fix #3186: do not try to install a null map source

If the wanted map source can no longer be found (because it has been
made unavaiable on the device), try to install a default one, or
fail silently with an error message in the log.

2 files changed, 28 insertions, 1 deletions

diff --git a/main/src/cgeo/geocaching/maps/MapProviderFactory.java b/main/src/cgeo/geocaching/maps/MapProviderFactory.java
index 84c9329..a03fc47 100644
--- a/main/src/cgeo/geocaching/maps/MapProviderFactory.java
+++ b/main/src/cgeo/geocaching/maps/MapProviderFactory.java
@@ -69,6 +69,12 @@ public class MapProviderFactory {
         parentMenu.setGroupCheckable(R.id.menu_group_map_sources, true, true);
     }
 
+    /**
+     * Return a map source by id.
+     *
+     * @param id the map source id
+     * @return the map source, or <tt>null</tt> if <tt>id</tt> does not correspond to a registered map source
+     */
     public static MapSource getMapSource(int id) {
         for (MapSource mapSource : mapSources) {
             if (mapSource.getNumericalId() == id) {
@@ -78,6 +84,15 @@ public class MapProviderFactory {
         return null;
     }
 
+    /**
+     * Return a map source if there is at least one.
+     *
+     * @return the first map source in the collection, or <tt>null</tt> if there are none registered
+     */
+    public static MapSource getAnyMapSource() {
+        return mapSources.isEmpty() ? null : mapSources.get(0);
+    }
+
     public static void registerMapSource(final MapSource mapSource) {
         mapSources.add(mapSource);
     }
diff --git a/main/src/cgeo/geocaching/settings/SettingsActivity.java b/main/src/cgeo/geocaching/settings/SettingsActivity.java
index 42f6074..ece2acb 100644
--- a/main/src/cgeo/geocaching/settings/SettingsActivity.java
+++ b/main/src/cgeo/geocaching/settings/SettingsActivity.java
@@ -40,6 +40,7 @@ import android.view.View;
 import android.widget.BaseAdapter;
 import android.widget.EditText;
 import android.widget.ListAdapter;
+import android.widget.Toast;
 
 import java.io.File;
 import java.util.ArrayList;
@@ -482,7 +483,18 @@ public class SettingsActivity extends PreferenceActivity {
             } else if (isPreference(preference, R.string.pref_mapsource)) {
                 // reset the cached map source
                 int mapSourceId = Integer.valueOf(stringValue);
-                final MapSource mapSource = MapProviderFactory.getMapSource(mapSourceId);
+                MapSource mapSource = MapProviderFactory.getMapSource(mapSourceId);
+                // If there is no corresponding map source (because some map sources were
+                // removed from the device since) then use the first one available.
+                if (mapSource == null) {
+                    mapSource = MapProviderFactory.getAnyMapSource();
+                    if (mapSource == null) {
+                        // There are no map source. There is little we can do here, except log an error and
+                        // return to avoid triggering a null pointer exception.
+                        Log.e("SettingsActivity.onPreferenceChange: no map source available");
+                        return true;
+                    }
+                }
                 Settings.setMapSource(mapSource);
                 preference.setSummary(mapSource.getName());
             } else if (isPreference(preference, R.string.pref_connectorOCActive) || isPreference(preference, R.string.pref_connectorOCPLActive) || isPreference(preference, R.string.pref_connectorGCActive)) {