Fix camera capture crash on devices with lower RAM

app/android/src/uk/co/lutraconsulting/CameraActivity.java

@@ -78,6 +78,7 @@ protected void onCreate(Bundle savedInstanceState) {
 
                 takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);
                 takePictureIntent.putExtra("__RESULT__", "takePictureIntent__RESULT__");
+                startForegroundService(new Intent(this, CameraForegroundService.class));
                 startActivityForResult(takePictureIntent, CAMERA_CODE);
             } else {
                 Intent activityIntent = getIntent();
@@ -115,6 +116,11 @@ protected void onActivityResult(int requestCode, int resultCode, Intent data) {
         Log.d(TAG, "resultCode: " + resultCode);
         orientationSensor.Unregister();
 
+        if (requestCode == CAMERA_CODE) {
+            // no-op if it isn't running (e.g. process was killed and recreated), stops it either way
+            stopService(new Intent(this, CameraForegroundService.class));
+        }
+
         if (requestCode == CAMERA_CODE && resultCode == Activity.RESULT_OK) {
             Log.d(TAG, "tmp exists: " + cameraFile.exists());
             Log.d(TAG, "tmp path: " + cameraFile.getAbsolutePath());
@@ -142,6 +148,13 @@ protected void onActivityResult(int requestCode, int resultCode, Intent data) {
         finish();
     }
 
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        // no-op if it was already stopped in onActivityResult() or never started
+        stopService(new Intent(this, CameraForegroundService.class));
+    }
+
     private void extendGPSExifData(long captureTime) {
         int direction = getValueByTime(orientationSensor.m_azimuth_data, captureTime);
         if (direction < 0) {

app/android/src/uk/co/lutraconsulting/CameraForegroundService.java

@@ -0,0 +1,77 @@
+/***************************************************************************
+ *                                                                         *
+ *   This program 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 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+package uk.co.lutraconsulting;
+
+import android.os.Build;
+import android.os.IBinder;
+import android.app.Service;
+import android.app.PendingIntent;
+import android.content.Intent;
+import android.content.pm.ServiceInfo;
+
+import android.app.Notification;
+import android.app.NotificationChannel;
+import android.app.NotificationManager;
+
+/**
+ * Runs in the app's default process for as long as CameraActivity is waiting on the external
+ * camera app, to raise this process's priority and make it much less likely to be killed while
+ * the camera is in the foreground.
+ * This is a mitigation, not a guarantee -- under severe enough memory pressure the process can
+ * still be killed; CameraActivity does not currently resume state after that, so a kill mid-wait
+ * causes the camera capture to restart from scratch on the recreated process.
+ */
+public class CameraForegroundService extends Service {
+
+    private static final String CHANNEL_ID = "CameraForegroundServiceChannel";
+    private static final int SERVICE_ID = 1011;
+
+    @Override
+    public IBinder onBind(Intent intent) {
+        return null;
+    }
+
+    @Override
+    public int onStartCommand(Intent intent, int flags, int startId) {
+        NotificationChannel serviceChannel = new NotificationChannel(
+                CHANNEL_ID,
+                "Camera Foreground Service Channel",
+                NotificationManager.IMPORTANCE_LOW
+        );
+
+        NotificationManager manager = getSystemService(NotificationManager.class);
+        manager.createNotificationChannel(serviceChannel);
+
+        Intent notificationIntent = new Intent(this, MMActivity.class);
+        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, PendingIntent.FLAG_IMMUTABLE);
+
+        Notification notification = new Notification.Builder(this, CHANNEL_ID)
+                .setSmallIcon(R.drawable.ic_notification)
+                .setContentTitle("Waiting for photo")
+                .setColor(getResources().getColor(R.color.grassColor))
+                .setContentIntent(pendingIntent)
+                .build();
+
+        // We never request the POST_NOTIFICATIONS runtime permission from the user, so this
+        // notification will silently not be shown unless the user has manually enabled it for
+        // the app in system Settings. startForeground() still succeeds and still elevates the
+        // process's priority either way -- the permission only gates the notification's
+        // visibility, not the foreground service state itself.
+        if (Build.VERSION.SDK_INT >= 35) {
+            startForeground(SERVICE_ID, notification, ServiceInfo.FOREGROUND_SERVICE_TYPE_SHORT_SERVICE);
+        } else {
+            startForeground(SERVICE_ID, notification);
+        }
+
+        // if this service alone gets killed there is nothing useful to resume, it only exists to
+        // keep the process's priority elevated while CameraActivity waits on startActivityForResult().
+        return START_NOT_STICKY;
+    }
+}

cmake_templates/AndroidManifest.xml.in

@@ -104,6 +104,13 @@
             android:stopWithTask="true"
             android:exported="false"
             />
+
+        <service
+            android:name=".CameraForegroundService"
+            android:foregroundServiceType="shortService"
+            android:stopWithTask="true"
+            android:exported="false"
+            />
     </application>
 
     <!-- Explicitly mention that we need to use external app for capturing an image and open file-->