Dismiss Android Back key events that are canceled

* java/org/gnu/emacs/EmacsWindow.java (onKeyDown): Disregard
KEYCODE_BACK events.
(onKeyUp): If the event is KEYCODE_BACK, deliver the disregarded
key press event, unless FLAG_CANCELED is set.

1 files changed, 31 insertions, 6 deletions

diff --git a/java/org/gnu/emacs/EmacsWindow.java b/java/org/gnu/emacs/EmacsWindow.java
index 013f09cb756..7d161fdcf88 100644
--- a/java/org/gnu/emacs/EmacsWindow.java
+++ b/java/org/gnu/emacs/EmacsWindow.java
@@ -648,6 +648,21 @@ public final class EmacsWindow extends EmacsHandleObject
     long serial;
     String characters;
 
+    if (keyCode == KeyEvent.KEYCODE_BACK)
+      {
+        /* New Android systems display Back navigation buttons on a
+           row of virtual buttons at the bottom of the screen.  These
+           buttons function much as physical buttons do, in that key
+           down events are produced when a finger taps them, even if
+           the finger is not ultimately released after the OS's
+           gesture navigation is activated.
+
+           Deliver onKeyDown events in onKeyUp instead, so as not to
+           navigate backwards during gesture navigation.  */
+
+        return;
+      }
+
     state = eventModifiers (event);
 
     /* Ignore meta-state understood by Emacs for now, or key presses
@@ -677,7 +692,7 @@ public final class EmacsWindow extends EmacsHandleObject
   public void
   onKeyUp (int keyCode, KeyEvent event)
   {
-    int state, state_1;
+    int state, state_1, unicode_char;
     long time;
 
     /* Compute the event's modifier mask.  */
@@ -691,11 +706,21 @@ public final class EmacsWindow extends EmacsHandleObject
       = state & ~(KeyEvent.META_ALT_MASK | KeyEvent.META_CTRL_MASK
                   | KeyEvent.META_SYM_ON | KeyEvent.META_META_MASK);
 
-    EmacsNative.sendKeyRelease (this.handle,
-                                event.getEventTime (),
-                                state, keyCode,
-                                getEventUnicodeChar (event,
-                                                     state_1));
+    unicode_char = getEventUnicodeChar (event, state_1);
+
+    if (keyCode == KeyEvent.KEYCODE_BACK)
+      {
+        /* If the key press's been canceled, return immediately.  */
+
+        if ((event.getFlags () & KeyEvent.FLAG_CANCELED) != 0)
+          return;
+
+        EmacsNative.sendKeyPress (this.handle, event.getEventTime (),
+                                  state, keyCode, unicode_char);
+      }
+
+    EmacsNative.sendKeyRelease (this.handle, event.getEventTime (),
+                                state, keyCode, unicode_char);
 
     if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN)
       {