Clear Activity after Being Destroyed

Summary:
[Reported in the support request](https://fb.workplace.com/groups/flippersupport/posts/1237466586733997/), Activity object is held by ObjectTracker even though the Activity is destroyed. This, in this case, caused strict mode in Portal app to forcibly terminate.

This diff tried to remove activities from the reference holder.

Reviewed By: passy

Differential Revision: D31828290

fbshipit-source-id: aad7e8d7ba14069f8dd7c654a3604d482d85e110

android/src/main/java/com/facebook/flipper/plugins/inspector/ApplicationWrapper.java

@@ -27,11 +27,16 @@ public class ApplicationWrapper implements Application.ActivityLifecycleCallback
     void onActivityStackChanged(List<Activity> stack);
   }
 
+  public interface ActivityDestroyedListener {
+    void onActivityDestroyed(Activity activity);
+  }
+
   private final Application mApplication;
   private final AndroidRootResolver mAndroidRootsResolver;
   private final List<WeakReference<Activity>> mActivities;
   private final Handler mHandler;
   private ActivityStackChangedListener mListener;
+  private ActivityDestroyedListener mActivityDestroyedListener;
 
   public ApplicationWrapper(Application application) {
     mApplication = application;
@@ -66,6 +71,10 @@ public class ApplicationWrapper implements Application.ActivityLifecycleCallback
   public void onActivityDestroyed(Activity activity) {
     final Iterator<WeakReference<Activity>> activityIterator = mActivities.iterator();
 
+    if (mActivityDestroyedListener != null) {
+      mActivityDestroyedListener.onActivityDestroyed(activity);
+    }
+
     while (activityIterator.hasNext()) {
       if (activityIterator.next().get() == activity) {
         activityIterator.remove();
@@ -84,6 +93,10 @@ public class ApplicationWrapper implements Application.ActivityLifecycleCallback
     mListener = listener;
   }
 
+  public void setActivityDestroyedListener(ActivityDestroyedListener listener) {
+    mActivityDestroyedListener = listener;
+  }
+
   public Application getApplication() {
     return mApplication;
   }

android/src/main/java/com/facebook/flipper/plugins/inspector/InspectorFlipperPlugin.java

@@ -7,8 +7,10 @@
 
 package com.facebook.flipper.plugins.inspector;
 
+import android.app.Activity;
 import android.app.Application;
 import android.content.Context;
+import android.util.Log;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.accessibility.AccessibilityEvent;
@@ -29,6 +31,7 @@ import java.util.Map;
 import javax.annotation.Nullable;
 
 public class InspectorFlipperPlugin implements FlipperPlugin {
+  private static final String TAG = "ContextDescriptor";
 
   private ApplicationWrapper mApplication;
   private DescriptorMapping mDescriptorMapping;
@@ -91,7 +94,7 @@ public class InspectorFlipperPlugin implements FlipperPlugin {
   // Package visible for testing
   InspectorFlipperPlugin(
       ApplicationWrapper wrapper,
-      DescriptorMapping descriptorMapping,
+      final DescriptorMapping descriptorMapping,
       @Nullable List<ExtensionCommand> extensions) {
     mDescriptorMapping = descriptorMapping;
 
@@ -99,6 +102,29 @@ public class InspectorFlipperPlugin implements FlipperPlugin {
     mApplication = wrapper;
     mExtensionCommands = extensions;
     mShowLithoAccessibilitySettings = false;
+
+    mApplication.setActivityDestroyedListener(
+        new ApplicationWrapper.ActivityDestroyedListener() {
+          private final DescriptorMapping mCallbackDescriptorMapping = mDescriptorMapping;
+          private final ObjectTracker mCallbackObjectTracker = mObjectTracker;
+
+          @Override
+          public void onActivityDestroyed(Activity activity) {
+            try {
+              final NodeDescriptor<Activity> activityDescriptor =
+                  (NodeDescriptor<Activity>)
+                      mCallbackDescriptorMapping.descriptorForClass(Activity.class);
+              if (activityDescriptor == null || mCallbackObjectTracker == null) {
+                return;
+              }
+              String activityId = activityDescriptor.getId(activity);
+              mCallbackObjectTracker.remove(activityId);
+            } catch (Exception e) {
+              // Ignore if there is an error
+              Log.d(TAG, "Cannot remove activity from ObjectTracker: " + e.getMessage());
+            }
+          }
+        });
   }
 
   @Override

android/src/main/java/com/facebook/flipper/plugins/inspector/ObjectTracker.java

@@ -40,6 +40,10 @@ public class ObjectTracker {
     mObjects.clear();
   }
 
+  public void remove(String id) {
+    mObjects.remove(id);
+  }
+
   public boolean contains(String id) {
     return mObjects.containsKey(id);
   }