ScrollViewAttacher

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

@@ -17,24 +17,7 @@ public class ContentView extends ReactRootView {
         startReactApplication(reactInstanceManager, moduleName, passProps);
     }
 
-    @Nullable
-    public ScrollView findScrollView() {
-        return findScrollView(this);
-    }
-
-    private ScrollView findScrollView(ViewGroup parent) {
-        for (int i = 0; i < parent.getChildCount(); i++) {
-            View child = parent.getChildAt(i);
 
-            if (child instanceof ScrollView) {
-                return (ScrollView) child;
-            } else if (child instanceof ViewGroup) {
-                return findScrollView((ViewGroup) child);
-            }
-        }
-
-        return null;
-    }
 
     @Override
     protected void onDetachedFromWindow() {

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

@@ -22,36 +22,6 @@ public class RctView extends FrameLayout {
 
     private BottomTabActivity context;
     private ReactRootView reactRootView;
-    private ScrollView scrollView;
-    private boolean isScrollEventListenerRegistered = false;
-
-    private final View.OnAttachStateChangeListener stateChangeListener =
-            new View.OnAttachStateChangeListener() {
-                @Override
-                public void onViewAttachedToWindow(View v) {
-                    scrollView = getScrollView((ViewGroup) getParent());
-
-                    if (scrollView != null && !isScrollEventListenerRegistered) {
-                        addScrollListener();
-                    }
-                }
-
-                @Override
-                public void onViewDetachedFromWindow(final View detachedView) {
-                    removeScrollListener();
-
-                    post(new Runnable() {
-                        @Override
-                        public void run() {
-                            scrollView = getScrollView((ViewGroup) getParent());
-                            if (scrollView != null && !isScrollEventListenerRegistered) {
-                                isScrollEventListenerRegistered = true;
-                                addScrollListener();
-                            }
-                        }
-                    });
-                }
-            };
 
     /**
      * Interface used to run some code when the {@link ReactRootView} is visible.
@@ -101,28 +71,6 @@ public class RctView extends FrameLayout {
         return passProps;
     }
 
-    private void setupScrollViewWithBottomTabs() {
-        scrollView = getScrollView((ViewGroup) getParent());
-        if (scrollView != null) {
-            context = (BottomTabActivity) getContext();
-            attachStateChangeListener(scrollView);
-            addScrollListener();
-        }
-    }
-
-
-    private void attachStateChangeListener(ScrollView scrollView) {
-        scrollView.addOnAttachStateChangeListener(stateChangeListener);
-    }
-
-    private void addScrollListener() {
-        scrollView.getViewTreeObserver().addOnScrollChangedListener(scrollChangedListener);
-    }
-
-    private void removeScrollListener() {
-        scrollView.getViewTreeObserver().removeOnScrollChangedListener(scrollChangedListener);
-    }
-
     /**
      * Must be called before view is removed from screen, but will be added again later. Setting mAttachScheduled
      * to true will prevent the component from getting unmounted once view is detached from screen.

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

@@ -13,7 +13,7 @@ public class ScrollDirectionListener implements ViewTreeObserver.OnScrollChanged
     }
 
     private final ViewGroup view;
-    private final OnChanged onChanged;
+    private OnChanged onChanged;
     private int lastScrollY = -1;
 
     public ScrollDirectionListener(ViewGroup view, OnChanged onChanged) {
@@ -30,10 +30,14 @@ public class ScrollDirectionListener implements ViewTreeObserver.OnScrollChanged
         final int scrollY = view.getScrollY();
         if (isScrollPositionChanged(scrollY) && !isTopOverscroll(scrollY) && !isBottomOverscroll(scrollY)) {
             lastScrollY = scrollY;
-            onChanged.onChanged(scrollY > lastScrollY ? Direction.Down : Direction.Up);
+            onChanged.onChanged(getDirection(scrollY));
         }
     }
 
+    private Direction getDirection(int scrollY) {
+        return scrollY > lastScrollY ? Direction.Down : Direction.Up;
+    }
+
     private boolean isBottomOverscroll(int scrollY) {
         return scrollY >= (view.getChildAt(0).getHeight() - view.getHeight());
     }

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

@@ -0,0 +1,72 @@
+package com.reactnativenavigation.views;
+
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.ScrollView;
+
+import com.reactnativenavigation.utils.ViewUtils;
+
+public class ScrollViewAttacher implements View.OnAttachStateChangeListener {
+
+    private final ContentView view;
+    private final ScrollDirectionListener.OnChanged onChanged;
+    private ScrollView scrollView;
+    private ScrollDirectionListener scrollDirectionListener;
+
+    public ScrollViewAttacher(ContentView view, ScrollDirectionListener.OnChanged onChanged) {
+        this.view = view;
+        this.onChanged = onChanged;
+    }
+
+    public void attach() {
+        ViewUtils.runOnPreDraw(view, new Runnable() {
+            @Override
+            public void run() {
+                findScrollAndStartListening();
+            }
+        });
+    }
+
+    public void detach() {
+        if (scrollView != null) {
+            scrollView.removeOnAttachStateChangeListener(this);
+            scrollView.getViewTreeObserver().removeOnScrollChangedListener(scrollDirectionListener);
+            scrollDirectionListener = null;
+            scrollView = null;
+        }
+    }
+
+    private void findScrollAndStartListening() {
+        scrollView = findScrollView(view);
+        if (scrollView != null) {
+            scrollDirectionListener = new ScrollDirectionListener(scrollView, onChanged);
+            scrollView.getViewTreeObserver().addOnScrollChangedListener(scrollDirectionListener);
+            scrollView.addOnAttachStateChangeListener(this);
+        }
+    }
+
+    private ScrollView findScrollView(ViewGroup parent) {
+        for (int i = 0; i < parent.getChildCount(); i++) {
+            View child = parent.getChildAt(i);
+
+            if (child instanceof ScrollView) {
+                return (ScrollView) child;
+            } else if (child instanceof ViewGroup) {
+                return findScrollView((ViewGroup) child);
+            }
+        }
+
+        return null;
+    }
+
+    @Override
+    public void onViewAttachedToWindow(View v) {
+        // nothing
+    }
+
+    @Override
+    public void onViewDetachedFromWindow(View v) {
+        detach();
+        attach();
+    }
+}