Alert before trying to downgrade

res/values/strings.xml

@@ -5,6 +5,7 @@
     <string name="searchres_noapps">No applications were found matching \'%s\'</string>
     <string name="SignatureMismatch">The new version is signed with a different key to the old one. To install the new version, the old one must be uninstalled first. Please do this and try again. (Note that uninstalling will erase any internal data stored by the application)</string>
     <string name="installIncompatible">Android says this package is not compatible with your device. Do you want to try and install it anyway?</string>
+    <string name="installDowngrade">You are trying to downgrade this application. Doing so might get it to malfunction and even lose your data. Do you want to try and downgrade it anyway?</string>
 	<string name="version">Version</string>
 	<string name="n_versions_available">%d versions available</string>
 	<string name="n_version_available">%d version available</string>

src/org/fdroid/fdroid/AppDetails.java

@@ -475,7 +475,26 @@ public class AppDetails extends ListActivity {
         curapk = app.apks.get(position - l.getHeaderViewsCount());
         if (app.installedVerCode == curapk.vercode)
             removeApk(app.id);
-        else
+        else if (app.installedVerCode > curapk.vercode) {
+            AlertDialog.Builder ask_alrt = new AlertDialog.Builder(this);
+            ask_alrt.setMessage(getString(R.string.installDowngrade));
+            ask_alrt.setPositiveButton(getString(R.string.yes),
+                    new DialogInterface.OnClickListener() {
+                        public void onClick(DialogInterface dialog,
+                                int whichButton) {
+                            install();
+                        }
+                    });
+            ask_alrt.setNegativeButton(getString(R.string.no),
+                    new DialogInterface.OnClickListener() {
+                        public void onClick(DialogInterface dialog,
+                                int whichButton) {
+                            return;
+                        }
+                    });
+            AlertDialog alert = ask_alrt.create();
+            alert.show();
+        } else
             install();
     }