LoadDb and SaveDb respect the SyncInBackground preference

src/Kp2aBusinessLogic/IKp2aApp.cs

@@ -141,5 +141,8 @@ namespace keepass2android
 
 #endif
 
+		bool SyncInBackgroundPreference { get; set; }
+
+
     }
 }

src/Kp2aBusinessLogic/Io/CachingFileStorage.cs

@@ -186,8 +186,11 @@ namespace keepass2android.Io
                 Kp2aLog.Log("couldn't open from remote " + ioc.Path);
 #endif
 				Kp2aLog.Log(ex.ToString());
-
+                if (TriggerWarningWhenFallingBackToCache)
+                {
                     _cacheSupervisor.CouldntOpenFromRemote(ioc, ex);
+                }
+				
 				return File.OpenRead(cachedFilePath);
 			}
 		}
@@ -327,7 +330,10 @@ namespace keepass2android.Io
 				Kp2aLog.Log("couldn't save to remote " + ioc.Path);
 				Kp2aLog.Log(e.ToString());
 				//notify the supervisor so it might display a warning or schedule a retry
-				_cacheSupervisor.CouldntSaveToRemote(ioc, e);
+                if (TriggerWarningWhenFallingBackToCache)
+                {
+                    _cacheSupervisor.CouldntSaveToRemote(ioc, e); }
+				
 				return false;
 			}
 		}
@@ -632,6 +638,8 @@ namespace keepass2android.Io
 			set { _cachedStorage.IsOffline = value; }
 		}
 
+        public bool TriggerWarningWhenFallingBackToCache { get; set; }
+
         public void OnRequestPermissionsResult(IFileStorageSetupActivity fileStorageSetupActivity, int requestCode,
 			string[] permissions, Permission[] grantResults)
 		{

src/Kp2aBusinessLogic/Io/OfflineSwitchableFileStorage.cs

@@ -11,6 +11,7 @@ namespace keepass2android.Io
 	public interface IOfflineSwitchable
 	{
 		bool IsOffline { get; set; }
+        bool TriggerWarningWhenFallingBackToCache { get; set; }
     }
 
 /// <summary>
@@ -21,6 +22,7 @@ namespace keepass2android.Io
 	{
 		private readonly IFileStorage _baseStorage;
 		public bool IsOffline { get; set; }
+        public bool TriggerWarningWhenFallingBackToCache { get; set; }
 
         public OfflineSwitchableFileStorage(IFileStorage baseStorage)
 		{

src/Kp2aBusinessLogic/database/Database.cs

@@ -194,9 +194,9 @@ namespace keepass2android
 		}
 
 
-		public void SaveData()  {
+		public void SaveData(IFileStorage fileStorage)  {
             
-			using (IWriteTransaction trans = _app.GetFileStorage(Ioc).OpenWriteTransaction(Ioc, _app.GetBooleanPreference(PreferenceKey.UseFileTransactions)))
+			using (IWriteTransaction trans = fileStorage.OpenWriteTransaction(Ioc, _app.GetBooleanPreference(PreferenceKey.UseFileTransactions)))
 			{
 				DatabaseFormat.Save(KpDatabase, trans.OpenFile());
 				

src/Kp2aBusinessLogic/database/edit/LoadDB.cs

@@ -21,8 +21,10 @@ using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Android.App;
+using Android.OS;
 using KeePass.Util;
 using keepass2android.database.edit;
+using keepass2android.Io;
 using KeePassLib;
 using KeePassLib.Keys;
 using KeePassLib.Serialization;
@@ -47,8 +49,6 @@ namespace keepass2android
 			_keyfileOrProvider = keyfileOrProvider;
 		    _updateLastUsageTimestamp = updateLastUsageTimestamp;
 		    _makeCurrent = makeCurrent;
-
-
 		    _rememberKeyfile = app.GetBooleanPreference(PreferenceKey.remember_keyfile); 
 		}
 
@@ -65,16 +65,31 @@ namespace keepass2android
                     //make sure the file data is stored in the recent files list even if loading fails
 				    SaveFileData(_ioc, _keyfileOrProvider);
 
+                    var fileStorage = _app.GetFileStorage(_ioc);
+
+                    bool requiresSubsequentSync = false;
+
 
                     StatusLogger.UpdateMessage(UiStringKey.loading_database);
 					//get the stream data into a single stream variable (databaseStream) regardless whether its preloaded or not:
 					MemoryStream preloadedMemoryStream = _databaseData == null ? null : _databaseData.Result;
 					MemoryStream databaseStream;
                     if (preloadedMemoryStream != null)
+                    {
+						//note: if the stream has been loaded already, we don't need to trigger another sync later on
                         databaseStream = preloadedMemoryStream;
+                    }
                     else
 					{
-						using (Stream s = _app.GetFileStorage(_ioc).OpenFileForRead(_ioc))
+                        if (_app.SyncInBackgroundPreference && fileStorage is IOfflineSwitchable offlineSwitchable)
+                        {
+                            offlineSwitchable.IsOffline = true;
+							//no warning. We'll trigger a sync later.
+                            offlineSwitchable.TriggerWarningWhenFallingBackToCache = false;
+                            requiresSubsequentSync = true;
+
+                        }
+                        using (Stream s = fileStorage.OpenFileForRead(_ioc))
 						{
 							databaseStream = new MemoryStream();
 							s.CopyTo(databaseStream);
@@ -83,8 +98,8 @@ namespace keepass2android
 					}
 
 					//ok, try to load the database. Let's start with Kdbx format and retry later if that is the wrong guess:
-					_format = new KdbxDatabaseFormat(KdbxDatabaseFormat.GetFormatToUse(_app.GetFileStorage(_ioc).GetFileExtension(_ioc)));
+					_format = new KdbxDatabaseFormat(KdbxDatabaseFormat.GetFormatToUse(fileStorage.GetFileExtension(_ioc)));
-					TryLoad(databaseStream);
+					TryLoad(databaseStream, requiresSubsequentSync);
 
 
 
@@ -136,7 +151,7 @@ namespace keepass2android
 		/// </summary>
 		public Exception Exception { get; set; }
 
-		Database TryLoad(MemoryStream databaseStream)
+		Database TryLoad(MemoryStream databaseStream, bool requiresSubsequentSync)
 		{
 			//create a copy of the stream so we can try again if we get an exception which indicates we should change parameters
 			//This is not optimal in terms of (short-time) memory usage but is hard to avoid because the Keepass library closes streams also in case of errors.
@@ -152,13 +167,26 @@ namespace keepass2android
                 Database newDb = _app.LoadDatabase(_ioc, workingCopy, _compositeKey, StatusLogger, _format, _makeCurrent);
                 Kp2aLog.Log("LoadDB OK");
                 
+                if (requiresSubsequentSync)
+                {
+                    var syncTask = new SynchronizeCachedDatabase(ActiveActivity, _app, new ActionOnOperationFinished(ActiveActivity,
+                        (success, message, activeActivity) =>
+                        {
+                            if (!String.IsNullOrEmpty(message))
+                                _app.ShowMessage(activeActivity, message, success ? MessageSeverity.Info : MessageSeverity.Error);
+                          
+                        })  
+                    );
+                    BackgroundOperationRunner.Instance.Run(ActiveActivity, _app, syncTask);
+                }
+
                 Finish(true, _format.SuccessMessage);
 			    return newDb;
 			}
 			catch (OldFormatException)
 			{
 				_format = new KdbDatabaseFormat(_app);
-				return TryLoad(databaseStream);
+				return TryLoad(databaseStream, requiresSubsequentSync);
 			}
 			catch (InvalidCompositeKeyException)
 			{
@@ -170,7 +198,7 @@ namespace keepass2android
 					//retry without password:
 					_compositeKey.RemoveUserKey(passwordKey);
 					//retry:
-					return TryLoad(databaseStream);
+					return TryLoad(databaseStream, requiresSubsequentSync);
 				}
 				else throw;
 			}

src/Kp2aBusinessLogic/database/edit/SaveDB.cs

@@ -38,6 +38,7 @@ namespace keepass2android
 		private readonly IKp2aApp _app;
 	    private readonly Database _db;
 	    private readonly bool _dontSave;
+		private bool requiresSubsequentSync = false; //if true, we need to sync the file after saving.
 
         /// <summary>
 		/// stream for reading the data from the original file. If this is set to a non-null value, we know we need to sync
@@ -108,13 +109,23 @@ namespace keepass2android
 					IOConnectionInfo ioc = _db.Ioc;
 					IFileStorage fileStorage = _app.GetFileStorage(ioc);
 
+                    if (_app.SyncInBackgroundPreference && fileStorage is IOfflineSwitchable offlineSwitchable)
+                    {
+                        offlineSwitchable.IsOffline = true;
+                        //no warning. We'll trigger a sync later.
+                        offlineSwitchable.TriggerWarningWhenFallingBackToCache = false;
+                        requiresSubsequentSync = true;
+
+                    }
+
+
                     if (_streamForOrigFile == null)
 					{
 						if ((!_app.GetBooleanPreference(PreferenceKey.CheckForFileChangesOnSave))
 							|| (_db.KpDatabase.HashOfFileOnDisk == null)) //first time saving
 						{
 							PerformSaveWithoutCheck(fileStorage, ioc);
-							Finish(true);
+							FinishWithSuccess();
 							return;
 						}	
 					}
@@ -123,9 +134,9 @@ namespace keepass2android
                     bool hasStreamForOrigFile = (_streamForOrigFile != null);
                     bool hasChangeFast = hasStreamForOrigFile ||
                                          fileStorage.CheckForFileChangeFast(ioc, _db.LastFileVersion);  //first try to use the fast change detection;
-                    bool hasHashChanged = hasChangeFast ||
+                    bool hasHashChanged = !requiresSubsequentSync && (hasChangeFast ||
                                           (FileHashChanged(ioc, _db.KpDatabase.HashOfFileOnDisk) ==
-                                           FileHashChange.Changed); //if that fails, hash the file and compare:
+                                           FileHashChange.Changed)); //if that fails, hash the file and compare:
 
 					if (hasHashChanged)
 					{
@@ -158,7 +169,7 @@ namespace keepass2android
 								RunInWorkerThread(() =>
 									{
 										PerformSaveWithoutCheck(fileStorage, ioc);
-										Finish(true);
+										FinishWithSuccess();
 									});
 							},
 							//cancel 
@@ -174,7 +185,7 @@ namespace keepass2android
 					else
 					{
 						PerformSaveWithoutCheck(fileStorage, ioc);
-						Finish(true);
+						FinishWithSuccess();
 					}
 
 				}
@@ -194,11 +205,28 @@ namespace keepass2android
 			}
 			else
 			{
-				Finish(true);
+				FinishWithSuccess();
 			}
 			
 		}
 
+        private void FinishWithSuccess()
+        {
+            if (requiresSubsequentSync)
+            {
+                var syncTask = new SynchronizeCachedDatabase(ActiveActivity, _app, new ActionOnOperationFinished(ActiveActivity,
+                    (success, message, activeActivity) =>
+                    {
+                        if (!System.String.IsNullOrEmpty(message))
+                            _app.ShowMessage(activeActivity, message, success ? MessageSeverity.Info : MessageSeverity.Error);
+
+                    })
+                );
+                BackgroundOperationRunner.Instance.Run(ActiveActivity, _app, syncTask);
+            }
+            Finish(true);
+        }
+
         private void MergeAndFinish(IFileStorage fileStorage, IOConnectionInfo ioc)
         {
             //note: when synced, the file might be downloaded once again from the server. Caching the data
@@ -207,7 +235,7 @@ namespace keepass2android
             MergeIn(fileStorage, ioc);
             PerformSaveWithoutCheck(fileStorage, ioc);
             _db.UpdateGlobals();
-            Finish(true);
+            FinishWithSuccess();
         }
 
         private void RunInWorkerThread(Action runHandler)
@@ -282,7 +310,7 @@ namespace keepass2android
 		private void PerformSaveWithoutCheck(IFileStorage fileStorage, IOConnectionInfo ioc)
 		{
 			StatusLogger.UpdateSubMessage("");
-			_db.SaveData();
+			_db.SaveData(fileStorage);
 			_db.LastFileVersion = fileStorage.GetCurrentFileVersionFast(ioc);
 		}
 

src/keepass2android-app/PasswordActivity.cs

@@ -1753,17 +1753,10 @@ namespace keepass2android
                 cbOfflineMode.Checked =
                     App.Kp2a
                         .OfflineModePreference; //this won't overwrite new user settings because every change is directly saved in settings
-            LinearLayout offlineModeContainer = FindViewById<LinearLayout>(Resource.Id.work_offline_container);
+
-            var cachingFileStorage = App.Kp2a.GetFileStorage(_ioConnection) as CachingFileStorage;
+            CheckBox cbSyncInBackground = (CheckBox)FindViewById(Resource.Id.sync_in_background)!;
-            if ((cachingFileStorage != null) && cachingFileStorage.IsCached(_ioConnection))
+            cbSyncInBackground.Checked = App.Kp2a.SyncInBackgroundPreference;
-            {
+            UpdateInternalCacheCheckboxesVisibility();
-                offlineModeContainer.Visibility = ViewStates.Visible;
-            }
-            else
-            {
-                offlineModeContainer.Visibility = ViewStates.Gone;
-                App.Kp2a.OfflineMode = false;
-            }
 
 
 
@@ -2040,6 +2033,34 @@ namespace keepass2android
 				App.Kp2a.OfflineModePreference = App.Kp2a.OfflineMode = args.IsChecked;
 			};
 
+            CheckBox cbSyncInBackground = (CheckBox)FindViewById(Resource.Id.sync_in_background);
+            cbSyncInBackground.CheckedChange += (sender, args) =>
+            {
+                App.Kp2a.SyncInBackgroundPreference = args.IsChecked;
+                UpdateInternalCacheCheckboxesVisibility();
+
+            };
+
+        }
+
+        private void UpdateInternalCacheCheckboxesVisibility()
+        {
+
+            LinearLayout syncInBackgroundContainer = FindViewById<LinearLayout>(Resource.Id.sync_in_background_container)!;
+
+            LinearLayout offlineModeContainer = FindViewById<LinearLayout>(Resource.Id.work_offline_container)!;
+            var cachingFileStorage = App.Kp2a.GetFileStorage(_ioConnection) as CachingFileStorage;
+            if ((cachingFileStorage != null) && cachingFileStorage.IsCached(_ioConnection))
+            {
+                syncInBackgroundContainer.Visibility = ViewStates.Visible;
+                offlineModeContainer.Visibility =
+                    App.Kp2a.SyncInBackgroundPreference ? ViewStates.Gone : ViewStates.Visible;
+            }
+            else
+            {
+                syncInBackgroundContainer.Visibility = offlineModeContainer.Visibility = ViewStates.Gone;
+                App.Kp2a.OfflineMode = false;
+            }
         }
 
         private String LoadKeyProviderStringForIoc(String filename) {

src/keepass2android-app/Resources/layout/password.xml

@@ -318,6 +318,30 @@
 			          android:text="@string/help_quickunlock"
                       />
                   </LinearLayout>
+
+                    
+                    <LinearLayout
+                      android:id="@+id/sync_in_background_container"
+                      android:orientation="horizontal"
+                      android:layout_width="fill_parent"
+                      android:layout_height="wrap_content">
+
+                      <CheckBox
+                        android:id="@+id/sync_in_background"
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        android:layout_marginTop="16dp"
+                        android:text="@string/SyncOfflineCacheInBackground_title" />
+                      <keepass2android.views.Kp2aShortHelpView
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        style="@style/TextAppearance_Help_Dense"
+                      
+                        app:help_text="@string/SyncOfflineCacheInBackground_summary"
+                        app:title_text="@string/SyncOfflineCacheInBackground_title"
+                        android:text="@string/SyncOfflineCacheInBackground_summary"
+                      />
+                    </LinearLayout>
                   <LinearLayout
                     android:id="@+id/work_offline_container"
                     android:orientation="horizontal"
@@ -328,7 +352,7 @@
                           android:id="@+id/work_offline"
                           android:layout_width="wrap_content"
                           android:layout_height="wrap_content"
-                          android:layout_marginTop="16dp"
+                          
                           android:text="@string/UseOfflineMode" />
                     <keepass2android.views.Kp2aShortHelpView
                       android:layout_width="wrap_content"
@@ -341,6 +365,7 @@
                       />
                   </LinearLayout>
 
+
                   <Button
                         android:id="@+id/kill_app"
                         android:text="@string/kill_app_label"

src/keepass2android-app/SyncUtil.cs

@@ -55,13 +55,17 @@ namespace keepass2android
             var filestorage = App.Kp2a.GetFileStorage(App.Kp2a.CurrentDb.Ioc);
             OperationWithFinishHandler task;
             OnOperationFinishedHandler onOperationFinishedHandler = new ActionOnOperationFinished(_activity, (success, message, activity) =>
+            {
+                new Handler(Looper.MainLooper).Post(() =>
                 {
                     if (!String.IsNullOrEmpty(message))
                         App.Kp2a.ShowMessage(activity, message, success ? MessageSeverity.Info : MessageSeverity.Error);
 
                     // Tell the adapter to refresh it's list
                     BaseAdapter adapter = (activity as GroupBaseActivity)?.ListAdapter;
-                new Handler(Looper.MainLooper).Post(() => adapter?.NotifyDataSetChanged());
+
+                    adapter?.NotifyDataSetChanged();
+                });
 
                 if (App.Kp2a.CurrentDb?.OtpAuxFileIoc != null)
                 {

src/keepass2android-app/Utils/MessagePresenter.cs

@@ -45,8 +45,11 @@ namespace keepass2android.Utils
     internal class ToastPresenter : IMessagePresenter
     {
         public void ShowMessage(Message message)
+        {
+            new Handler(Looper.MainLooper).Post(() =>
             {
                 Toast.MakeText(App.Context, message.Text, ToastLength.Long).Show();
+            });
         }
 
         public List<Message> PendingMessages => new();

src/keepass2android-app/app/App.cs

@@ -798,9 +798,14 @@ namespace keepass2android
 					fileStorage = innerFileStorage;
 				}
 			}
-			if (fileStorage is IOfflineSwitchable)
+			if (fileStorage is IOfflineSwitchable switchable)
 			{
-				((IOfflineSwitchable)fileStorage).IsOffline = App.Kp2a.OfflineMode;
+				switchable.IsOffline = App.Kp2a.OfflineMode;
+                if (switchable.IsOffline)
+                {
+					//users of the file storage can set this to false, but the default is to show a warning:
+                    switchable.TriggerWarningWhenFallingBackToCache = true;
+                }
 			}
 			return fileStorage;
 		}
@@ -1151,6 +1156,24 @@ namespace keepass2android
 			}
 		}
 
+
+        public bool SyncInBackgroundPreference
+        {
+            get
+            {
+                var prefs = PreferenceManager.GetDefaultSharedPreferences(LocaleManager.LocalizedAppContext);
+                return prefs.GetBoolean(LocaleManager.LocalizedAppContext.GetString(Resource.String.SyncOfflineCacheInBackground_key), false);
+            }
+            set
+            {
+                ISharedPreferences prefs = PreferenceManager.GetDefaultSharedPreferences(LocaleManager.LocalizedAppContext);
+                ISharedPreferencesEditor edit = prefs.Edit();
+                edit.PutBoolean(LocaleManager.LocalizedAppContext.GetString(Resource.String.SyncOfflineCacheInBackground_key), value);
+                edit.Commit();
+
+            }
+        }
+
         /// <summary>
         /// true if the app is used in offline mode
         /// </summary>