added portraitOnlyMode

android/app/src/main/AndroidManifest.xml

         android:allowBackup="false"
         android:theme="@style/Theme.AppCompat.Light.NoActionBar">
         <activity android:name=".controllers.NavigationActivity" />
+        <activity
+            android:name=".controllers.PortraitNavigationActivity"
+            android:screenOrientation="portrait" />
         <activity
             android:name="com.facebook.react.devsupport.DevSettingsActivity"
             android:exported="false" />

android/app/src/main/java/com/reactnativenavigation/bridge/NavigationReactModule.java

 
     @ReactMethod
     public void startApp(final ReadableMap params) {
-        NavigationCommandsHandler.startApp(BundleConverter.toBundle(params));
+        boolean portraitOnlyMode = false;
+        if (params.hasKey("portraitOnlyMode")) {
+            portraitOnlyMode = params.getBoolean("portraitOnlyMode");
+        }
+        NavigationCommandsHandler.startApp(BundleConverter.toBundle(params), portraitOnlyMode);
     }
 
     @ReactMethod

android/app/src/main/java/com/reactnativenavigation/controllers/NavigationCommandsHandler.java

      *
      * @param params ActivityParams as bundle
      */
-    public static void startApp(Bundle params) {
-        Intent intent = new Intent(NavigationApplication.instance, NavigationActivity.class);
+    public static void startApp(Bundle params, boolean portraitOnlyMode) {
+        Intent intent;
+        if (portraitOnlyMode) {
+            intent = new Intent(NavigationApplication.instance, PortraitNavigationActivity.class);
+        } else {
+            intent = new Intent(NavigationApplication.instance, NavigationActivity.class);
+        }
         intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
         intent.putExtra(ACTIVITY_PARAMS_BUNDLE, params);
         NavigationApplication.instance.startActivity(intent);
     }
 
     public static void setScreenTitleBarLeftButtons(final String screenInstanceId,
-                                                     final String navigatorEventId,
-                                                     final TitleBarLeftButtonParams titleBarButtons) {
+                                                    final String navigatorEventId,
+                                                    final TitleBarLeftButtonParams titleBarButtons) {
         final NavigationActivity currentActivity = NavigationActivity.currentActivity;
         if (currentActivity == null) {
             return;

android/app/src/main/java/com/reactnativenavigation/controllers/PortraitNavigationActivity.java

+package com.reactnativenavigation.controllers;
+
+public class PortraitNavigationActivity extends NavigationActivity {
+}

example/src/app.js

     left: {
       screen: 'example.SideMenu'
     }
-  }
+  },
+  portraitOnlyMode: true
 });
-// Navigation.startSingleScreenApp({
-//   screen: {
-//     screen: 'example.FirstTabScreen',
-//     title: 'Navigation',
-//     navigatorStyle: {
-//       navBarBackgroundColor: '#4dbce9',
-//       navBarTextColor: '#ffff00',
-//       navBarSubtitleTextColor: '#ff0000',
-//       navBarButtonColor: '#ffffff',
-//       statusBarTextColorScheme: 'light'
-//     }
-//   },
-//   drawer: {
-//     left: {
-//       screen: 'example.SideMenu'
-//     }
-//   }
-// });
+//Navigation.startSingleScreenApp({
+//  screen: {
+//    screen: 'example.FirstTabScreen',
+//    title: 'Navigation',
+//    navigatorStyle: {
+//      navBarBackgroundColor: '#4dbce9',
+//      navBarTextColor: '#ffff00',
+//      navBarSubtitleTextColor: '#ff0000',
+//      navBarButtonColor: '#ffffff',
+//      statusBarTextColorScheme: 'light'
+//    }
+//  },
+//  drawer: {
+//    left: {
+//      screen: 'example.SideMenu'
+//    }
+//  }
+//});