Android 自定义FooterBarLayout中没有要跟随AppBarLayout的滚动条

我有以下协调布局行为：

public class FooterBarBehavior extends CoordinatorLayout.Behavior<FooterBarLayout> {
    //Required to instantiate as a default behavior
    public FooterBarBehavior() {
    }

    //Required to attach behavior via XML
    public FooterBarBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    //This is called to determine which views this behavior depends on
    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent,
                                   FooterBarLayout child,
                                   View dependency) {
        //We are watching changes in the AppBarLayout
        return getDependentView((ViewPager) dependency) instanceof AppBarLayout;
    }

    //This is called for each change to a dependent view
    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent,
                                          FooterBarLayout child,
                                          View dependency) {
        int offset = -getDependentView((ViewPager) dependency).getTop();
        child.setTranslationY(offset);
        return true;
    }

    private View getDependentView(ViewPager viewPager) {
        int index = viewPager.getCurrentItem();
        MainPagerAdapter adapter = ((MainPagerAdapter)viewPager.getAdapter());
        ContactsFragment fragment = (ContactsFragment) adapter.getItem(index);
        if(fragment.getView() == null) {
            return null;
        }
        return fragment.getView().findViewById(R.id.appBarLayout);
    }
}

它已在布局中使用，如下所示：

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    tools:context=".ui.MainActivity">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

        <com.sample.android.contact.widget.FooterBarLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content">

            <com.sample.android.contact.widget.ListenableTabLayout
                android:id="@+id/tab_layout"
                android:layout_width="match_parent"
                android:layout_height="48dp"
                android:layout_alignParentBottom="true"
                android:background="@drawable/rectangle_shape"
                app:tabIndicatorHeight="2dp"
                app:tabSelectedTextColor="@color/color1" />

        <ImageView
            android:id="@+id/triangle"
            android:layout_width="30dp"
            android:layout_height="30dp"
            android:layout_above="@+id/tab_layout"
            android:layout_marginBottom="@dimen/dimen_triangle_bottom_margin"
            android:src="@drawable/triangle_shape"
            tools:ignore="ContentDescription" />

    </com.sample.android.contact.widget.FooterBarLayout>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

但在FooterBarLayout中不会滚动。你们有办法解决这个问题吗

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    tools:context=".ui.MainActivity">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

        <com.sample.android.contact.widget.FooterBarLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content">

            <com.sample.android.contact.widget.ListenableTabLayout
                android:id="@+id/tab_layout"
                android:layout_width="match_parent"
                android:layout_height="48dp"
                android:layout_alignParentBottom="true"
                android:background="@drawable/rectangle_shape"
                app:tabIndicatorHeight="2dp"
                app:tabSelectedTextColor="@color/color1" />

        <ImageView
            android:id="@+id/triangle"
            android:layout_width="30dp"
            android:layout_height="30dp"
            android:layout_above="@+id/tab_layout"
            android:layout_marginBottom="@dimen/dimen_triangle_bottom_margin"
            android:src="@drawable/triangle_shape"
            tools:ignore="ContentDescription" />

    </com.sample.android.contact.widget.FooterBarLayout>

</androidx.coordinatorlayout.widget.CoordinatorLayout>