Modify according to review comments.

Author: 0xZOne

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

@@ -4,7 +4,6 @@
 
 package io.flutter.embedding.android;
 
-import static android.content.ComponentCallbacks2.TRIM_MEMORY_COMPLETE;
 import static android.content.ComponentCallbacks2.TRIM_MEMORY_RUNNING_LOW;
 import static io.flutter.embedding.android.FlutterActivityLaunchConfigs.DEFAULT_INITIAL_ROUTE;
 
@@ -849,22 +848,6 @@ void onTrimMemory(int level) {
     }
   }
 
-  /**
-   * Invoke this from {@link android.app.Activity#onLowMemory()}.
-   *
-   * <p>A {@code Fragment} host must have its containing {@code Activity} forward this call so that
-   * the {@code Fragment} can then invoke this method.
-   *
-   * <p>This method sends a "memory pressure warning" message to Flutter over the "system channel".
-   */
-  void onLowMemory() {
-    Log.v(TAG, "Forwarding onLowMemory() to FlutterEngine.");
-    ensureAlive();
-    flutterEngine.getDartExecutor().notifyLowMemoryWarning();
-    flutterEngine.getSystemChannel().sendMemoryPressureWarning();
-    flutterEngine.getRenderer().onTrimMemory(TRIM_MEMORY_COMPLETE);
-  }
-
   /**
    * Ensures that this delegate has not been {@link #release()}'ed.
    *

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

@@ -980,19 +980,6 @@ public void onTrimMemory(int level) {
     }
   }
 
-  /**
-   * Callback invoked when memory is low.
-   *
-   * <p>This implementation forwards a memory pressure warning to the running Flutter app.
-   */
-  @Override
-  public void onLowMemory() {
-    super.onLowMemory();
-    if (stillAttachedForEvent("onLowMemory")) {
-      delegate.onLowMemory();
-    }
-  }
-
   /**
    * {@link FlutterActivityAndFragmentDelegate.Host} method that is used by {@link
    * FlutterActivityAndFragmentDelegate} to obtain Flutter shell arguments when initializing

shell/platform/android/io/flutter/embedding/engine/renderer/FlutterRenderer.java

@@ -13,14 +13,17 @@
 import android.view.Surface;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
 import io.flutter.Log;
 import io.flutter.embedding.engine.FlutterJNI;
 import io.flutter.view.TextureRegistry;
+import java.lang.ref.WeakReference;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
-import java.util.concurrent.CopyOnWriteArraySet;
 import java.util.concurrent.atomic.AtomicLong;
 
 /**
@@ -47,8 +50,8 @@ public class FlutterRenderer implements TextureRegistry {
   private Handler handler = new Handler();
 
   @NonNull
-  private final Set<TextureRegistry.OnLowMemoryListener> onLowMemoryListeners =
-      new CopyOnWriteArraySet<>();
+  private final Set<WeakReference<TextureRegistry.OnTrimMemoryListener>> onTrimMemoryListeners =
+      new HashSet<>();
 
   @NonNull
   private final FlutterUiDisplayListener flutterUiDisplayListener =
@@ -98,16 +101,25 @@ public void removeIsDisplayingFlutterUiListener(@NonNull FlutterUiDisplayListene
   }
 
   /** Adds a listener that is invoked when a memory pressure warning was forward. */
-  public void addOnLowMemoryListener(@NonNull OnLowMemoryListener listener) {
-    onLowMemoryListeners.add(listener);
+  @VisibleForTesting
+  /* package */ void addOnTrimMemoryListener(@NonNull OnTrimMemoryListener listener) {
+    onTrimMemoryListeners.add(new WeakReference<>(listener));
   }
 
   /**
-   * Removes a {@link OnLowMemoryListener} that was added with {@link
-   * #addOnLowMemoryListener(OnLowMemoryListener)}.
+   * Removes a {@link OnTrimMemoryListener} that was added with {@link
+   * #addOnTrimMemoryListener(OnTrimMemoryListener)}.
    */
-  public void removeOnLowMemoryListener(@NonNull OnLowMemoryListener listener) {
-    onLowMemoryListeners.remove(listener);
+  @VisibleForTesting
+  /* package */ void removeOnTrimMemoryListener(@NonNull OnTrimMemoryListener listener) {
+    final Iterator<WeakReference<OnTrimMemoryListener>> iterator = onTrimMemoryListeners.iterator();
+    while (iterator.hasNext()) {
+      final WeakReference<OnTrimMemoryListener> listenerRef = iterator.next();
+      if (listenerRef.get() == listener) {
+        iterator.remove();
+        break;
+      }
+    }
   }
 
   // ------ START TextureRegistry IMPLEMENTATION -----
@@ -133,23 +145,34 @@ public SurfaceTextureEntry registerSurfaceTexture(@NonNull SurfaceTexture surfac
         new SurfaceTextureRegistryEntry(nextTextureId.getAndIncrement(), surfaceTexture);
     Log.v(TAG, "New SurfaceTexture ID: " + entry.id());
     registerTexture(entry.id(), entry.textureWrapper());
-    addOnLowMemoryListener(entry);
+    addOnTrimMemoryListener(entry);
     return entry;
   }
 
   @Override
   public void onTrimMemory(int level) {
-    for (TextureRegistry.OnLowMemoryListener listener : onLowMemoryListeners) {
-      listener.onLowMemory(level);
+    Set<WeakReference<OnTrimMemoryListener>> listenerToBeDeleted = new HashSet<>();
+    for (WeakReference<OnTrimMemoryListener> listenerRef : onTrimMemoryListeners) {
+      final OnTrimMemoryListener listener = listenerRef.get();
+      if (listener != null) {
+        listener.onTrimMemory(level);
+      } else {
+        listenerToBeDeleted.add(listenerRef);
+      }
+    }
+
+    // Purge cleared refs lazily to avoid accumulating a lot of dead listener.
+    for (WeakReference<OnTrimMemoryListener> listenerRef : listenerToBeDeleted) {
+      onTrimMemoryListeners.remove(listenerRef);
     }
   }
 
   final class SurfaceTextureRegistryEntry
-      implements TextureRegistry.SurfaceTextureEntry, TextureRegistry.OnLowMemoryListener {
+      implements TextureRegistry.SurfaceTextureEntry, TextureRegistry.OnTrimMemoryListener {
     private final long id;
     @NonNull private final SurfaceTextureWrapper textureWrapper;
     private boolean released;
-    @Nullable private OnLowMemoryListener lowMemoryListener;
+    @Nullable private OnTrimMemoryListener trimMemoryListener;
     @Nullable private OnFrameConsumedListener frameConsumedListener;
     private final Runnable onFrameConsumed =
         new Runnable() {
@@ -181,9 +204,9 @@ public void run() {
     }
 
     @Override
-    public void onLowMemory(int level) {
-      if (lowMemoryListener != null) {
-        lowMemoryListener.onLowMemory(level);
+    public void onTrimMemory(int level) {
+      if (trimMemoryListener != null) {
+        trimMemoryListener.onTrimMemory(level);
       }
     }
 
@@ -203,7 +226,7 @@ public void onFrameAvailable(@NonNull SurfaceTexture texture) {
         };
 
     private void removeListener() {
-      removeOnLowMemoryListener(this);
+      removeOnTrimMemoryListener(this);
     }
 
     @NonNull
@@ -241,17 +264,7 @@ protected void finalize() throws Throwable {
           return;
         }
 
-        handler.post(
-            new Runnable() {
-              @Override
-              public void run() {
-                if (!flutterJNI.isAttached()) {
-                  return;
-                }
-                unregisterTexture(id);
-                removeListener();
-              }
-            });
+        handler.post(new SurfaceTextureFinalizerRunnable(id, flutterJNI));
       } finally {
         super.finalize();
       }
@@ -263,8 +276,27 @@ public void setOnFrameConsumedListener(@Nullable OnFrameConsumedListener listene
     }
 
     @Override
-    public void setOnLowMemoryListener(@Nullable OnLowMemoryListener listener) {
-      lowMemoryListener = listener;
+    public void setOnTrimMemoryListener(@Nullable OnTrimMemoryListener listener) {
+      trimMemoryListener = listener;
+    }
+  }
+
+  static final class SurfaceTextureFinalizerRunnable implements Runnable {
+    private final long id;
+    private final FlutterJNI flutterJNI;
+
+    SurfaceTextureFinalizerRunnable(long id, @NonNull FlutterJNI flutterJNI) {
+      this.id = id;
+      this.flutterJNI = flutterJNI;
+    }
+
+    @Override
+    public void run() {
+      if (!flutterJNI.isAttached()) {
+        return;
+      }
+      Log.v(TAG, "Releasing a SurfaceTexture (" + id + ").");
+      flutterJNI.unregisterTexture(id);
     }
   }
   // ------ END TextureRegistry IMPLEMENTATION ----

shell/platform/android/io/flutter/plugin/platform/PlatformViewWrapper.java

@@ -69,14 +69,15 @@ public void onFrameConsumed() {
       };
 
   private boolean shouldRecreateSurfaceForLowMemory = false;
-  private final TextureRegistry.OnLowMemoryListener lowMemoryListener =
-      new TextureRegistry.OnLowMemoryListener() {
+  private final TextureRegistry.OnTrimMemoryListener trimMemoryListener =
+      new TextureRegistry.OnTrimMemoryListener() {
         @Override
-        public void onLowMemory(int level) {
+        public void onTrimMemory(int level) {
           // When a memory pressure warning is received and the level equal {@code
           // ComponentCallbacks2.TRIM_MEMORY_COMPLETE}, the Android system release the underlying
           // surface. If we continue to use the surface (e.g., call lockHardwareCanvas), a crash
           // occurs, and we found that this crash appeared on Android10 and above.
+          // See https://github.com/flutter/flutter/issues/103870 for more details.
           //
           // Here our workaround is to recreate the surface before using it.
           if (level == TRIM_MEMORY_COMPLETE && Build.VERSION.SDK_INT >= 29) {
@@ -117,7 +118,7 @@ public PlatformViewWrapper(
       @NonNull Context context, @NonNull TextureRegistry.SurfaceTextureEntry textureEntry) {
     this(context);
     textureEntry.setOnFrameConsumedListener(frameConsumedListener);
-    textureEntry.setOnLowMemoryListener(lowMemoryListener);
+    textureEntry.setOnTrimMemoryListener(trimMemoryListener);
     setTexture(textureEntry.surfaceTexture());
   }
 

shell/platform/android/io/flutter/view/TextureRegistry.java

@@ -54,7 +54,7 @@ interface SurfaceTextureEntry {
     default void setOnFrameConsumedListener(@Nullable OnFrameConsumedListener listener) {}
 
     /** Set a listener that will be notified when a memory pressure warning was forward. */
-    default void setOnLowMemoryListener(@Nullable OnLowMemoryListener listener) {}
+    default void setOnTrimMemoryListener(@Nullable OnTrimMemoryListener listener) {}
   }
 
   /** Listener invoked when the most recent image has been consumed. */
@@ -67,8 +67,8 @@ interface OnFrameConsumedListener {
   }
 
   /** Listener invoked when a memory pressure warning was forward. */
-  interface OnLowMemoryListener {
+  interface OnTrimMemoryListener {
     /** This method will be invoked when a memory pressure warning was forward. */
-    void onLowMemory(int level);
+    void onTrimMemory(int level);
   }
 }

shell/platform/android/test/io/flutter/embedding/android/FlutterActivityAndFragmentDelegateTest.java

@@ -863,23 +863,6 @@ public void itNotifiesDartExecutorAndSendsMessageOverSystemChannelWhenToldToTrim
     verify(mockFlutterEngine.getSystemChannel(), times(6)).sendMemoryPressureWarning();
   }
 
-  @Test
-  public void itNotifiesDartExecutorAndSendsMessageOverSystemChannelWhenInformedOfLowMemory() {
-    // Create the real object that we're testing.
-    FlutterActivityAndFragmentDelegate delegate = new FlutterActivityAndFragmentDelegate(mockHost);
-
-    // --- Execute the behavior under test ---
-    // The FlutterEngine is set up in onAttach().
-    delegate.onAttach(ctx);
-
-    // Emulate the host and call the method that we expect to be forwarded.
-    delegate.onLowMemory();
-
-    // Verify that the call was forwarded to the engine.
-    verify(mockFlutterEngine.getDartExecutor(), times(1)).notifyLowMemoryWarning();
-    verify(mockFlutterEngine.getSystemChannel(), times(1)).sendMemoryPressureWarning();
-  }
-
   @Test
   public void itDestroysItsOwnEngineIfHostRequestsIt() {
     // ---- Test setup ----

shell/platform/android/test/io/flutter/embedding/engine/renderer/FlutterRendererTest.java

@@ -347,18 +347,17 @@ public void itNotifySurfaceTextureEntryWhenMemoryPressureWarning() {
     FlutterRenderer flutterRenderer = new FlutterRenderer(fakeFlutterJNI);
 
     AtomicInteger invocationCount = new AtomicInteger(0);
-    final TextureRegistry.OnLowMemoryListener listener =
-        new TextureRegistry.OnLowMemoryListener() {
+    final TextureRegistry.OnTrimMemoryListener listener =
+        new TextureRegistry.OnTrimMemoryListener() {
           @Override
-          public void onLowMemory(int level) {
+          public void onTrimMemory(int level) {
             invocationCount.incrementAndGet();
           }
         };
 
     FlutterRenderer.SurfaceTextureRegistryEntry entry =
         (FlutterRenderer.SurfaceTextureRegistryEntry) flutterRenderer.createSurfaceTexture();
-    entry.setOnLowMemoryListener(listener);
-    flutterRenderer.addOnLowMemoryListener(entry);
+    entry.setOnTrimMemoryListener(listener);
 
     // Execute the behavior under test.
     flutterRenderer.onTrimMemory(TRIM_MEMORY_COMPLETE);