fix #2317: NPE while backuping data

The previous fix for #2317 was incomplete, as the dependency of the
CentralBackupAgent onto Settings caused a NPE because Settings static
initializations require that an application has been created, which is
apparently not the case when a backup is launched by the OS.

The preference name has been isolated into a no-dependency package so
that the CentralBackupAgent does not depend on an application existing
anymore.

3 files changed, 26 insertions, 8 deletions

diff --git a/main/src/cgeo/geocaching/Settings.java b/main/src/cgeo/geocaching/Settings.java
index 7e6f91f..850c4f4 100644
--- a/main/src/cgeo/geocaching/Settings.java
+++ b/main/src/cgeo/geocaching/Settings.java
@@ -1359,12 +1359,6 @@ public final class Settings {
         }
     }
 
-    public static String getPreferencesName() {
-        // There is currently no Android API to get the file name of the shared preferences. Let's hardcode
-        // it without needing a cgeoapplication instance.
-        return "cgeo.geocaching_preferences";
-    }
-
     public static boolean getPlainLogs() {
         return sharedPrefs.getBoolean(KEY_PLAIN_LOGS, false);
     }
diff --git a/main/src/cgeo/geocaching/backup/CentralBackupAgent.java b/main/src/cgeo/geocaching/backup/CentralBackupAgent.java
index f6b9024..28a668c 100644
--- a/main/src/cgeo/geocaching/backup/CentralBackupAgent.java
+++ b/main/src/cgeo/geocaching/backup/CentralBackupAgent.java
@@ -1,6 +1,6 @@
 package cgeo.geocaching.backup;
 
-import cgeo.geocaching.Settings;
+import cgeo.geocaching.utils.ApplicationSettings;
 
 import android.annotation.TargetApi;
 import android.app.backup.BackupAgentHelper;
@@ -13,7 +13,7 @@ public class CentralBackupAgent extends BackupAgentHelper {
 
     @Override
     public void onCreate() {
-        final SharedPreferencesBackupHelper helper = new SharedPreferencesBackupHelper(this, Settings.getPreferencesName());
+        final SharedPreferencesBackupHelper helper = new SharedPreferencesBackupHelper(this, ApplicationSettings.getPreferencesName());
         addHelper(PREFS_BACKUP_KEY, helper);
     }
 
diff --git a/main/src/cgeo/geocaching/utils/ApplicationSettings.java b/main/src/cgeo/geocaching/utils/ApplicationSettings.java
new file mode 100644
index 0000000..99d3142
--- /dev/null
+++ b/main/src/cgeo/geocaching/utils/ApplicationSettings.java
@@ -0,0 +1,24 @@
+package cgeo.geocaching.utils;
+
+/**
+ * This utility class contains static settings that do not require a context or
+ * an application. It may not depend or use any other package from c:geo.
+ * <br/>
+ * It is used, for example, to get some settings for the BackupAgent. In this case,
+ * no application is instantiated by the OS.
+ */
+
+public class ApplicationSettings {
+
+    /**
+     * Get the name of the preferences file.
+     *
+     * @return the name of the shared preferences file without the extension
+     */
+    public static String getPreferencesName() {
+        // There is currently no Android API to get the file name of the shared preferences. Let's hardcode
+        // it without needing a cgeoapplication instance.
+        return "cgeo.geocaching_preferences";
+    }
+
+}