Add selectedTabChanged event

android/app/src/main/java/com/reactnativenavigation/NavigationApplication.java

         navigationReactInstance.getReactEventEmitter().sendNavigatorEvent(eventId, navigatorEventId);
     }
 
+    public void sendNavigatorEvent(String eventId, String navigatorEventId, WritableMap data) {
+        if (navigationReactInstance == null) {
+            return;
+        }
+        navigationReactInstance.getReactEventEmitter().sendNavigatorEvent(eventId, navigatorEventId, data);
+    }
+
     public void sendEvent(String eventId, String navigatorEventId) {
         if (navigationReactInstance == null) {
             return;

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

         eventEmitter.emit(navigatorEventId, data);
     }
 
+    public void sendNavigatorEvent(String eventId, String navigatorEventId, WritableMap data) {
+        data.putString(KEY_NAVIGATOR_EVENT_ID, navigatorEventId);
+        data.putString(KEY_EVENT_ID, eventId);
+        eventEmitter.emit(navigatorEventId, data);
+    }
+
     public void sendEvent(String eventId, String data) {
         eventEmitter.emit(eventId, data);
     }

android/app/src/main/java/com/reactnativenavigation/params/TopTabParams.java

 public class TopTabParams {
     public String screenId;
     public String title;
-    public String screenInstanceId;
     public Bundle passProps;
 }

android/app/src/main/java/com/reactnativenavigation/params/parsers/TopTabParamsParser.java

 
 public class TopTabParamsParser extends Parser {
     private static final String KEY_SCREEN_ID = "screenId";
-    private static final String KEY_SCREEN_INSTANCE_ID = "screenInstanceID";
     private static final String KEY_TITLE = "title";
     private static final String KEY_PROPS = "passProps";
 
     private static TopTabParams parseItem(Bundle params) {
         TopTabParams result = new TopTabParams();
         result.screenId = params.getString(KEY_SCREEN_ID);
-        result.screenInstanceId = params.getString(KEY_SCREEN_INSTANCE_ID);
         result.title = params.getString(KEY_TITLE);
         result.passProps = params.getBundle(KEY_PROPS);
         return result;

android/app/src/main/java/com/reactnativenavigation/screens/ContentViewPagerAdapter.java

+package com.reactnativenavigation.screens;
+
+import android.support.v4.view.PagerAdapter;
+import android.view.View;
+import android.view.ViewGroup;
+
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.WritableMap;
+import com.reactnativenavigation.NavigationApplication;
+import com.reactnativenavigation.params.TopTabParams;
+import com.reactnativenavigation.views.ContentView;
+
+import java.util.List;
+
+public class ContentViewPagerAdapter extends PagerAdapter {
+
+    private List<ContentView> contentViews;
+    private List<TopTabParams> topTabParams;
+    private int currentPosition = 0;
+
+    public ContentViewPagerAdapter(List<ContentView> contentViews, List<TopTabParams> topTabParams) {
+        this.contentViews = contentViews;
+        this.topTabParams = topTabParams;
+    }
+
+    @Override
+    public Object instantiateItem(ViewGroup container, int position) {
+        return contentViews.get(position);
+    }
+
+    @Override
+    public void setPrimaryItem(ViewGroup container, int position, Object object) {
+        super.setPrimaryItem(container, position, object);
+        if (position != currentPosition) {
+            currentPosition = position;
+            sendPageChangeEvent();
+        }
+    }
+
+    private void sendPageChangeEvent() {
+        WritableMap data = Arguments.createMap();
+        String navigatorEventId = contentViews.get(currentPosition).getNavigatorEventId();
+        data.putInt("position", currentPosition);
+        NavigationApplication.instance.sendNavigatorEvent("selectedTabChanged", navigatorEventId, data);
+    }
+
+    @Override
+    public int getCount() {
+        return contentViews.size();
+    }
+
+    @Override
+    public boolean isViewFromObject(View view, Object object) {
+        return view == object;
+    }
+
+    @Override
+    public CharSequence getPageTitle(int position) {
+        return topTabParams.get(position).title;
+    }
+}

android/app/src/main/java/com/reactnativenavigation/screens/FragmentScreen.java

     }
 
     private void addContent() {
-        ContentView contentView = new ContentView(getContext(),
-                screenParams.screenId,
-                screenParams.passProps,
-                screenParams.navigationParams);
+        ContentView contentView = new ContentView(getContext(), screenParams, screenParams.screenId);
         addView(contentView, 0, 0);
         LayoutParams params = new LayoutParams(MATCH_PARENT, MATCH_PARENT);
         if (screenParams.styleParams.drawScreenBelowTopBar) {

android/app/src/main/java/com/reactnativenavigation/screens/SingleScreen.java

 
     @Override
     protected void createContent() {
-        contentView = new ContentView(getContext(),
-                screenParams.screenId,
-                screenParams.passProps,
-                screenParams.navigationParams);
+        contentView = new ContentView(getContext(), screenParams, screenParams.screenId);
         LayoutParams params = new LayoutParams(MATCH_PARENT, MATCH_PARENT);
         if (screenParams.styleParams.drawScreenBelowTopBar) {
             params.addRule(BELOW, topBar.getId());

android/app/src/main/java/com/reactnativenavigation/screens/ViewPagerScreen.java

 package com.reactnativenavigation.screens;
 
 import android.support.design.widget.TabLayout;
-import android.support.v4.view.PagerAdapter;
 import android.support.v4.view.ViewPager;
 import android.support.v7.app.AppCompatActivity;
-import android.view.View;
-import android.view.ViewGroup;
 
 import com.reactnativenavigation.params.ScreenParams;
 import com.reactnativenavigation.params.TopTabParams;
 
 public class ViewPagerScreen extends Screen {
 
+    private static final int OFFSCREEN_PAGE_LIMIT = 99;
     private List<ContentView> contentViews;
     private ViewPager viewPager;
 
 
     private void createViewPager() {
         viewPager = new ViewPager(getContext());
-        viewPager.setOffscreenPageLimit(99);
+        viewPager.setOffscreenPageLimit(OFFSCREEN_PAGE_LIMIT);
         LayoutParams lp = new LayoutParams(MATCH_PARENT, MATCH_PARENT);
         if (screenParams.styleParams.drawScreenBelowTopBar) {
             lp.addRule(BELOW, topBar.getId());
     private void addPages() {
         contentViews = new ArrayList<>();
         for (TopTabParams topTabParam : screenParams.topTabParams) {
-            ContentView contentView = new ContentView(getContext(),
-                    topTabParam.screenId,
-                    screenParams.passProps,
-                    screenParams.navigationParams);
+            ContentView contentView = new ContentView(getContext(), screenParams, topTabParam.screenId);
             addContent(contentView);
             contentViews.add(contentView);
         }
     }
 
     private void setupViewPager(TabLayout tabLayout) {
-        ContentViewPagerAdapter adapter =
-                new ContentViewPagerAdapter(viewPager, contentViews, screenParams.topTabParams);
+        ContentViewPagerAdapter adapter = new ContentViewPagerAdapter(contentViews, screenParams.topTabParams);
         viewPager.setAdapter(adapter);
         tabLayout.setupWithViewPager(viewPager);
     }
             contentView.preventMountAfterReattachedToWindow();
         }
     }
-
-    public class ContentViewPagerAdapter extends PagerAdapter implements TabLayout.OnTabSelectedListener, ViewPager.OnPageChangeListener {
-
-        private ViewPager viewPager;
-        private List<ContentView> contentViews;
-        private List<TopTabParams> topTabParams;
-
-        public ContentViewPagerAdapter(ViewPager viewPager, List<ContentView> contentViews, List<TopTabParams> topTabParams) {
-            this.viewPager = viewPager;
-            this.contentViews = contentViews;
-            this.topTabParams = topTabParams;
-        }
-
-        @Override
-        public Object instantiateItem(ViewGroup container, int position) {
-            return contentViews.get(position);
-        }
-
-        @Override
-        public void destroyItem(ViewGroup container, int position, Object view) {
-
-        }
-
-        @Override
-        public int getCount() {
-            return contentViews.size();
-        }
-
-        @Override
-        public boolean isViewFromObject(View view, Object object) {
-            return view == object;
-        }
-
-        @Override
-        public CharSequence getPageTitle(int position) {
-            return topTabParams.get(position).title;
-        }
-
-        @Override
-        public void onTabSelected(TabLayout.Tab tab) {
-            int position = tab.getPosition();
-            viewPager.setCurrentItem(position);
-        }
-
-        @Override
-        public void onTabUnselected(TabLayout.Tab tab) {
-
-        }
-
-        @Override
-        public void onTabReselected(TabLayout.Tab tab) {
-
-        }
-
-        @Override
-        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
-
-        }
-
-        @Override
-        public void onPageSelected(int position) {
-
-        }
-
-        @Override
-        public void onPageScrollStateChanged(int state) {
-
-        }
-    }
 }

android/app/src/main/java/com/reactnativenavigation/views/ContentView.java

 import com.facebook.react.ReactInstanceManager;
 import com.facebook.react.ReactRootView;
 import com.reactnativenavigation.NavigationApplication;
+import com.reactnativenavigation.params.ScreenParams;
 import com.reactnativenavigation.react.ReactViewHacks;
 
 public class ContentView extends ReactRootView {
 
     private final String screenId;
+    private final String navigatorEventId;
     private final Bundle passProps;
     private Bundle navigationParams;
 
-    public ContentView(Context context, final String screenId, Bundle passProps, Bundle navigationParams) {
+    public ContentView(Context context, ScreenParams screenParams, String screenId) {
         super(context);
         this.screenId = screenId;
-        this.passProps = passProps;
-        this.navigationParams = navigationParams;
-        attachToJS();
-    }
+        navigatorEventId = screenParams.navigatorEventId;
 
-    private void attachToJS() {
-        ReactInstanceManager react = NavigationApplication.instance.getNavigationReactInstance().getReactInstanceManager();
-        startReactApplication(react, screenId, mergePropsAndNavigationParams());
+        passProps = screenParams.passProps;
+        navigationParams = screenParams.navigationParams;
+        attachToJS();
     }
 
-    private Bundle mergePropsAndNavigationParams() {
-        if (passProps != null) {
-            navigationParams.putAll(passProps);
-        }
-        return navigationParams;
+    public String getNavigatorEventId() {
+        return navigatorEventId;
     }
 
     public void preventUnmountOnDetachedFromWindow() {
     public void preventMountAfterReattachedToWindow() {
         ReactViewHacks.preventMountAfterReattachedToWindow(this);
     }
+
+    private void attachToJS() {
+        ReactInstanceManager react = NavigationApplication.instance.getNavigationReactInstance().getReactInstanceManager();
+        startReactApplication(react, screenId, mergePropsAndNavigationParams());
+    }
+
+    private Bundle mergePropsAndNavigationParams() {
+        if (passProps != null) {
+            navigationParams.putAll(passProps);
+        }
+        return navigationParams;
+    }
 }