Update left button navigatorEventId when changing TopTabs (#1269)

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

         }
         if (ViewPagerScreenChangedEvent.TYPE.equals(event.getType()) && isShown() ) {
             topBar.dismissContextualMenu();
+            topBar.onViewPagerScreenChanged(getScreenParams());
         }
     }
 
         topBar.addTitleBarAndSetButtons(screenParams.rightButtons,
                 screenParams.leftButton,
                 leftButtonOnClickListener,
-                screenParams.getNavigatorEventId(),
+                getNavigatorEventId(),
                 screenParams.overrideBackPressInJs);
     }
 

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

     public void setScreenTitleBarLeftButton(String screenInstanceId, final String navigatorEventId, final TitleBarLeftButtonParams titleBarLeftButtonParams) {
         performOnScreen(screenInstanceId, new Task<Screen>() {
             @Override
-            public void run(Screen param) {
-                param.setTitleBarLeftButton(navigatorEventId, leftButtonOnClickListener, titleBarLeftButtonParams);
+            public void run(Screen screen) {
+                screen.setTitleBarLeftButton(navigatorEventId, leftButtonOnClickListener, titleBarLeftButtonParams);
             }
         });
     }

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

 import com.reactnativenavigation.params.FabParams;
 import com.reactnativenavigation.params.PageParams;
 import com.reactnativenavigation.params.ScreenParams;
+import com.reactnativenavigation.params.TitleBarLeftButtonParams;
 import com.reactnativenavigation.views.ContentView;
 import com.reactnativenavigation.views.LeftButtonOnClickListener;
 import com.reactnativenavigation.views.TopTabs;
 
     @Override
     public BaseScreenParams getScreenParams() {
-        return screenParams.topTabParams.get(viewPager.getCurrentItem());
+        return screenParams.topTabParams.get(getCurrentItem());
+    }
+
+    @Override
+    public void setTitleBarLeftButton(String navigatorEventId, LeftButtonOnClickListener backButtonListener, TitleBarLeftButtonParams titleBarLeftButtonParams) {
+        super.setTitleBarLeftButton(getNavigatorEventId(), backButtonListener, titleBarLeftButtonParams);
     }
 
     @Override
 
     @Override
     public ContentView getContentView() {
-        return contentViews.get(viewPager.getCurrentItem());
+        return contentViews.get(getCurrentItem());
     }
 
     @Override
 
     @Override
     public String getScreenInstanceId() {
-        return screenParams.topTabParams.get(viewPager.getCurrentItem()).navigationParams.screenInstanceId;
+        return screenParams.topTabParams.get(getCurrentItem()).navigationParams.screenInstanceId;
     }
 
     @Override
     public String getNavigatorEventId() {
-        return screenParams.topTabParams.get(viewPager.getCurrentItem()).navigationParams.navigatorEventId;
+        return screenParams.topTabParams.get(getCurrentItem()).navigationParams.navigatorEventId;
+    }
+
+    private int getCurrentItem() {
+        return viewPager == null ? 0 : viewPager.getCurrentItem();
     }
 
     public void selectTopTabByTabIndex(int index) {

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

 
     private TitleBarLeftButtonParams params;
     private final LeftButtonOnClickListener onClickListener;
-    private final String navigatorEventId;
+    private String navigatorEventId;
     private final boolean overrideBackPressInJs;
 
     LeftButton(Context context,
     private void sendClickEvent() {
         NavigationApplication.instance.getEventEmitter().sendNavigatorEvent(params.eventId, navigatorEventId);
     }
+
+    void updateNavigatorEventId(String navigatorEventId) {
+        this.navigatorEventId = navigatorEventId;
+    }
 }

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

 import android.view.animation.AccelerateInterpolator;
 import android.widget.TextView;
 
+import com.reactnativenavigation.params.BaseScreenParams;
 import com.reactnativenavigation.params.BaseTitleBarButtonParams;
 import com.reactnativenavigation.params.StyleParams;
 import com.reactnativenavigation.params.TitleBarButtonParams;
     BaseTitleBarButtonParams getButton(int index) {
         return rightButtons.get(rightButtons.size() - index - 1);
     }
+
+    public void onViewPagerScreenChanged(BaseScreenParams screenParams) {
+        if (hasLeftButton()) {
+            leftButton.updateNavigatorEventId(screenParams.getNavigatorEventId());
+        }
+    }
 }

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

 import android.widget.FrameLayout;
 
 import com.facebook.react.bridge.Callback;
+import com.reactnativenavigation.params.BaseScreenParams;
 import com.reactnativenavigation.params.ContextualMenuParams;
 import com.reactnativenavigation.params.StyleParams;
 import com.reactnativenavigation.params.TitleBarButtonParams;
     public void destroy() {
 
     }
+
+    public void onViewPagerScreenChanged(BaseScreenParams screenParams) {
+        titleBar.onViewPagerScreenChanged(screenParams);
+    }
 }