[android] Save and restore list position of conversation across restarts

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

@@ -8,6 +8,7 @@ import android.content.DialogInterface;
 import android.content.Intent;
 import android.net.Uri;
 import android.os.Bundle;
+import android.os.Parcelable;
 import android.support.annotation.Nullable;
 import android.support.annotation.UiThread;
 import android.support.design.widget.Snackbar;
@@ -107,7 +108,6 @@ import static android.support.v4.app.ActivityOptionsCompat.makeSceneTransitionAn
 import static android.support.v4.view.ViewCompat.setTransitionName;
 import static android.support.v7.util.SortedList.INVALID_POSITION;
 import static android.view.Gravity.RIGHT;
-import static android.widget.Toast.LENGTH_LONG;
 import static android.widget.Toast.LENGTH_SHORT;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.sort;
@@ -121,9 +121,9 @@ import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 import static org.briarproject.briar.android.TestingConstants.FEATURE_FLAG_IMAGE_ATTACHMENTS;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_ATTACH_IMAGE;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_INTRODUCTION;
+import static org.briarproject.briar.android.conversation.ImageActivity.ATTACHMENTS;
 import static org.briarproject.briar.android.conversation.ImageActivity.ATTACHMENT_POSITION;
 import static org.briarproject.briar.android.conversation.ImageActivity.DATE;
-import static org.briarproject.briar.android.conversation.ImageActivity.ATTACHMENTS;
 import static org.briarproject.briar.android.conversation.ImageActivity.NAME;
 import static org.briarproject.briar.android.settings.SettingsFragment.SETTINGS_NAMESPACE;
 import static org.briarproject.briar.android.util.UiUtils.getAvatarTransitionName;
@@ -194,6 +194,8 @@ public class ConversationActivity extends BriarActivity
 	ViewModelProvider.Factory viewModelFactory;
 
 	private volatile ContactId contactId;
+	@Nullable
+	private Parcelable layoutManagerState;
 
 	private final Observer<String> contactNameObserver = name -> {
 		requireNonNull(name);
@@ -309,6 +311,21 @@ public class ConversationActivity extends BriarActivity
 		list.stopPeriodicUpdate();
 	}
 
+	@Override
+	protected void onSaveInstanceState(Bundle outState) {
+		super.onSaveInstanceState(outState);
+		if (layoutManager != null) {
+			layoutManagerState = layoutManager.onSaveInstanceState();
+			outState.putParcelable("layoutManager", layoutManagerState);
+		}
+	}
+
+	@Override
+	protected void onRestoreInstanceState(Bundle savedInstanceState) {
+		super.onRestoreInstanceState(savedInstanceState);
+		layoutManagerState = savedInstanceState.getParcelable("layoutManager");
+	}
+
 	@Override
 	public boolean onCreateOptionsMenu(Menu menu) {
 		// Inflate the menu items for use in the action bar
@@ -428,8 +445,12 @@ public class ConversationActivity extends BriarActivity
 				List<ConversationItem> items = createItems(headers);
 				adapter.addAll(items);
 				list.showData();
-				// Scroll to the bottom
+				if (layoutManagerState == null) {
-				list.scrollToPosition(adapter.getItemCount() - 1);
+					// Scroll to the bottom
+					list.scrollToPosition(adapter.getItemCount() - 1);
+				} else {
+					layoutManager.onRestoreInstanceState(layoutManagerState);
+				}
 			} else {
 				LOG.info("Concurrent update, reloading");
 				loadMessages();
@@ -471,7 +492,8 @@ public class ConversationActivity extends BriarActivity
 					adapter.getMessageItem(m);
 			if (pair != null) {
 				pair.getSecond().setText(text);
-				boolean bottom = adapter.isScrolledToBottom(layoutManager);
+				boolean bottom = layoutManagerState == null &&
+						adapter.isScrolledToBottom(layoutManager);
 				adapter.notifyItemChanged(pair.getFirst());
 				if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
 			}
@@ -502,7 +524,8 @@ public class ConversationActivity extends BriarActivity
 					adapter.getMessageItem(m);
 			if (pair != null) {
 				pair.getSecond().setAttachments(items);
-				boolean bottom = adapter.isScrolledToBottom(layoutManager);
+				boolean bottom = layoutManagerState == null &&
+						adapter.isScrolledToBottom(layoutManager);
 				adapter.notifyItemChanged(pair.getFirst());
 				if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
 			}
@@ -553,7 +576,8 @@ public class ConversationActivity extends BriarActivity
 
 	private void addConversationItem(ConversationItem item) {
 		runOnUiThreadUnlessDestroyed(() -> {
-			boolean bottom = adapter.isScrolledToBottom(layoutManager);
+			boolean bottom = layoutManagerState == null &&
+					adapter.isScrolledToBottom(layoutManager);
 			adapter.incrementRevision();
 			adapter.add(item);
 			if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);

briar-android/src/main/res/layout/activity_conversation.xml

@@ -49,7 +49,8 @@
 		android:id="@+id/conversationView"
 		android:layout_width="match_parent"
 		android:layout_height="0dp"
-		android:layout_weight="2"/>
+		android:layout_weight="2"
+		app:scrollToEnd="false"/>
 
 	<org.briarproject.briar.android.view.ImagePreview
 		android:id="@+id/imagePreview"