Set FragmentScreen content to fixed xml defined ID. Fixes race condition.

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

 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 
+import com.reactnativenavigation.R;
+
 import static android.view.ViewGroup.LayoutParams.MATCH_PARENT;
 
 @SuppressWarnings("ResourceType")
     @Override
     protected void createContent() {
         content = new FrameLayout(getContext());
-        content.setId(ViewUtils.generateViewId());
+        content.setId(R.id.fragment_screen_content);
         addContent();
         addFragment();
     }
     private void addFragment(Fragment fragment) {
         FragmentManager fm = activity.getFragmentManager();
         FragmentTransaction transaction = fm.beginTransaction();
-        transaction.add(content.getId(), fragment);
+        transaction.add(R.id.fragment_screen_content, fragment);
         transaction.commit();
     }
 
     private void addSupportFragment(android.support.v4.app.Fragment supportFragment) {
         android.support.v4.app.FragmentManager fm = activity.getSupportFragmentManager();
         android.support.v4.app.FragmentTransaction transaction = fm.beginTransaction();
-        transaction.add(content.getId(), supportFragment);
+        transaction.add(R.id.fragment_screen_content, supportFragment);
         transaction.commit();
     }
 

android/app/src/main/res/values/ids.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <item name="react_root_view" type="id"/>
+    <item name="fragment_screen_content" type="id"/>
 </resources>