CollapsingToolbarLayout with a ViewPager

Question

I'm trying to use the CollapsingToolbarLayout to have a collapsible toolbar with a ViewPager that fades away while scrolling up but I seem to lose the ability to scroll up if the ViewPager is present.

The ViewPager is supposed to show multiple images in the Toolbar.

Here's the XML:

<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

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

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsing_toolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:contentScrim="?attr/colorPrimary"
            android:fitsSystemWindows="true">

            <android.support.v4.view.ViewPager
                android:id="@+id/pager"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:layout_collapseMode="parallax"
                android:fitsSystemWindows="true">
            </android.support.v4.view.ViewPager>

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

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

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

    <android.support.v4.widget.NestedScrollView
        android:id="@+id/scroll"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <!-- Content -->

    </android.support.v4.widget.NestedScrollView>

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

Answer 1

I managed to fix this by setting the ViewPager's height to a fixed size. It seems that wrap_content doesn't regardless of the image size.