Can't scroll completely down in ViewPager with NestedScrollView in CollapsedToolBarLayout

Question

I'm creating a fragment with a collapsing Toolbar Layout using a ViewPager. This is the XML for the Layout:

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/htab_maincontent"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".activities.AppActivity">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/htab_appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:fitsSystemWindows="true"
        android:backgroundTint="@color/completeWhite">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/htab_collapse_toolbar"
            android:layout_width="match_parent"
            android:layout_height="420dp"
            android:fitsSystemWindows="true"
            app:contentScrim="@color/completeWhite"
            app:layout_scrollFlags="scroll|exitUntilCollapsed|snap"
            app:titleEnabled="false">

            <RelativeLayout
                android:id="@+id/brand_page"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:layout_collapseMode="parallax"
                android:paddingTop="24dp"
                android:layout_marginTop="?attr/actionBarSize">

                //Lots of images and texts that are collapsed

            </RelativeLayout>

            <android.support.v7.widget.Toolbar
                android:id="@+id/htab_toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:layout_gravity="top"
                android:layout_marginBottom="75dp"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

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

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

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

    <io.brandie.brandie.custom.NoSwipeViewPager
        android:id="@+id/htab_viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        android:layout_marginBottom="@dimen/spacing_giant"
        android:background="@color/white"/>

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

The viewPager is filled with fragments that use a gridview to display different cards, this is the xml for the Fragment of the first tab:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.NestedScrollView
    android:id="@+id/NestedScroll"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:fillViewport="true"
    android:fitsSystemWindows="true"
    android:layout_gravity="fill_vertical"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/all_campaigns_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="io.brandie.brandie.fragments.AllCampaignsFragment">

        <GridView xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/all_campaigns_grid"
            android:descendantFocusability="blocksDescendants"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:numColumns="2"
            android:verticalSpacing="10dp"
            android:horizontalSpacing="10dp"
            android:stretchMode="columnWidth"
            android:gravity="center" />

    </FrameLayout>

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

With this I can scroll down anywhere on the screen to make the toolbar collapse and the view-pager expand. The problem is, when the tool-bar is completely collapsed and only the tabs are showing, I can't scroll the viewPager anymore. Since it holds a gridView with a lot of items, it results in that I can't scroll through them all, since the scroll just "stops".

I want it to look like this

But instead, when the toolbar is collapsed, I can't scroll the viewPager down anymore. I can however scroll it up to reveal the toolbar again, that works without issues. I am using Android API 16, is that an issue?

How do I fix this very irritating problem?

EDIT: If I remove the NestedScrollView from the fragment XML, the collapsed Toolbar only collapses if I scroll on the toolbar. If I scroll the ViewPager, I can scroll through all content correctly, but the toolbar doesn't collapse.

Answer 1

Answer for your EDIT: Try using setNestedScrollingEnabled(false) on your GridView