[google_maps_flutter] Clean up google_maps_flutter plugin (flutter#3206)

1. A few minor formatting changes and additions of @nullable annotations
2. Removed pass-through of activityHashCode. In the legacy plugin use case, the value is always -1 (which has been inlined). In the new plugin use case, the value should never be used because it uses DefaultLifecycleCallbacks instead of ActivityLifecycleCallbacks.
3. Replaced custom lifecycle state ints with androidx.lifecycle.Lifecycle.State enum. Also simplify paused/stopped states, which don't need their own dedicated states. Paused == started and stopped == created.
4. Fixed a bug where the Lifecycle object was being leaked onDetachFromActivity by nulling out the field.
5. Moved GoogleMapListener to its own file. Declaring multiple top level classes in the same file is bad practice.

Author: math1man

packages/google_maps_flutter/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/GoogleMapBuilder.java

@@ -4,12 +4,17 @@
 
 package io.flutter.plugins.googlemaps;
 
+import android.app.Application;
 import android.content.Context;
 import android.graphics.Rect;
+import androidx.annotation.Nullable;
+import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.Lifecycle.State;
 import com.google.android.gms.maps.GoogleMapOptions;
 import com.google.android.gms.maps.model.CameraPosition;
 import com.google.android.gms.maps.model.LatLngBounds;
 import io.flutter.plugin.common.BinaryMessenger;
+import io.flutter.plugin.common.PluginRegistry;
 
 class GoogleMapBuilder implements GoogleMapOptionsSink {
   private final GoogleMapOptions options = new GoogleMapOptions();
@@ -28,11 +33,15 @@ class GoogleMapBuilder implements GoogleMapOptionsSink {
   GoogleMapController build(
       int id,
       Context context,
+      State lifecycleState,
       BinaryMessenger binaryMessenger,
-      LifecycleProvider lifecycleProvider) {
+      @Nullable Application application,
+      @Nullable Lifecycle lifecycle,
+      @Nullable PluginRegistry.Registrar registrar) {
     final GoogleMapController controller =
-        new GoogleMapController(id, context, binaryMessenger, lifecycleProvider, options);
-    controller.init();
+        new GoogleMapController(
+            id, context, binaryMessenger, application, lifecycle, registrar, options);
+    controller.init(lifecycleState);
     controller.setMyLocationEnabled(myLocationEnabled);
     controller.setMyLocationButtonEnabled(myLocationButtonEnabled);
     controller.setIndoorEnabled(indoorEnabled);

packages/google_maps_flutter/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/GoogleMapController.java

@@ -6,6 +6,8 @@
 
 import android.Manifest;
 import android.annotation.SuppressLint;
+import android.app.Activity;
+import android.app.Application;
 import android.content.Context;
 import android.content.pm.PackageManager;
 import android.graphics.Bitmap;
@@ -17,6 +19,7 @@
 import androidx.annotation.Nullable;
 import androidx.lifecycle.DefaultLifecycleObserver;
 import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.Lifecycle.State;
 import androidx.lifecycle.LifecycleOwner;
 import com.google.android.gms.maps.CameraUpdate;
 import com.google.android.gms.maps.GoogleMap;
@@ -36,6 +39,7 @@
 import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
+import io.flutter.plugin.common.PluginRegistry;
 import io.flutter.plugin.platform.PlatformView;
 import java.io.ByteArrayOutputStream;
 import java.util.ArrayList;
@@ -46,7 +50,8 @@
 
 /** Controller of a single GoogleMaps MapView instance. */
 final class GoogleMapController
-    implements DefaultLifecycleObserver,
+    implements Application.ActivityLifecycleCallbacks,
+        DefaultLifecycleObserver,
         ActivityPluginBinding.OnSaveInstanceStateListener,
         GoogleMapOptionsSink,
         MethodChannel.MethodCallHandler,
@@ -70,8 +75,12 @@ final class GoogleMapController
   private boolean disposed = false;
   private final float density;
   private MethodChannel.Result mapReadyResult;
+  @Nullable private final Lifecycle lifecycle;
   private final Context context;
-  private final LifecycleProvider lifecycleProvider;
+  // Do not use directly, use getApplication() instead to get correct application object for both v1
+  // and v2 embedding.
+  @Nullable private final Application mApplication;
+  @Nullable private final PluginRegistry.Registrar registrar; // For v1 embedding only.
   private final MarkersController markersController;
   private final PolygonsController polygonsController;
   private final PolylinesController polylinesController;
@@ -85,7 +94,9 @@ final class GoogleMapController
       int id,
       Context context,
       BinaryMessenger binaryMessenger,
-      LifecycleProvider lifecycleProvider,
+      @Nullable Application application,
+      @Nullable Lifecycle lifecycle,
+      @Nullable PluginRegistry.Registrar registrar,
       GoogleMapOptions options) {
     this.id = id;
     this.context = context;
@@ -94,7 +105,9 @@ final class GoogleMapController
     this.density = context.getResources().getDisplayMetrics().density;
     methodChannel = new MethodChannel(binaryMessenger, "plugins.flutter.io/google_maps_" + id);
     methodChannel.setMethodCallHandler(this);
-    this.lifecycleProvider = lifecycleProvider;
+    mApplication = application;
+    this.lifecycle = lifecycle;
+    this.registrar = registrar;
     this.markersController = new MarkersController(methodChannel);
     this.polygonsController = new PolygonsController(methodChannel, density);
     this.polylinesController = new PolylinesController(methodChannel, density);
@@ -106,8 +119,30 @@ public View getView() {
     return mapView;
   }
 
-  void init() {
-    lifecycleProvider.getLifecycle().addObserver(this);
+  void init(State lifecycleState) {
+    switch (lifecycleState) {
+      case RESUMED:
+        mapView.onCreate(null);
+        mapView.onStart();
+        mapView.onResume();
+        break;
+      case STARTED:
+        mapView.onCreate(null);
+        mapView.onStart();
+        break;
+      case CREATED:
+        mapView.onCreate(null);
+        break;
+      case DESTROYED:
+      case INITIALIZED:
+        // Nothing to do, the activity has been completely destroyed or not yet created.
+        break;
+    }
+    if (lifecycle != null) {
+      lifecycle.addObserver(this);
+    } else {
+      getApplication().registerActivityLifecycleCallbacks(this);
+    }
     mapView.getMapAsync(this);
   }
 
@@ -472,10 +507,7 @@ public void dispose() {
     methodChannel.setMethodCallHandler(null);
     setGoogleMapListener(null);
     destroyMapViewIfNecessary();
-    Lifecycle lifecycle = lifecycleProvider.getLifecycle();
-    if (lifecycle != null) {
-      lifecycle.removeObserver(this);
-    }
+    getApplication().unregisterActivityLifecycleCallbacks(this);
   }
 
   private void setGoogleMapListener(@Nullable GoogleMapListener listener) {
@@ -505,7 +537,64 @@ public void onInputConnectionUnlocked() {
     // TODO(mklim): Remove this empty override once https://github.com/flutter/flutter/issues/40126 is fixed in stable.
   }
 
-  // DefaultLifecycleObserver
+  // Application.ActivityLifecycleCallbacks methods
+  @Override
+  public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
+    if (disposed || activity.hashCode() != getActivityHashCode()) {
+      return;
+    }
+    mapView.onCreate(savedInstanceState);
+  }
+
+  @Override
+  public void onActivityStarted(Activity activity) {
+    if (disposed || activity.hashCode() != getActivityHashCode()) {
+      return;
+    }
+    mapView.onStart();
+  }
+
+  @Override
+  public void onActivityResumed(Activity activity) {
+    if (disposed || activity.hashCode() != getActivityHashCode()) {
+      return;
+    }
+    mapView.onResume();
+  }
+
+  @Override
+  public void onActivityPaused(Activity activity) {
+    if (disposed || activity.hashCode() != getActivityHashCode()) {
+      return;
+    }
+    mapView.onPause();
+  }
+
+  @Override
+  public void onActivityStopped(Activity activity) {
+    if (disposed || activity.hashCode() != getActivityHashCode()) {
+      return;
+    }
+    mapView.onStop();
+  }
+
+  @Override
+  public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
+    if (disposed || activity.hashCode() != getActivityHashCode()) {
+      return;
+    }
+    mapView.onSaveInstanceState(outState);
+  }
+
+  @Override
+  public void onActivityDestroyed(Activity activity) {
+    if (disposed || activity.hashCode() != getActivityHashCode()) {
+      return;
+    }
+    destroyMapViewIfNecessary();
+  }
+
+  // DefaultLifecycleObserver and OnSaveInstanceStateListener
 
   @Override
   public void onCreate(@NonNull LifecycleOwner owner) {
@@ -549,7 +638,6 @@ public void onStop(@NonNull LifecycleOwner owner) {
 
   @Override
   public void onDestroy(@NonNull LifecycleOwner owner) {
-    owner.getLifecycle().removeObserver(this);
     if (disposed) {
       return;
     }
@@ -760,6 +848,24 @@ private int checkSelfPermission(String permission) {
         permission, android.os.Process.myPid(), android.os.Process.myUid());
   }
 
+  private int getActivityHashCode() {
+    if (registrar != null && registrar.activity() != null) {
+      return registrar.activity().hashCode();
+    } else {
+      // TODO(cyanglaz): Remove `getActivityHashCode()` and use a cached hashCode when creating the view for V1 embedding.
+      // https://github.com/flutter/flutter/issues/69128
+      return -1;
+    }
+  }
+
+  private Application getApplication() {
+    if (registrar != null && registrar.activity() != null) {
+      return registrar.activity().getApplication();
+    } else {
+      return mApplication;
+    }
+  }
+
   private void destroyMapViewIfNecessary() {
     if (mapView == null) {
       return;

packages/google_maps_flutter/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/GoogleMapFactory.java

@@ -4,23 +4,40 @@
 
 package io.flutter.plugins.googlemaps;
 
+import android.app.Application;
 import android.content.Context;
+import androidx.annotation.Nullable;
+import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.Lifecycle.State;
 import com.google.android.gms.maps.model.CameraPosition;
 import io.flutter.plugin.common.BinaryMessenger;
+import io.flutter.plugin.common.PluginRegistry;
 import io.flutter.plugin.common.StandardMessageCodec;
 import io.flutter.plugin.platform.PlatformView;
 import io.flutter.plugin.platform.PlatformViewFactory;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
 
 public class GoogleMapFactory extends PlatformViewFactory {
 
+  private final AtomicReference<State> lifecycleState;
   private final BinaryMessenger binaryMessenger;
-  private final LifecycleProvider lifecycleProvider;
+  @Nullable private final Application application;
+  @Nullable private final Lifecycle lifecycle;
+  @Nullable private final PluginRegistry.Registrar registrar; // V1 embedding only.
 
-  GoogleMapFactory(BinaryMessenger binaryMessenger, LifecycleProvider lifecycleProvider) {
+  GoogleMapFactory(
+      AtomicReference<State> lifecycleState,
+      BinaryMessenger binaryMessenger,
+      @Nullable Application application,
+      @Nullable Lifecycle lifecycle,
+      @Nullable PluginRegistry.Registrar registrar) {
     super(StandardMessageCodec.INSTANCE);
+    this.lifecycleState = lifecycleState;
     this.binaryMessenger = binaryMessenger;
-    this.lifecycleProvider = lifecycleProvider;
+    this.application = application;
+    this.lifecycle = lifecycle;
+    this.registrar = registrar;
   }
 
   @SuppressWarnings("unchecked")
@@ -46,6 +63,7 @@ public PlatformView create(Context context, int id, Object args) {
     if (params.containsKey("circlesToAdd")) {
       builder.setInitialCircles(params.get("circlesToAdd"));
     }
-    return builder.build(id, context, binaryMessenger, lifecycleProvider);
+    return builder.build(
+        id, context, lifecycleState.get(), binaryMessenger, application, lifecycle, registrar);
   }
 }