modify behavior and provide convenience tools

vpbs/src/main/java/android/support/v4/view/ViewPagerUtils.java

@@ -0,0 +1,19 @@
+package android.support.v4.view;
+
+import android.view.View;
+
+public class ViewPagerUtils {
+
+    public static View getCurrentView(ViewPager viewPager) {
+        final int currentItem = viewPager.getCurrentItem();
+        for (int i = 0; i < viewPager.getChildCount(); i++) {
+            final View child = viewPager.getChildAt(i);
+            final ViewPager.LayoutParams layoutParams = (ViewPager.LayoutParams) child.getLayoutParams();
+            if (!layoutParams.isDecor && currentItem == layoutParams.position) {
+                return child;
+            }
+        }
+        return null;
+    }
+
+}

vpbs/src/main/java/biz/laenger/android/vpbs/BottomSheetUtils.java

@@ -0,0 +1,51 @@
+package biz.laenger.android.vpbs;
+
+import android.support.design.widget.CoordinatorLayout;
+import android.support.v4.view.ViewPager;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.ViewParent;
+
+public final class BottomSheetUtils {
+
+    public static void setupViewPager(ViewPager viewPager) {
+        final View bottomSheetParent = findBottomSheetParent(viewPager);
+        if (bottomSheetParent != null) {
+            viewPager.addOnPageChangeListener(new BottomSheetViewPagerListener(viewPager, bottomSheetParent));
+        }
+    }
+
+    private static class BottomSheetViewPagerListener extends ViewPager.SimpleOnPageChangeListener {
+        private final ViewPager viewPager;
+        private final ViewPagerBottomSheetBehavior<View> behavior;
+
+        public BottomSheetViewPagerListener(ViewPager viewPager, View bottomSheetParent) {
+            this.viewPager = viewPager;
+            this.behavior = ViewPagerBottomSheetBehavior.from(bottomSheetParent);
+        }
+
+        @Override
+        public void onPageSelected(int position) {
+            viewPager.post(new Runnable() {
+                @Override
+                public void run() {
+                    behavior.invalidateScrollingChild();
+                }
+            });
+        }
+    }
+
+    private static View findBottomSheetParent(final View view) {
+        View current = view;
+        while (current != null) {
+            final ViewGroup.LayoutParams params = current.getLayoutParams();
+            if (params instanceof CoordinatorLayout.LayoutParams && ((CoordinatorLayout.LayoutParams) params).getBehavior() instanceof ViewPagerBottomSheetBehavior) {
+                return current;
+            }
+            final ViewParent parent = current.getParent();
+            current = parent == null || !(parent instanceof View) ? null : (View) parent;
+        }
+        return null;
+    }
+
+}

vpbs/src/main/java/biz/laenger/android/vpbs/ViewPagerBottomSheetBehavior.java

@@ -31,6 +31,8 @@
 import android.support.v4.view.NestedScrollingChild;
 import android.support.v4.view.VelocityTrackerCompat;
 import android.support.v4.view.ViewCompat;
+import android.support.v4.view.ViewPager;
+import android.support.v4.view.ViewPagerUtils;
 import android.support.v4.widget.ViewDragHelper;
 import android.util.AttributeSet;
 import android.view.MotionEvent;
@@ -391,6 +393,11 @@ public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, V child, Vi
                                 velocityX, velocityY));
     }
 
+    void invalidateScrollingChild() {
+        final View scrollingChild = findScrollingChild(mViewRef.get());
+        mNestedScrollingChildRef = new WeakReference<>(scrollingChild);
+    }
+
     /**
      * Sets the height of the bottom sheet when it is collapsed.
      *
@@ -548,7 +555,14 @@ private View findScrollingChild(View view) {
         if (view instanceof NestedScrollingChild) {
             return view;
         }
-        if (view instanceof ViewGroup) {
+        if (view instanceof ViewPager) {
+            ViewPager viewPager = (ViewPager) view;
+            View currentViewPagerChild = ViewPagerUtils.getCurrentView(viewPager);
+            View scrollingChild = findScrollingChild(currentViewPagerChild);
+            if (scrollingChild != null) {
+                return scrollingChild;
+            }
+        } else if (view instanceof ViewGroup) {
             ViewGroup group = (ViewGroup) view;
             for (int i = 0, count = group.getChildCount(); i < count; i++) {
                 View scrollingChild = findScrollingChild(group.getChildAt(i));