Port new Android window management strategy to Android 5.0

* doc/emacs/android.texi (Android Windowing): Revise to match.

* java/org/gnu/emacs/EmacsWindowManager.java (registerWindow)
(removeWindowConsumer, pruneWindows): Decrease minimum API for
monitoring of tasks to Android 5.0.
(getTaskToken): Ignore misleading documentation and access
baseIntent by way of RecentTaskInfo.

1 files changed, 28 insertions, 22 deletions

diff --git a/java/org/gnu/emacs/EmacsWindowManager.java b/java/org/gnu/emacs/EmacsWindowManager.java
index 41ea3a15809..22629cad329 100644
--- a/java/org/gnu/emacs/EmacsWindowManager.java
+++ b/java/org/gnu/emacs/EmacsWindowManager.java
@@ -23,9 +23,9 @@ import java.util.ArrayList;
 import java.util.List;
 
 import android.app.ActivityManager.AppTask;
+import android.app.ActivityManager.RecentTaskInfo;
 import android.app.ActivityManager;
 import android.app.ActivityOptions;
-import android.app.TaskInfo;
 
 import android.content.Context;
 import android.content.Intent;
@@ -60,7 +60,7 @@ import android.util.Log;
      getAttachmentToken ()
 
    should return a token uniquely identifying a consumer, which, on API
-   29 and up, enables attributing the tasks of activities to the windows
+   21 and up, enables attributing the tasks of activities to the windows
    for which they were created, and with that, consistent interaction
    between user-visible window state and their underlying frames.  */
 
@@ -182,7 +182,21 @@ public final class EmacsWindowManager
     /* Intent.FLAG_ACTIVITY_NEW_DOCUMENT is lamentably unavailable on
        older systems than Lolipop.  */
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP)
-      intent.addFlags (Intent.FLAG_ACTIVITY_NEW_DOCUMENT);
+      {
+        intent.addFlags (Intent.FLAG_ACTIVITY_NEW_DOCUMENT);
+
+        /* Bind this window to the activity in advance, i.e., before its
+           creation, so that its ID will be recorded in the RecentTasks
+           list.  */
+        token = ++nextActivityToken;
+      }
+    else
+      /* APIs required for linking activities to windows are not
+         available in earlier Android versions.  */
+      token = -2;
+
+    window.attachmentToken = token;
+    intent.putExtra (ACTIVITY_TOKEN, token);
 
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N)
       EmacsService.SERVICE.startActivity (intent);
@@ -191,19 +205,6 @@ public final class EmacsWindowManager
         /* Specify the desired window size.  */
         options = ActivityOptions.makeBasic ();
         options.setLaunchBounds (window.getGeometry ());
-
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
-          /* Bind this window to the activity in advance, i.e., before
-             its creation, so that its ID will be recorded in the
-             RecentTasks list.  */
-          token = ++nextActivityToken;
-        else
-          /* APIs required for linking activities to windows are not
-             available in earlier Android versions.  */
-          token = -2;
-
-        window.attachmentToken = token;
-        intent.putExtra (ACTIVITY_TOKEN, token);
         EmacsService.SERVICE.startActivity (intent, options.toBundle ());
       }
 
@@ -228,7 +229,7 @@ public final class EmacsWindowManager
            the system-started task.  */
         if (isFinishing
             && (!(consumer instanceof EmacsMultitaskActivity)
-                || Build.VERSION.SDK_INT < Build.VERSION_CODES.Q))
+                || Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP))
           window.onActivityDetached ();
       }
 
@@ -297,12 +298,17 @@ public final class EmacsWindowManager
   private static long
   getTaskToken (AppTask task)
   {
-    TaskInfo info;
+    RecentTaskInfo info;
+
+    info = task.getTaskInfo ();
 
-    info = (TaskInfo) task.getTaskInfo ();
+    /* baseIntent is a member of info's superclass, TaskInfo, on Android
+       10 and later.  Prior to this release, it had been a member of
+       RecentTaskInfo since SDK 1, and whatever the misleading
+       documentation might suggest, a reference to `baseIntent' through
+       TaskInfo is just as good a reference to RecentTaskInfo.  */
     return (info.baseIntent != null
-            ? info.baseIntent.getLongExtra (ACTIVITY_TOKEN,
-                                            -1l)
+            ? info.baseIntent.getLongExtra (ACTIVITY_TOKEN, -1l)
             : 0);
   }
 
@@ -319,7 +325,7 @@ public final class EmacsWindowManager
     long taskToken;
     boolean set;
 
-    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q
+    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP
         || EmacsService.SERVICE == null)
       return;