Make FlutterFragment usable without requiring it to be attached to an Android Activity. (#27332)

Author: ajmalk

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

@@ -276,23 +276,23 @@ View onCreateView(
     if (host.getRenderMode() == RenderMode.surface) {
       FlutterSurfaceView flutterSurfaceView =
           new FlutterSurfaceView(
-              host.getActivity(), host.getTransparencyMode() == TransparencyMode.transparent);
+              host.getContext(), host.getTransparencyMode() == TransparencyMode.transparent);
 
       // Allow our host to customize FlutterSurfaceView, if desired.
       host.onFlutterSurfaceViewCreated(flutterSurfaceView);
 
       // Create the FlutterView that owns the FlutterSurfaceView.
-      flutterView = new FlutterView(host.getActivity(), flutterSurfaceView);
+      flutterView = new FlutterView(host.getContext(), flutterSurfaceView);
     } else {
-      FlutterTextureView flutterTextureView = new FlutterTextureView(host.getActivity());
+      FlutterTextureView flutterTextureView = new FlutterTextureView(host.getContext());
 
       flutterTextureView.setOpaque(host.getTransparencyMode() == TransparencyMode.opaque);
 
       // Allow our host to customize FlutterSurfaceView, if desired.
       host.onFlutterTextureViewCreated(flutterTextureView);
 
       // Create the FlutterView that owns the FlutterTextureView.
-      flutterView = new FlutterView(host.getActivity(), flutterTextureView);
+      flutterView = new FlutterView(host.getContext(), flutterTextureView);
     }
 
     // Add listener to be notified when Flutter renders its first frame.

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

@@ -378,21 +378,31 @@ public void itDoesNotAttachFlutterToTheActivityIfNotDesired() {
     // Declare that the host does NOT want Flutter to attach to the surrounding Activity.
     when(mockHost.shouldAttachEngineToActivity()).thenReturn(false);
 
+    // getActivity() returns null if the activity is not attached
+    when(mockHost.getActivity()).thenReturn(null);
+
     // Create the real object that we're testing.
     FlutterActivityAndFragmentDelegate delegate = new FlutterActivityAndFragmentDelegate(mockHost);
 
     // --- Execute the behavior under test ---
     // Flutter is attached to the surrounding Activity in onAttach.
     delegate.onAttach(RuntimeEnvironment.application);
 
-    // Verify that the ActivityControlSurface was NOT told to attach to an Activity.
-    verify(mockFlutterEngine.getActivityControlSurface(), never())
-        .attachToActivity(any(Activity.class), any(Lifecycle.class));
+    // Make sure all of the other lifecycle methods can run safely as well
+    // without a valid Activity
+    delegate.onCreateView(null, null, null);
+    delegate.onStart();
+    delegate.onResume();
+    delegate.onPause();
+    delegate.onStop();
+    delegate.onDestroyView();
 
     // Flutter is detached from the surrounding Activity in onDetach.
     delegate.onDetach();
 
-    // Verify that the ActivityControlSurface was NOT told to detach from the Activity.
+    // Verify that the ActivityControlSurface was NOT told to attach or detach to an Activity.
+    verify(mockFlutterEngine.getActivityControlSurface(), never())
+        .attachToActivity(any(Activity.class), any(Lifecycle.class));
     verify(mockFlutterEngine.getActivityControlSurface(), never()).detachFromActivity();
   }