separate session-changed logic.

app/src/main/java/chat/rocket/android/activity/MainActivity.java

@@ -149,7 +149,11 @@ public class MainActivity extends AbstractAuthedActivity {
         .createObjectObserver(realm ->
             Session.queryDefaultSession(realm)
                 .isNotNull(Session.TOKEN))
-        .setOnUpdateListener(session -> {
+        .setOnUpdateListener(this::onSessionChanged);
+    sessionObserver.sub();
+  }
+
+  private void onSessionChanged(@Nullable Session session) {
     if (session == null) {
       if (isForeground) {
         LaunchUtil.showLoginActivity(this, serverConfigId);
@@ -178,8 +182,6 @@ public class MainActivity extends AbstractAuthedActivity {
     } else {
       tipViewManager.updateStatus(StatusTicker.STATUS_DISMISS, null);
     }
-        });
-    sessionObserver.sub();
   }
 
   private void updateSidebarMainFragment() {