Improve appearance of the Android preferences screen

* .gitignore: Add org/gnu/emacs/R.java.
* cross/Makefile.in (top_builddir): Include verbose.mk.  Rewrite
rules to print nice looking statements.
* doc/emacs/android.texi (Android, Android Startup)
(Android Environment, Android Windowing, Android Fonts):
* doc/emacs/emacs.texi (Top): Add an extra ``Android
Troubleshooting'' node and move troubleshooting details there.
* java/Makefile.in: Generate R.java; improve appearance by using
verbose.mk.

* java/org/gnu/emacs/EmacsPreferencesActivity.java: Reimplement
in terms of PreferencesActivity.
* java/org/gnu/emacs/EmacsView.java (handleDirtyBitmap): Avoid
flicker.
* java/res/xml/preferences.xml: New file.
* src/verbose.mk.in (AM_V_AAPT, AM_V_SILENT): New variables.

4 files changed, 171 insertions, 89 deletions

diff --git a/java/Makefile.in b/java/Makefile.in
index 155754b59d2..fc0d23980e4 100644
--- a/java/Makefile.in
+++ b/java/Makefile.in
@@ -54,18 +54,33 @@ JARSIGNER_FLAGS =
 endif
 
 SIGN_EMACS = -keystore emacs.keystore -storepass emacs1 $(JARSIGNER_FLAGS)
-SIGN_EMACS_V2 = sign --v2-signing-enabled --ks emacs.keystore \
+SIGN_EMACS_V2 = sign --v2-signing-enabled --ks emacs.keystore   \
         --debuggable-apk-permitted --ks-pass pass:emacs1
 
-JAVA_FILES = $(wildcard $(srcdir)/org/gnu/emacs/*.java)
-RESOURCE_FILES = $(wildcard $(srcdir)/res/drawable/*)
-CLASS_FILES = $(foreach file,$(JAVA_FILES),$(basename $(file)).class)
+JAVA_FILES := $(wildcard $(srcdir)/org/gnu/emacs/*.java)
+RESOURCE_FILES := $(foreach file,$(wildcard $(srcdir)/res/*),   \
+                    $(wildcard $(file)/*))
+
+# R.java is a file generated by the `aapt' utility containing
+# constants that can then be used to locate ``resource identifiers''.
+# It is not a regular file and should not be compiled as Java source
+# code.  Instead, it is automatically included by the Java compiler.
+RESOURCE_FILE := $(srcdir)/org/gnu/emacs/R.java
+
+# CLASS_FILES is what should actually be built and included in the
+# resulting Emacs executable.  The Java compiler might generate more
+# than one class file for each source file, so this only serves as a
+# list of dependencies for Make.
+CLASS_FILES := $(foreach file,$(JAVA_FILES),$(basename $(file)).class)
+
+# Remove RESOURCE_FILE from JAVA_FILES, if it is already present.
+JAVA_FILES := $(filter-out $(RESOURCE_FILE),$(JAVA_FILES))
 
 # Compute the name for the Emacs application package.  This should be:
 # emacs-<version>-<min-sdk>-<abi>.apk
 
-ANDROID_MIN_SDK = @ANDROID_MIN_SDK@
-APK_NAME = emacs-$(version)-$(ANDROID_MIN_SDK)-$(ANDROID_ABI).apk
+ANDROID_MIN_SDK := @ANDROID_MIN_SDK@
+APK_NAME := emacs-$(version)-$(ANDROID_MIN_SDK)-$(ANDROID_ABI).apk
 
 # How this stuff works.
 
@@ -113,19 +128,25 @@ include $(top_builddir)/cross/ndk-build/ndk-build.mk
 $(libsrc)/asset-directory-tool:
         $(MAKE) -C $(libsrc) $(notdir $@)
 
-emacs.apk-in: $(CROSS_BINS) $(CROSS_LIBS) $(libsrc)/asset-directory-tool \
-  AndroidManifest.xml $(NDK_BUILD_SHARED) $(RESOURCE_FILES)
+# install_tmp is a directory used to generate emacs.apk-in.
+# That is then packaged into $(APK_NAME).
+
+.PHONY: install_temp install_temp/assets/directory-tree
+install_temp: $(CROSS_BINS) $(CROSS_LIBS) $(NDK_BUILD_SHARED)   \
+  $(RESOURCE_FILES)
+        $(AM_V_GEN)
 # Make the working directory for this stuff
-        rm -rf install_temp
-        mkdir -p install_temp/lib/$(ANDROID_ABI)
-        mkdir -p install_temp/assets/etc
-        mkdir -p install_temp/assets/lisp
-        mkdir -p install_temp/assets/info
+        $(AM_V_SILENT) rm -rf install_temp
+        $(AM_V_SILENT) mkdir -p install_temp/lib/$(ANDROID_ABI)
+        $(AM_V_SILENT) mkdir -p install_temp/assets/etc
+        $(AM_V_SILENT) mkdir -p install_temp/assets/lisp
+        $(AM_V_SILENT) mkdir -p install_temp/assets/info
 # Install architecture independents to assets/etc and assets/lisp
-        cp -r $(top_builddir)/lisp install_temp/assets
-        cp -r $(top_builddir)/etc install_temp/assets
-        cp -r $(top_builddir)/info install_temp/assets
+        $(AM_V_SILENT) cp -r $(top_builddir)/lisp install_temp/assets
+        $(AM_V_SILENT) cp -r $(top_builddir)/etc install_temp/assets
+        $(AM_V_SILENT) cp -r $(top_builddir)/info install_temp/assets
 # Remove undesirable files from those directories.
+        $(AM_V_SILENT)                                          \
         for subdir in `find install_temp -type d -print`; do    \
           chmod a+rx $${subdir} ;                               \
           rm -rf $${subdir}/.gitignore ;                        \
@@ -139,34 +160,44 @@ emacs.apk-in: $(CROSS_BINS) $(CROSS_LIBS) $(libsrc)/asset-directory-tool \
           rm -rf $${subdir}/Makefile;                           \
         done
 # Generate the directory tree for those directories.
-        $(libsrc)/asset-directory-tool install_temp/assets      \
-          install_temp/assets/directory-tree
 # Install architecture dependents to lib/$(ANDROID_ABI).  This
 # perculiar naming scheme is required to make Android preserve these
 # binaries upon installation.
+        $(AM_V_SILENT)                                                          \
         for file in $(CROSS_BINS); do                                           \
           if [ -x $$file ]; then                                                \
             filename=`basename $$file`;                                         \
             cp -f $$file install_temp/lib/$(ANDROID_ABI)/lib$${filename}.so;    \
           fi                                                                    \
         done
+        $(AM_V_SILENT)                                          \
         for file in $(CROSS_LIBS); do                           \
           if [ -x $$file ]; then                                \
             cp -f $$file install_temp/lib/$(ANDROID_ABI);       \
           fi                                                    \
         done
 ifneq ($(NDK_BUILD_SHARED),)
-        cp -f $(NDK_BUILD_SHARED) install_temp/lib/$(ANDROID_ABI)
+        $(AM_V_SILENT) cp -f $(NDK_BUILD_SHARED) \
+          install_temp/lib/$(ANDROID_ABI)
 endif
+
+install_temp/assets/directory-tree: $(libsrc)/asset-directory-tool install_temp
+        $(AM_V_GEN) $(libsrc)/asset-directory-tool install_temp/assets \
+          install_temp/assets/directory-tree
+
+emacs.apk-in: install_temp install_temp/assets/directory-tree \
+        AndroidManifest.xml
 # Package everything.  Specifying the assets on this command line is
 # necessary for AAssetManager_getNextFileName to work on old versions
-# of Android.  Make sure not to generate R.java, as it's not required
-# by Emacs.
-        $(AAPT) package -I "$(ANDROID_JAR)" -F $@ -f    \
-          -M AndroidManifest.xml -A install_temp/assets \
+# of Android.  Make sure not to generate R.java, as it's already been
+# generated.
+        $(AM_V_AAPT) $(AAPT) p -I "$(ANDROID_JAR)" -F $@   \
+          -f -M AndroidManifest.xml -A install_temp/assets \
           -S res -J install_temp
-        pushd install_temp; $(AAPT) add ../$@ `find lib -type f`; popd
-        rm -rf install_temp
+        $(AM_V_SILENT) pushd install_temp &> /dev/null; \
+          $(AAPT) add ../$@ `find lib -type f`;         \
+        popd &> /dev/null
+        $(AM_V_SILENT) rm -rf install_temp
 
 # Makefile itself.
 .PRECIOUS: ../config.status Makefile
@@ -180,6 +211,14 @@ AndroidManifest.xml: $(top_srcdir)/configure.ac $(top_srcdir)/m4/*.m4 \
   AndroidManifest.xml.in
         pushd ..; ./config.status java/AndroidManifest.xml; popd
 
+# R.java:
+$(RESOURCE_FILE): $(RESOURCE_FILES)
+        $(AM_V_GEN) $(AAPT) p -I "$(ANDROID_JAR)" -f \
+          -J $(dir $@) -M AndroidManifest.xml -S res
+
+# Make all class files depend on R.java being built.
+$(CLASS_FILES): $(RESOURCE_FILE)
+
 .SUFFIXES: .java .class
 .java.class &:
         $(AM_V_JAVAC) $(JAVAC) $(JAVAFLAGS) $<
@@ -199,17 +238,18 @@ classes.dex: $(CLASS_FILES)
 .PHONY: clean maintainer-clean
 
 $(APK_NAME): classes.dex emacs.apk-in emacs.keystore
-        cp -f emacs.apk-in $@.unaligned
-        $(AAPT) add $@.unaligned classes.dex
-        $(JARSIGNER) $(SIGN_EMACS) $@.unaligned "Emacs keystore"
-        $(ZIPALIGN) -f 4 $@.unaligned $@
+        $(AM_V_GEN)
+        $(AM_V_SILENT) cp -f emacs.apk-in $@.unaligned
+        $(AM_V_SILENT) $(AAPT) add $@.unaligned classes.dex
+        $(AM_V_SILENT) $(JARSIGNER) $(SIGN_EMACS) $@.unaligned "Emacs keystore"
+        $(AM_V_SILENT) $(ZIPALIGN) -f 4 $@.unaligned $@
 # Signing must happen after alignment!
-        $(APKSIGNER) $(SIGN_EMACS_V2) $@
-        rm -f $@.unaligned *.idsig
+        $(AM_V_SILENT) $(APKSIGNER) $(SIGN_EMACS_V2) $@
+        $(AM_V_SILENT) rm -f $@.unaligned *.idsig
 
 clean:
         rm -f *.apk emacs.apk-in *.dex *.unaligned *.class *.idsig
-        rm -rf install-temp
+        rm -rf install-temp $(RESOURCE_FILE)
         find . -name '*.class' -delete
 
 maintainer-clean distclean bootstrap-clean: clean
diff --git a/java/org/gnu/emacs/EmacsPreferencesActivity.java b/java/org/gnu/emacs/EmacsPreferencesActivity.java
index 6cef7c37516..85639fe9236 100644
--- a/java/org/gnu/emacs/EmacsPreferencesActivity.java
+++ b/java/org/gnu/emacs/EmacsPreferencesActivity.java
@@ -22,27 +22,28 @@ package org.gnu.emacs;
 import java.io.File;
 
 import android.app.Activity;
+
 import android.content.Intent;
+
 import android.os.Bundle;
 import android.os.Build;
-import android.view.View;
-import android.view.ViewGroup.LayoutParams;
-import android.widget.LinearLayout;
-import android.widget.TextView;
 
-import android.R;
+import android.widget.Toast;
+
+import android.preference.*;
 
 /* This module provides a ``preferences'' display for Emacs.  It is
    supposed to be launched from inside the Settings application to
    perform various actions, such as starting Emacs with the ``-Q''
    option, which would not be possible otherwise, as there is no
-   command line on Android.  */
+   command line on Android.
 
-public class EmacsPreferencesActivity extends Activity
-{
-  /* The linear layout associated with the activity.  */
-  private LinearLayout layout;
+   Android provides a preferences activity, but it is deprecated.
+   Unfortunately, there is no alternative that looks the same way.  */
 
+@SuppressWarnings ("deprecation")
+public class EmacsPreferencesActivity extends PreferenceActivity
+{
   /* Restart Emacs with -Q.  Call EmacsThread.exit to kill Emacs now, and
      tell the system to EmacsActivity with some parameters later.  */
 
@@ -59,72 +60,82 @@ public class EmacsPreferencesActivity extends Activity
     System.exit (0);
   }
 
+  /* Erase Emacs's dump file.  */
+
+  private void
+  eraseDumpFile ()
+  {
+    String wantedDumpFile;
+    File file;
+    Toast toast;
+
+    wantedDumpFile = ("emacs-" + EmacsNative.getFingerprint ()
+                      + ".pdmp");
+    file = new File (getFilesDir (), wantedDumpFile);
+
+    if (file.exists ())
+      file.delete ();
+
+    /* Make sure to clear EmacsApplication.dumpFileName, or
+       starting Emacs without restarting this program will
+       make Emacs try to load a nonexistent dump file.  */
+    EmacsApplication.dumpFileName = null;
+
+    /* Display a message stating that the dump file has been
+       erased.  */
+    toast = Toast.makeText (this, "Dump file removed",
+                            Toast.LENGTH_SHORT);
+    toast.show ();
+  }
+
   @Override
   public void
   onCreate (Bundle savedInstanceState)
   {
-    LinearLayout layout;
-    TextView textView;
-    LinearLayout.LayoutParams params;
-    int resid;
+    Preference tem;
+    Preference.OnPreferenceClickListener listener;
 
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP)
-      setTheme (R.style.Theme_DeviceDefault_Settings);
+      setTheme (android.R.style.Theme_DeviceDefault_Settings);
     else if (Build.VERSION.SDK_INT
              >= Build.VERSION_CODES.ICE_CREAM_SANDWICH)
-      setTheme (R.style.Theme_DeviceDefault);
+      setTheme (android.R.style.Theme_DeviceDefault);
+
+    /* This must come before using any preference APIs.  */
+    super.onCreate (savedInstanceState);
 
-    layout = new LinearLayout (this);
-    layout.setOrientation (LinearLayout.VERTICAL);
-    setContentView (layout);
+    /* Add preferences from the XML file where they are defined.  */
+    addPreferencesFromResource (R.xml.preferences);
 
-    textView = new TextView (this);
-    textView.setPadding (8, 20, 20, 8);
+    /* Now, set up on click handlers for each of the preferences
+       items.  */
 
-    params = new LinearLayout.LayoutParams (LayoutParams.MATCH_PARENT,
-                                            LayoutParams.WRAP_CONTENT);
-    textView.setLayoutParams (params);
-    textView.setText ("(Re)start Emacs with -Q");
-    textView.setOnClickListener (new View.OnClickListener () {
+    tem = findPreference ("start_quick");
+
+    listener = new Preference.OnPreferenceClickListener () {
         @Override
-        public void
-        onClick (View view)
+        public boolean
+        onPreferenceClick (Preference preference)
         {
           startEmacsQ ();
+          return true;
         }
-      });
-    layout.addView (textView);
+      };
+
+    tem.setOnPreferenceClickListener (listener);
 
-    textView = new TextView (this);
-    textView.setPadding (8, 20, 20, 8);
+    tem = findPreference ("erase_dump");
 
-    params = new LinearLayout.LayoutParams (LayoutParams.MATCH_PARENT,
-                                            LayoutParams.WRAP_CONTENT);
-    textView.setLayoutParams (params);
-    textView.setText ("Erase dump file");
-    textView.setOnClickListener (new View.OnClickListener () {
+    listener = new Preference.OnPreferenceClickListener () {
         @Override
-        public void
-        onClick (View view)
+        public boolean
+        onPreferenceClick (Preference preference)
         {
-          String wantedDumpFile;
-          File file;
-
-          wantedDumpFile = ("emacs-" + EmacsNative.getFingerprint ()
-                            + ".pdmp");
-          file = new File (getFilesDir (), wantedDumpFile);
-
-          if (file.exists ())
-            file.delete ();
-
-          /* Make sure to clear EmacsApplication.dumpFileName, or
-             starting Emacs without restarting this program will
-             make Emacs try to load a nonexistent dump file.  */
-          EmacsApplication.dumpFileName = null;
+          eraseDumpFile ();
+          return true;
         }
-      });
-    layout.addView (textView);
+      };
 
-    super.onCreate (savedInstanceState);
+    tem.setOnPreferenceClickListener (listener);
   }
 };
diff --git a/java/org/gnu/emacs/EmacsView.java b/java/org/gnu/emacs/EmacsView.java
index 0416301101c..4fc8104e31f 100644
--- a/java/org/gnu/emacs/EmacsView.java
+++ b/java/org/gnu/emacs/EmacsView.java
@@ -181,7 +181,10 @@ public class EmacsView extends ViewGroup
     if (oldBitmap != null)
       {
         oldBitmap.recycle ();
-        surfaceView.setBitmap (null, null);
+
+        /* Make sure to set the view's bitmap to the new bitmap, or
+           ugly flicker can result.  */
+        surfaceView.setBitmap (bitmap, null);
       }
 
     /* Some Android versions still don't free the bitmap until the
diff --git a/java/res/xml/preferences.xml b/java/res/xml/preferences.xml
new file mode 100644
index 00000000000..f0c3abb52e7
--- /dev/null
+++ b/java/res/xml/preferences.xml
@@ -0,0 +1,28 @@
+<!-- Descriptions for the preferences screen for GNU Emacs on Android.
+
+Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
+
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+    <Preference android:key="start_quick"
+                android:title="Restart Emacs with -Q"
+                android:summary="Restart Emacs, but do not load site lisp or init files."/>
+
+    <Preference android:key="erase_dump"
+                android:title="Delete dump file"
+                android:summary="Remove the dumped state created when Emacs was installed"/>
+</PreferenceScreen>