Final touches to cloud backup: being future-compatible by not using the agent helpers (those manage the backup state themselves, and we don't want to have to follow their format)

MyTracks/AndroidManifest.xml

@@ -5,7 +5,7 @@
           android:versionName="1.0.16">
   <application android:icon="@drawable/arrow_icon"
                android:label="@string/app_name"
-               android:backupAgent="com.google.android.apps.mytracks.io.backup.MyTracksBackupAgentHelper">
+               android:backupAgent="com.google.android.apps.mytracks.io.backup.MyTracksBackupAgent">
     <uses-library android:name="com.google.android.maps" />
 
     <meta-data android:name="com.google.android.backup.api_key"

MyTracks/src/com/google/android/apps/mytracks/io/backup/MyTracksBackupAgent.java

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.android.apps.mytracks.io.backup;
+
+import com.google.android.apps.mytracks.MyTracksConstants;
+import com.google.android.apps.mytracks.MyTracksSettings;
+
+import android.app.backup.BackupAgent;
+import android.app.backup.BackupDataInput;
+import android.app.backup.BackupDataOutput;
+import android.content.SharedPreferences;
+import android.os.ParcelFileDescriptor;
+import android.util.Log;
+
+import java.io.IOException;
+
+/**
+ * Backup agent used to backup and restore all preferences.
+ * We use a regular {@link BackupAgent} instead of the convenient helpers in
+ * order to be future-proof (assuming we'll want to back up tracks later).
+ * 
+ * @author Rodrigo Damazio
+ */
+public class MyTracksBackupAgent extends BackupAgent {
+  private static final String PREFERENCES_ENTITY = "prefs";
+
+  @Override
+  public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
+      ParcelFileDescriptor newState) throws IOException {
+    Log.i(MyTracksConstants.TAG, "Performing backup");
+    SharedPreferences preferences = this.getSharedPreferences(
+        MyTracksSettings.SETTINGS_NAME, 0);
+
+    backupPreferences(data, preferences);
+    Log.i(MyTracksConstants.TAG, "Backup complete");
+  }
+
+  private void backupPreferences(BackupDataOutput data,
+      SharedPreferences preferences) throws IOException {
+    PreferenceBackupHelper preferenceDumper = createPreferenceBackupHelper();
+    byte[] dumpedContents = preferenceDumper.exportPreferences(preferences);
+    data.writeEntityHeader(PREFERENCES_ENTITY, dumpedContents.length);
+    data.writeEntityData(dumpedContents, dumpedContents.length);
+  }
+
+  protected PreferenceBackupHelper createPreferenceBackupHelper() {
+    return new PreferenceBackupHelper();
+  }
+
+  @Override
+  public void onRestore(BackupDataInput data, int appVersionCode,
+      ParcelFileDescriptor newState) throws IOException {
+    Log.i(MyTracksConstants.TAG, "Restoring from backup");
+    while (data.readNextHeader()) {
+      String key = data.getKey();
+      Log.d(MyTracksConstants.TAG, "Restoring entity " + key);
+      if (key.equals(PREFERENCES_ENTITY)) {
+        restorePreferences(data);
+      } else {
+        Log.e(MyTracksConstants.TAG, "Found unknown backup entity: " + key);
+        data.skipEntityData();
+      }
+    }
+    Log.i(MyTracksConstants.TAG, "Done restoring from backup");
+  }
+
+  /**
+   * Restores all preferences from the backup.
+   * 
+   * @param data the backup data to read from
+   * @throws IOException if there are any errors while reading
+   */
+  private void restorePreferences(BackupDataInput data) throws IOException {
+    int dataSize = data.getDataSize();
+    byte[] dataBuffer = new byte[dataSize];
+    int read = data.readEntityData(dataBuffer, 0, dataSize);
+    if (read != dataSize) {
+      throw new IOException("Failed to read all the preferences data");
+    }
+
+    SharedPreferences preferences = this.getSharedPreferences(
+        MyTracksSettings.SETTINGS_NAME, 0);
+    PreferenceBackupHelper importer = createPreferenceBackupHelper();
+    importer.importPreferences(dataBuffer, preferences);
+  }
+}

MyTracks/src/com/google/android/apps/mytracks/io/backup/MyTracksBackupAgentHelper.java

@@ -1,40 +0,0 @@
-/*
- * Copyright 2010 Google Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License"); you may not
- * use this file except in compliance with the License. You may obtain a copy of
- * the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
- * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
- * License for the specific language governing permissions and limitations under
- * the License.
- */
-package com.google.android.apps.mytracks.io.backup;
-
-import com.google.android.apps.mytracks.MyTracksSettings;
-
-import android.app.backup.BackupAgentHelper;
-import android.app.backup.SharedPreferencesBackupHelper;
-
-/**
- * Backup agent helper for mytracks.
- *
- * TODO: If/when possible, back up the database as well
- *       (see past revisions in rdamazio-mytracks-staging1 for the code)
- *
- * @author Rodrigo Damazio
- */
-public class MyTracksBackupAgentHelper extends BackupAgentHelper {
-  @Override
-  public void onCreate() {
-    super.onCreate();
-
-    addHelper("prefs",
-        new SharedPreferencesBackupHelper(
-            this, MyTracksSettings.SETTINGS_NAME));
-  }
-}