Going down the BottomSheetBehavior rabbit hole...

BottomSheetBehavior only supports one scrolling child. Add support for a ViewPager.
ViewPager.getChildAt sometimes does not match the actual position.
Make sure that it keeps all children using setOffscreenPageLimit

1 files changed, 75 insertions, 0 deletions

diff --git a/app/src/main/java/com/google/android/material/bottomsheet/ViewPagerBottomSheetBehavior.java b/app/src/main/java/com/google/android/material/bottomsheet/ViewPagerBottomSheetBehavior.java
new file mode 100644
index 000000000..2d211704d
--- /dev/null
+++ b/app/src/main/java/com/google/android/material/bottomsheet/ViewPagerBottomSheetBehavior.java
@@ -0,0 +1,75 @@
+package com.google.android.material.bottomsheet;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.view.View;
+import android.view.ViewGroup;
+import androidx.coordinatorlayout.widget.CoordinatorLayout;
+import androidx.core.view.ViewCompat;
+import androidx.viewpager.widget.ViewPager;
+
+import java.lang.ref.WeakReference;
+
+/**
+ * Override {@link #findScrollingChild(View)} to support {@link ViewPager}'s nested scrolling.
+ * By the way, In order to override package level method and field.
+ * This class put in the same package path where {@link BottomSheetBehavior} located.
+ * Source: https://medium.com/@hanru.yeh/funny-solution-that-makes-bottomsheetdialog-support-viewpager-with-nestedscrollingchilds-bfdca72235c3
+ */
+public class ViewPagerBottomSheetBehavior<V extends View> extends BottomSheetBehavior<V> {
+
+    public ViewPagerBottomSheetBehavior() {
+        super();
+    }
+
+    public ViewPagerBottomSheetBehavior(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    @Override
+    View findScrollingChild(View view) {
+        if (ViewCompat.isNestedScrollingEnabled(view)) {
+            return view;
+        }
+
+        if (view instanceof ViewPager) {
+            ViewPager viewPager = (ViewPager) view;
+            View currentViewPagerChild = viewPager.getChildAt(viewPager.getCurrentItem());
+            return findScrollingChild(currentViewPagerChild);
+        } 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));
+                if (scrollingChild != null) {
+                    return scrollingChild;
+                }
+            }
+        }
+        return null;
+    }
+
+    public void updateScrollingChild() {
+        final View scrollingChild = findScrollingChild(viewRef.get());
+        nestedScrollingChildRef = new WeakReference<>(scrollingChild);
+    }
+
+    /**
+     * A utility function to get the {@link ViewPagerBottomSheetBehavior} associated with the {@code view}.
+     *
+     * @param view The {@link View} with {@link ViewPagerBottomSheetBehavior}.
+     * @return The {@link ViewPagerBottomSheetBehavior} associated with the {@code view}.
+     */
+    @SuppressWarnings("unchecked")
+    public static <V extends View> ViewPagerBottomSheetBehavior<V> from(V view) {
+        ViewGroup.LayoutParams params = view.getLayoutParams();
+        if (!(params instanceof CoordinatorLayout.LayoutParams)) {
+            throw new IllegalArgumentException("The view is not a child of CoordinatorLayout");
+        }
+        CoordinatorLayout.Behavior behavior = ((CoordinatorLayout.LayoutParams) params).getBehavior();
+        if (!(behavior instanceof ViewPagerBottomSheetBehavior)) {
+            throw new IllegalArgumentException(
+                    "The view is not associated with ViewPagerBottomSheetBehavior");
+        }
+        return (ViewPagerBottomSheetBehavior<V>) behavior;
+    }
+}
\ No newline at end of file