Add methods to DbViewModel for loading and updating lists of items

briar-android/src/main/java/org/briarproject/briar/android/contact/add/remote/AddContactViewModel.java

@@ -9,6 +9,7 @@ import org.briarproject.bramble.api.contact.PendingContact;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.NoSuchPendingContactException;
+import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.briar.android.viewmodel.DbViewModel;
@@ -52,8 +53,9 @@ public class AddContactViewModel extends DbViewModel {
 	AddContactViewModel(Application application,
 			ContactManager contactManager,
 			@DatabaseExecutor Executor dbExecutor,
-			LifecycleManager lifecycleManager) {
+			LifecycleManager lifecycleManager,
-		super(application, dbExecutor, lifecycleManager);
+			TransactionManager db) {
+		super(application, dbExecutor, lifecycleManager, db);
 		this.contactManager = contactManager;
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/contact/add/remote/PendingContactListViewModel.java

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.contact.event.PendingContactRemovedEvent;
 import org.briarproject.bramble.api.contact.event.PendingContactStateChangedEvent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -56,10 +57,11 @@ public class PendingContactListViewModel extends DbViewModel
 	PendingContactListViewModel(Application application,
 			@DatabaseExecutor Executor dbExecutor,
 			LifecycleManager lifecycleManager,
+			TransactionManager db,
 			ContactManager contactManager,
 			RendezvousPoller rendezvousPoller,
 			EventBus eventBus) {
-		super(application, dbExecutor, lifecycleManager);
+		super(application, dbExecutor, lifecycleManager, db);
 		this.contactManager = contactManager;
 		this.rendezvousPoller = rendezvousPoller;
 		this.eventBus = eventBus;

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationViewModel.java

@@ -113,7 +113,7 @@ public class ConversationViewModel extends DbViewModel
 			PrivateMessageFactory privateMessageFactory,
 			AttachmentRetriever attachmentRetriever,
 			AttachmentCreator attachmentCreator) {
-		super(application, dbExecutor, lifecycleManager);
+		super(application, dbExecutor, lifecycleManager, db);
 		this.db = db;
 		this.eventBus = eventBus;
 		this.messagingManager = messagingManager;

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageViewModel.java

@@ -7,6 +7,7 @@ import android.view.View;
 
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -78,8 +79,9 @@ public class ImageViewModel extends DbViewModel implements EventListener {
 			EventBus eventBus,
 			@DatabaseExecutor Executor dbExecutor,
 			LifecycleManager lifecycleManager,
+			TransactionManager db,
 			@IoExecutor Executor ioExecutor) {
-		super(application, dbExecutor, lifecycleManager);
+		super(application, dbExecutor, lifecycleManager, db);
 		this.messagingManager = messagingManager;
 		this.eventBus = eventBus;
 		this.ioExecutor = ioExecutor;

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/NavDrawerViewModel.java

@@ -4,6 +4,7 @@ import android.app.Application;
 
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.settings.Settings;
@@ -51,8 +52,9 @@ public class NavDrawerViewModel extends DbViewModel {
 	NavDrawerViewModel(Application app,
 			@DatabaseExecutor Executor dbExecutor,
 			LifecycleManager lifecycleManager,
+			TransactionManager db,
 			SettingsManager settingsManager) {
-		super(app, dbExecutor, lifecycleManager);
+		super(app, dbExecutor, lifecycleManager, db);
 		this.settingsManager = settingsManager;
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/PluginViewModel.java

@@ -9,6 +9,7 @@ import android.content.IntentFilter;
 
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -85,10 +86,10 @@ public class PluginViewModel extends DbViewModel implements EventListener {
 
 	@Inject
 	PluginViewModel(Application app, @DatabaseExecutor Executor dbExecutor,
-			LifecycleManager lifecycleManager,
+			LifecycleManager lifecycleManager, TransactionManager db,
 			SettingsManager settingsManager, PluginManager pluginManager,
 			EventBus eventBus, NetworkManager networkManager) {
-		super(app, dbExecutor, lifecycleManager);
+		super(app, dbExecutor, lifecycleManager, db);
 		this.app = app;
 		this.settingsManager = settingsManager;
 		this.pluginManager = pluginManager;

briar-android/src/main/java/org/briarproject/briar/android/viewmodel/DbViewModel.java

@@ -1,20 +1,36 @@
 package org.briarproject.briar.android.viewmodel;
 
 import android.app.Application;
+import android.os.Handler;
 
 import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbCallable;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.ListIterator;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
 import javax.annotation.concurrent.Immutable;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.UiThread;
+import androidx.arch.core.util.Function;
 import androidx.lifecycle.AndroidViewModel;
+import androidx.lifecycle.LiveData;
+import androidx.recyclerview.widget.RecyclerView;
 
+import static android.os.Looper.getMainLooper;
+import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.LogUtils.logException;
 
 @Immutable
 @NotNullByDefault
@@ -25,17 +41,28 @@ public abstract class DbViewModel extends AndroidViewModel {
 	@DatabaseExecutor
 	private final Executor dbExecutor;
 	private final LifecycleManager lifecycleManager;
+	private final TransactionManager db;
 
 	public DbViewModel(
 			@NonNull Application application,
 			@DatabaseExecutor Executor dbExecutor,
-			LifecycleManager lifecycleManager) {
+			LifecycleManager lifecycleManager,
+			TransactionManager db) {
 		super(application);
 		this.dbExecutor = dbExecutor;
 		this.lifecycleManager = lifecycleManager;
+		this.db = db;
 	}
 
-	public void runOnDbThread(Runnable task) {
+	/**
+	 * Runs the given task on the {@link DatabaseExecutor}
+	 * and waits for the DB to open.
+	 * <p>
+	 * If you need a list of items to be displayed in a
+	 * {@link RecyclerView.Adapter},
+	 * use {@link #loadList(DbCallable, UiCallable)} instead.
+	 */
+	protected void runOnDbThread(Runnable task) {
 		dbExecutor.execute(() -> {
 			try {
 				lifecycleManager.waitForDatabase();
@@ -47,4 +74,119 @@ public abstract class DbViewModel extends AndroidViewModel {
 		});
 	}
 
+	/**
+	 * Loads a list of items on the {@link DatabaseExecutor} within a single
+	 * {@link Transaction} and publishes it as a {@link LiveResult}
+	 * to the {@link UiThread}.
+	 * <p>
+	 * Use this to ensure that modifications to your local list do not get
+	 * overridden by database loads that were in progress while the modification
+	 * was made.
+	 * E.g. An event about the removal of a message causes the message item to
+	 * be removed from the local list while all messages are reloaded.
+	 * This method ensures that those operations can be processed on the
+	 * UiThread in the correct order so that the removed message will not be
+	 * re-added when the re-load completes.
+	 */
+	protected <T extends List<?>> void loadList(
+			DbCallable<T, DbException> task,
+			UiCallable<LiveResult<T>> uiUpdate) {
+		dbExecutor.execute(() -> {
+			try {
+				lifecycleManager.waitForDatabase();
+				db.transaction(true, txn -> {
+					T t = task.call(txn);
+					txn.attach(() -> uiUpdate.call(new LiveResult<>(t)));
+				});
+			} catch (InterruptedException e) {
+				LOG.warning("Interrupted while waiting for database");
+				Thread.currentThread().interrupt();
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				new Handler(getMainLooper())
+						.post(() -> uiUpdate.call(new LiveResult<>(e)));
+			}
+		});
+	}
+
+	@NotNullByDefault
+	public interface UiCallable<T> {
+		@UiThread
+		void call(T t);
+	}
+
+	/**
+	 * Creates a copy of the list available in the given LiveData
+	 * and replaces items where the given test function returns true.
+	 *
+	 * @return a copy of the list in the LiveData with item(s) replaced
+	 * or null when the
+	 * <ul>
+	 * <li> LiveData does not have a value
+	 * <li> LiveResult in the LiveData has an error
+	 * <li> test function did return false for all items in the list
+	 * </ul>
+	 */
+	@Nullable
+	protected <T> List<T> updateListItem(
+			LiveData<LiveResult<List<T>>> liveData, Function<T, Boolean> test,
+			Function<T, T> replacer) {
+		List<T> items = getList(liveData);
+		if (items == null) return null;
+
+		ListIterator<T> iterator = items.listIterator();
+		boolean changed = false;
+		while (iterator.hasNext()) {
+			T item = iterator.next();
+			if (test.apply(item)) {
+				changed = true;
+				iterator.set(replacer.apply(item));
+			}
+		}
+		return changed ? items : null;
+	}
+
+	/**
+	 * Creates a copy of the list available in the given LiveData
+	 * and removes the items from it where the given test function returns true.
+	 *
+	 * @return a copy of the list in the LiveData with item(s) removed
+	 * or null when the
+	 * <ul>
+	 * <li> LiveData does not have a value
+	 * <li> LiveResult in the LiveData has an error
+	 * <li> test function did return false for all items in the list
+	 * </ul>
+	 */
+	@Nullable
+	protected <T> List<T> removeListItem(
+			LiveData<LiveResult<List<T>>> liveData, Function<T, Boolean> test) {
+		List<T> items = getList(liveData);
+		if (items == null) return null;
+
+		ListIterator<T> iterator = items.listIterator();
+		boolean changed = false;
+		while (iterator.hasNext()) {
+			T item = iterator.next();
+			if (test.apply(item)) {
+				changed = true;
+				iterator.remove();
+			}
+		}
+		return changed ? items : null;
+	}
+
+	/**
+	 * Retrieves the list of items from the given LiveData
+	 * or null if it is not available.
+	 */
+	@Nullable
+	private <T> List<T> getList(LiveData<LiveResult<List<T>>> liveData) {
+		LiveResult<List<T>> value = liveData.getValue();
+		if (value == null) return null;
+		List<T> list = value.getResultOrNull();
+		if (list == null) return null;
+		return new ArrayList<>(list);
+	}
+
 }

briar-android/src/main/java/org/briarproject/briar/android/viewmodel/LiveResult.java

@@ -8,9 +8,9 @@ import androidx.annotation.Nullable;
 public class LiveResult<T> {
 
 	@Nullable
-	private T result;
+	private final T result;
 	@Nullable
-	private Exception exception;
+	private final Exception exception;
 
 	public LiveResult(T result) {
 		this.result = result;