Collapse when swiping header

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

 import com.reactnativenavigation.params.ScreenParams;
 import com.reactnativenavigation.views.CollapsingContentView;
 import com.reactnativenavigation.views.LeftButtonOnClickListener;
+import com.reactnativenavigation.views.TopBar;
 import com.reactnativenavigation.views.collapsingToolbar.CollapseAmount;
 import com.reactnativenavigation.views.collapsingToolbar.CollapseCalculator;
 import com.reactnativenavigation.views.collapsingToolbar.CollapsingTopBar;
     }
 
     @Override
-    protected void createTopBar() {
+    protected TopBar createTopBar() {
         final CollapsingTopBar topBar = new CollapsingTopBar(getContext(), styleParams.collapsingTopBarParams);
         topBar.setScrollListener(getScrollListener(topBar));
-        this.topBar = topBar;
+        return topBar;
     }
 
     @Override

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

 import com.reactnativenavigation.views.CollapsingContentView;
 import com.reactnativenavigation.views.ContentView;
 import com.reactnativenavigation.views.LeftButtonOnClickListener;
+import com.reactnativenavigation.views.TopBar;
 import com.reactnativenavigation.views.collapsingToolbar.CollapseAmount;
 import com.reactnativenavigation.views.collapsingToolbar.CollapseCalculator;
 import com.reactnativenavigation.views.collapsingToolbar.CollapsingTopBar;
     }
 
     @Override
-    protected void createTopBar() {
+    protected TopBar createTopBar() {
         final CollapsingTopBar topBar = new CollapsingTopBar(getContext(), styleParams.collapsingTopBarParams);
-        topBar.setScrollListener(getScrollListener());
-        this.topBar = topBar;
+        topBar.setScrollListener(getScrollListener(topBar));
+        return topBar;
     }
 
     @Override
     }
 
     protected ContentView createContentView(PageParams tab) {
-        if (tab.hasCollapsingTopBar()) {
-            CollapsingContentView contentView = new CollapsingContentView(getContext(), tab.screenId, tab.navigationParams);
-            contentView.setViewMeasurer(new CollapsingViewPagerContentViewMeasurer((CollapsingTopBar) topBar, this, screenParams.styleParams));
-            setupCollapseDetection(contentView);
-            return contentView;
-        } else {
-            return new ContentView(getContext(), tab.screenId, tab.navigationParams);
-        }
+        CollapsingContentView contentView = new CollapsingContentView(getContext(), tab.screenId, tab.navigationParams);
+        contentView.setViewMeasurer(new CollapsingViewPagerContentViewMeasurer((CollapsingTopBar) topBar, this, screenParams.styleParams));
+        setupCollapseDetection(contentView);
+        return contentView;
     }
 
     private void setupCollapseDetection(CollapsingContentView contentView) {
-        contentView.setupCollapseDetection(getScrollListener(), new OnScrollViewAddedListener() {
+        ScrollListener scrollListener = getScrollListener((CollapsingView) topBar);
+        contentView.setupCollapseDetection(scrollListener, new OnScrollViewAddedListener() {
             @Override
             public void onScrollViewAdded(ScrollView scrollView) {
                 ((CollapsingTopBar) topBar).onScrollViewAdded(scrollView);
         });
     }
 
-    private ScrollListener getScrollListener() {
-        return new ScrollListener(new CollapseCalculator((CollapsingView) topBar, getCollapseBehaviour()),
+    private ScrollListener getScrollListener(final CollapsingView topBar) {
+        return new ScrollListener(new CollapseCalculator(topBar, getCollapseBehaviour()),
                 new OnScrollListener() {
                     @Override
                     public void onScroll(CollapseAmount amount) {
-                        ((CollapsingView) topBar).collapse(amount);
+                        topBar.collapse(amount);
                         ((CollapsingView) viewPager).collapse(amount);
                     }
 
                     @Override
                     public void onFling(CollapseAmount amount) {
-                        ((CollapsingView) topBar).collapse(amount);
+                        topBar.collapse(amount);
                         ((CollapsingView) viewPager).collapse(amount);
                     }
                 },
             }
         }
     }
+
+    protected ContentView getCurrentPage() {
+        return (ContentView) viewPager.getChildAt(viewPager.getCurrentItem());
+    }
 }

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

     }
 
     private void createAndAddTopBar() {
-        createTopBar();
+        topBar = createTopBar();
         addTopBar();
     }
 
-    protected void createTopBar() {
-        topBar = new TopBar(getContext());
+    protected TopBar createTopBar() {
+        return new TopBar(getContext());
     }
 
     private void addTopBar() {

android/app/src/main/java/com/reactnativenavigation/views/collapsingToolbar/CollapseCalculator.java

     }
 
     private boolean canCollapse(Direction direction) {
+        if (view == null) {
+            return false;
+        }
         checkCollapseLimits();
         return (isNotCollapsedOrExpended() ||
                (canCollapse && isExpendedAndScrollingUp(direction)) ||

android/app/src/main/java/com/reactnativenavigation/views/collapsingToolbar/CollapsingTopBar.java

 
 public class CollapsingTopBar extends TopBar implements CollapsingView {
     private CollapsingTopBarBackground collapsingTopBarBackground;
-    private CollapsingTopBarReactView header;
+    private CollapsingTopBarReactHeader header;
     private ScrollListener scrollListener;
     private float finalCollapsedTranslation;
     private CollapsingTopBarParams params;
 
     private void createReactView(CollapsingTopBarParams params) {
         if (params.hasReactView()) {
-            header = new CollapsingTopBarReactView(getContext(),
+            header = new CollapsingTopBarReactHeader(getContext(),
                     params.reactViewId,
                     new NavigationParams(Bundle.EMPTY),
                     scrollListener);

android/app/src/main/java/com/reactnativenavigation/views/collapsingToolbar/CollapsingTopBarReactView.java → android/app/src/main/java/com/reactnativenavigation/views/collapsingToolbar/CollapsingTopBarReactHeader.java

 import com.reactnativenavigation.params.NavigationParams;
 import com.reactnativenavigation.views.ContentView;
 
-public class CollapsingTopBarReactView extends ContentView {
+public class CollapsingTopBarReactHeader extends ContentView {
     private ScrollListener listener;
     private boolean mIsScrolling;
     private int mTouchSlop;
     private int touchDown = -1;
     private final JSTouchDispatcher mJSTouchDispatcher = new JSTouchDispatcher(this);
 
-    public CollapsingTopBarReactView(Context context, String screenId, NavigationParams navigationParams, ScrollListener scrollListener) {
+    public CollapsingTopBarReactHeader(Context context, String screenId, NavigationParams navigationParams, ScrollListener scrollListener) {
         super(context, screenId, navigationParams);
         listener = scrollListener;
         ViewConfiguration vc = ViewConfiguration.get(context);