Better align Emacs window management with Android task lifecycles

* java/org/gnu/emacs/EmacsActivity.java (onCreate): Permit
overriding by child classes.
(onDestroy): Minor stylistic adjustments.
(getAttachmentToken): New function.

* java/org/gnu/emacs/EmacsMultitaskActivity.java (onCreate)
(getAttachmentToken): New functions.

* java/org/gnu/emacs/EmacsWindow.java (EmacsWindow):
<attachmentToken, preserve, previouslyAttached>: New variables.
(onActivityDetached): Remove redundant isFinishing argument.
(reparentTo): Reset the foregoing fields before registering with
the window manager.

* java/org/gnu/emacs/EmacsWindowManager.java
(EmacsWindowManager): Rename from EmacsWindowAttachmentManager.
(WindowConsumer): New function getAttachmentToken.
(isWindowEligible): New function.
(registerWindowConsumer, registerWindow, removeWindowConsumer)
(detachWindow): Implement a new window management strategy on
API 29 and subsequent releases where both varieties of toplevel
window are permanently, except when reparented, bound to the
activities to which they attach, and Emacs establishes at
strategic junctures whether those activities remain present.
(getTaskToken, pruneWindows): New functions.

1 files changed, 18 insertions, 10 deletions

diff --git a/java/org/gnu/emacs/EmacsActivity.java b/java/org/gnu/emacs/EmacsActivity.java
index e380b7bfc2a..a939641a752 100644
--- a/java/org/gnu/emacs/EmacsActivity.java
+++ b/java/org/gnu/emacs/EmacsActivity.java
@@ -50,7 +50,7 @@ import android.view.WindowInsetsController;
 import android.widget.FrameLayout;
 
 public class EmacsActivity extends Activity
-  implements EmacsWindowAttachmentManager.WindowConsumer,
+  implements EmacsWindowManager.WindowConsumer,
   ViewTreeObserver.OnGlobalLayoutListener
 {
   public static final String TAG = "EmacsActivity";
@@ -218,7 +218,7 @@ public class EmacsActivity extends Activity
   }
 
   @Override
-  public final void
+  public void
   onCreate (Bundle savedInstanceState)
   {
     FrameLayout.LayoutParams params;
@@ -249,7 +249,7 @@ public class EmacsActivity extends Activity
     EmacsService.startEmacsService (this);
 
     /* Add this activity to the list of available activities.  */
-    EmacsWindowAttachmentManager.MANAGER.registerWindowConsumer (this);
+    EmacsWindowManager.MANAGER.registerWindowConsumer (this);
 
     /* Start observing global layout changes between Jelly Bean and Q.
        This is required to restore the fullscreen state whenever the
@@ -326,16 +326,16 @@ public class EmacsActivity extends Activity
   public final void
   onDestroy ()
   {
-    EmacsWindowAttachmentManager manager;
-    boolean isMultitask;
+    EmacsWindowManager manager;
+    boolean isMultitask, reallyFinishing;
 
-    manager = EmacsWindowAttachmentManager.MANAGER;
+    manager = EmacsWindowManager.MANAGER;
 
     /* The activity will die shortly hereafter.  If there is a window
        attached, close it now.  */
     isMultitask = this instanceof EmacsMultitaskActivity;
-    manager.removeWindowConsumer (this, (isMultitask
-					 || isReallyFinishing ()));
+    reallyFinishing = isReallyFinishing ();
+    manager.removeWindowConsumer (this, isMultitask || reallyFinishing);
     focusedActivities.remove (this);
     invalidateFocus (2);
 
@@ -383,7 +383,7 @@ public class EmacsActivity extends Activity
   {
     isPaused = true;
 
-    EmacsWindowAttachmentManager.MANAGER.noticeIconified (this);
+    EmacsWindowManager.MANAGER.noticeIconified (this);
     super.onPause ();
   }
 
@@ -394,7 +394,7 @@ public class EmacsActivity extends Activity
     isPaused = false;
     timeOfLastInteraction = 0;
 
-    EmacsWindowAttachmentManager.MANAGER.noticeDeiconified (this);
+    EmacsWindowManager.MANAGER.noticeDeiconified (this);
     super.onResume ();
   }
 
@@ -538,6 +538,14 @@ public class EmacsActivity extends Activity
 
     EmacsNative.sendNotificationAction (tag, action);
   }
+
+  @Override
+  public long
+  getAttachmentToken ()
+  {
+    return -1; /* This is overridden by EmacsMultitaskActivity.  */
+  }
+
 
 
   @Override