CoordinatorLayout内的Viewpager不滚动“折叠”工具栏

Question

I am trying to implement the parallax effect with for my layout. It works, however I need one more thing. Here is my code

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/coordinator_layout_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar_layout_main"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:fitsSystemWindows="true"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsing_toolbar_main"
            android:layout_width="match_parent"
            android:layout_height="@dimen/height_toolbar_header_experiment_result"
            app:contentScrim="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|exitUntilCollapsed|snap"
            app:titleEnabled="false">

            <ImageView
                android:id="@+id/image_view_tab_header"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:background="@drawable/experiment_result_header"
                android:fitsSystemWindows="true"
                android:scaleType="centerCrop"
                app:layout_collapseMode="parallax"/>

            <View
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:alpha="0.3"
                android:background="@android:color/black"
                android:fitsSystemWindows="true"/>

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar_tab_layout"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:layout_gravity="top"
                android:layout_marginBottom="?actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

            <android.support.design.widget.TabLayout
                android:id="@+id/tab_layout_main"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="bottom"
                app:tabIndicatorColor="@android:color/white"
                app:tabSelectedTextColor="@android:color/white"
                app:tabTextColor="@color/whitesmoke"/>

        </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/view_pager_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"/>

</android.support.design.widget.CoordinatorLayout>

This works fine, however I am only able to scroll/collapse toolber while swiping the header ImageView (image_view_tab_header). When I try to swipe up inside the ViewPager it doesn't collapse toolbar. Only when I try to swipe up inside the header itself.

How can I enable collapsing of toolbar when swiping inside the viewpager ?

Thanks

Answer 1

Try the following by including ViewPager inside NestedScrollView

<android.support.v4.widget.NestedScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true"
    app:layout_behavior="@string/appbar_scrolling_view_behavior">
  <android.support.v4.view.ViewPager
    android:id="@+id/view_pager_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"/>
</android.support.v4.widget.NestedScrollView>