
-   * <p>This preference can be controlled by setting a {@code <meta-data>} called {@link
-   * FlutterActivityLaunchConfigs#DART_ENTRYPOINT_META_DATA_KEY} within the Android manifest
-   * definition for this {@code FlutterActivity}.
+   * <p>This preference can be controlled with 2 methods:
+   *
+   * <ol>
+   *   <li>Pass a boolean as {@link FlutterActivityLaunchConfigs#EXTRA_DART_ENTRYPOINT} with the
+   *       launching {@code Intent}, or
+   *   <li>Set a {@code <meta-data>} called {@link
+   *       FlutterActivityLaunchConfigs#DART_ENTRYPOINT_META_DATA_KEY} within the Android manifest
+   *       definition for this {@code FlutterActivity}
+   * </ol>
+   *
+   * If both preferences are set, the {@code Intent} preference takes priority.
    *
    * <p>Subclasses may override this method to directly control the Dart entrypoint.
    */
   @NonNull
   public String getDartEntrypointFunctionName() {
+    if (getIntent().hasExtra(EXTRA_DART_ENTRYPOINT)) {
+      return getIntent().getStringExtra(EXTRA_DART_ENTRYPOINT);
+    }
+
     try {
       Bundle metaData = getMetaData();
       String desiredDartEntrypoint =

shell/platform/android/io/flutter/embedding/android/FlutterActivityAndFragmentDelegate.java

@@ -24,6 +24,8 @@
 import io.flutter.Log;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterEngineCache;
+import io.flutter.embedding.engine.FlutterEngineGroup;
+import io.flutter.embedding.engine.FlutterEngineGroupCache;
 import io.flutter.embedding.engine.FlutterShellArgs;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import io.flutter.embedding.engine.renderer.FlutterUiDisplayListener;
@@ -213,6 +215,10 @@ void onAttach(@NonNull Context context) {
    * <p>Second, the {@code host} is given an opportunity to provide a {@link
    * io.flutter.embedding.engine.FlutterEngine} via {@link Host#provideFlutterEngine(Context)}.
    *
+   * <p>Third, the {@code host} is given an FluttenEngineGroup Id, then used a cached {@link
+   * io.flutter.embedding.engine.FlutterEngineGroup} to create a new {@link FlutterEngine} by {@link
+   * FlutterEngineGroup#createAndRunEngine}
+   *
    * <p>If the {@code host} does not provide a {@link io.flutter.embedding.engine.FlutterEngine},
    * then a new {@link FlutterEngine} is instantiated.
    */
@@ -241,6 +247,34 @@ void onAttach(@NonNull Context context) {
       return;
     }
 
+    // Third, check if the host wants to use a cached FlutterEngineGroup
+    // and create new FlutterEngine by FlutterEngineGroup#createAndRunEngine
+    String cachedEngineGroupId = host.getCachedEngineGroupId();
+    if (cachedEngineGroupId != null) {
+      FlutterEngineGroup flutterEngineGroup =
+          FlutterEngineGroupCache.getInstance().get(cachedEngineGroupId);
+      if (flutterEngineGroup == null) {
+        throw new IllegalStateException(
+            "The requested cached FlutterEngineGroup did not exist in the FlutterEngineGroupCache: '"
+                + cachedEngineGroupId
+                + "'");
+      }
+
+      String appBundlePathOverride = host.getAppBundlePath();
+      if (appBundlePathOverride == null || appBundlePathOverride.isEmpty()) {
+        appBundlePathOverride = FlutterInjector.instance().flutterLoader().findAppBundlePath();
+      }
+
+      DartExecutor.DartEntrypoint dartEntrypoint =
+          new DartExecutor.DartEntrypoint(
+              appBundlePathOverride, host.getDartEntrypointFunctionName());
+      flutterEngine =
+          flutterEngineGroup.createAndRunEngine(
+              host.getContext(), dartEntrypoint, host.getInitialRoute());
+      isFlutterEngineFromHost = false;
+      return;
+    }
+
     // Our host did not provide a custom FlutterEngine. Create a FlutterEngine to back our
     // FlutterView.
     Log.v(
@@ -876,6 +910,9 @@ private void ensureAlive() {
     @Nullable
     String getCachedEngineId();
 
+    @Nullable
+    String getCachedEngineGroupId();
+
     /**
      * Returns true if the {@link io.flutter.embedding.engine.FlutterEngine} used in this delegate
      * should be destroyed when the host/delegate are destroyed.

shell/platform/android/io/flutter/embedding/android/FlutterActivityLaunchConfigs.java

@@ -19,9 +19,11 @@ public class FlutterActivityLaunchConfigs {
   /* package */ static final String HANDLE_DEEPLINKING_META_DATA_KEY =
       "flutter_deeplinking_enabled";
   // Intent extra arguments.
+  /* package */ static final String EXTRA_DART_ENTRYPOINT = "dart_entrypoint";
   /* package */ static final String EXTRA_INITIAL_ROUTE = "route";
   /* package */ static final String EXTRA_BACKGROUND_MODE = "background_mode";
   /* package */ static final String EXTRA_CACHED_ENGINE_ID = "cached_engine_id";
+  /* package */ static final String EXTRA_CACHED_ENGINE_GROUP_ID = "cached_engine_group_id";
   /* package */ static final String EXTRA_DESTROY_ENGINE_WITH_ACTIVITY =
       "destroy_engine_with_activity";
   /* package */ static final String EXTRA_ENABLE_STATE_RESTORATION = "enable_state_restoration";