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, 30 insertions, 23 deletions

diff --git a/java/org/gnu/emacs/EmacsWindow.java b/java/org/gnu/emacs/EmacsWindow.java
index 2baede1d2d0..9b444c3f144 100644
--- a/java/org/gnu/emacs/EmacsWindow.java
+++ b/java/org/gnu/emacs/EmacsWindow.java
@@ -112,7 +112,7 @@ public final class EmacsWindow extends EmacsHandleObject
   private SparseArray<Coordinate> pointerMap;
 
   /* The window consumer currently attached, if it exists.  */
-  private EmacsWindowAttachmentManager.WindowConsumer attached;
+  private EmacsWindowManager.WindowConsumer attached;
 
   /* The window background scratch GC.  foreground is always the
      window background.  */
@@ -159,6 +159,16 @@ public final class EmacsWindow extends EmacsHandleObject
      values are -1 if no drag and drop operation is under way.  */
   private int dndXPosition, dndYPosition;
 
+  /* Identifier binding this window to the activity created for it, or
+     -1 if the window should be attached to system-created activities
+     (i.e. the activity launched by the system at startup).  Value is
+     meaningless under API level 29 and earlier.  */
+  public long attachmentToken;
+
+  /* Whether this window should be preserved during window pruning,
+     and whether this window has previously been attached to a task.  */
+  public boolean preserve, previouslyAttached;
+
   public
   EmacsWindow (short handle, final EmacsWindow parent, int x, int y,
 	       int width, int height, boolean overrideRedirect)
@@ -255,12 +265,12 @@ public final class EmacsWindow extends EmacsHandleObject
 	run ()
 	{
 	  ViewManager parent;
-	  EmacsWindowAttachmentManager manager;
+	  EmacsWindowManager manager;
 
 	  if (EmacsActivity.focusedWindow == EmacsWindow.this)
 	    EmacsActivity.focusedWindow = null;
 
-	  manager = EmacsWindowAttachmentManager.MANAGER;
+	  manager = EmacsWindowManager.MANAGER;
 	  view.setVisibility (View.GONE);
 
 	  /* If the window manager is set, use that instead.  */
@@ -281,12 +291,12 @@ public final class EmacsWindow extends EmacsHandleObject
   }
 
   public void
-  setConsumer (EmacsWindowAttachmentManager.WindowConsumer consumer)
+  setConsumer (EmacsWindowManager.WindowConsumer consumer)
   {
     attached = consumer;
   }
 
-  public EmacsWindowAttachmentManager.WindowConsumer
+  public EmacsWindowManager.WindowConsumer
   getAttachedConsumer ()
   {
     return attached;
@@ -420,7 +430,7 @@ public final class EmacsWindow extends EmacsHandleObject
 	    public void
 	    run ()
 	    {
-	      EmacsWindowAttachmentManager manager;
+	      EmacsWindowManager manager;
 	      WindowManager windowManager;
 	      Activity ctx;
 	      Object tem;
@@ -431,7 +441,7 @@ public final class EmacsWindow extends EmacsHandleObject
 
 	      if (!overrideRedirect)
 		{
-		  manager = EmacsWindowAttachmentManager.MANAGER;
+		  manager = EmacsWindowManager.MANAGER;
 
 		  /* If parent is the root window, notice that there are new
 		     children available for interested activities to pick
@@ -527,9 +537,9 @@ public final class EmacsWindow extends EmacsHandleObject
 	public void
 	run ()
 	{
-	  EmacsWindowAttachmentManager manager;
+	  EmacsWindowManager manager;
 
-	  manager = EmacsWindowAttachmentManager.MANAGER;
+	  manager = EmacsWindowManager.MANAGER;
 
 	  view.setVisibility (View.GONE);
 
@@ -809,20 +819,13 @@ public final class EmacsWindow extends EmacsHandleObject
     EmacsActivity.invalidateFocus (gainFocus ? 6 : 5);
   }
 
-  /* Notice that the activity has been detached or destroyed.
-
-     ISFINISHING is set if the activity is not the main activity, or
-     if the activity was not destroyed in response to explicit user
-     action.  */
+  /* Notice that the activity (or its task) has been detached or
+     destroyed by explicit user action.  */
 
   public void
-  onActivityDetached (boolean isFinishing)
+  onActivityDetached ()
   {
-    /* Destroy the associated frame when the activity is detached in
-       response to explicit user action.  */
-
-    if (isFinishing)
-      EmacsNative.sendWindowAction (this.handle, 0);
+    EmacsNative.sendWindowAction (this.handle, 0);
   }
 
 
@@ -1312,13 +1315,17 @@ public final class EmacsWindow extends EmacsHandleObject
 	public void
 	run ()
 	{
-	  EmacsWindowAttachmentManager manager;
+	  EmacsWindowManager manager;
 	  ViewManager parent;
 
 	  /* First, detach this window if necessary.  */
-	  manager = EmacsWindowAttachmentManager.MANAGER;
+	  manager = EmacsWindowManager.MANAGER;
 	  manager.detachWindow (EmacsWindow.this);
 
+	  /* Reset window management state.  */
+	  previouslyAttached = false;
+	  attachmentToken = false;
+
 	  /* Also unparent this view.  */
 
 	  /* If the window manager is set, use that instead.  */
@@ -1858,7 +1865,7 @@ public final class EmacsWindow extends EmacsHandleObject
   public void
   recreateActivity ()
   {
-    final EmacsWindowAttachmentManager.WindowConsumer attached;
+    final EmacsWindowManager.WindowConsumer attached;
 
     attached = this.attached;