How do I make a Scrollable TextView inside CollapsingToolbar?

Question

I am currently experimenting with CoordinatorLayout + AppbarLayout + CollapsingToolbarLayout in a way such that:

1) Scroll down the Appbar using "Toolbar" [ No Nested ScrollView / RecyclerView ].

2) The content below the appbar should move along with the appbar scrolling.

3) Multiple images kept under ViewPager.

4) The last item in the ViewPager would be an textview.

I have achieved 1) and 2) using the following 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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:tools="http://schemas.android.com/tools">

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

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/flexible.example.collapsing"
            android:layout_width="match_parent"
            android:layout_height="300dp"
            app:expandedTitleMarginBottom="94dp"
            app:layout_scrollFlags="scroll|exitUntilCollapsed|snap"
            app:contentScrim="?colorPrimary"
            >

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_margin="10dp"
                android:id="@+id/text_sample"
                android:scrollbars="vertical"
                android:scrollIndicators="right"
                app:layout_collapseMode="parallax"
                app:layout_scrollFlags="scroll|enterAlways"
                android:layout_gravity="center"
                android:nestedScrollingEnabled="true"
                />
        </android.support.design.widget.CollapsingToolbarLayout>

        <android.support.v7.widget.Toolbar
            android:id="@+id/ioexample.toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/PM01"
            android:elevation="4dp"
            app:layout_collapseMode="pin"
            app:layout_anchor="@id/flexible.example.collapsing"
            app:layout_anchorGravity="bottom"
            app:theme="@style/ThemeOverlay.AppCompat.Light"
            style="@style/ToolBarWithNavigationBack"
            app:layout_scrollFlags="scroll|enterAlways|snap"
            >

        </android.support.v7.widget.Toolbar>


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

    <android.support.v7.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/recyclerviewcontainer"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

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

What I am trying to achieve now is to make the textview inside collpasingtoolbarlayout is to be scrollable (#4 above). Since my search till now has made me believe that the Appbar is handling all the touch events by itself, this doesn't seems to be easy. But since it is a requirement, I would be more than happy to have a guidance / pointers to help me complete this.

Can someone please let me know what and where to look for achieving this functionality.

Answer 1

After a lot of research and some more searching through SO, I got an idea what I need to do in order to achieve the desired effect:

1) Implement a custom behavior for appbarlayout :

public class AppBarLayoutCustomBehavior extends AppBarLayout.Behavior {
    private boolean setIntercept = false;
    private boolean lockAppBar = false;

    DragCallback mDragCallback = new DragCallback() {
        @Override
        public boolean canDrag(@NonNull AppBarLayout appBarLayout) {
            return !lockAppBar;
        }
    };

    @Override
    public boolean onInterceptTouchEvent(CoordinatorLayout parent, AppBarLayout child, MotionEvent ev) {
        super.onInterceptTouchEvent(parent, child, ev);
        return setIntercept;
    }

    public void setInterceptTouchEvent(boolean set) {
        setIntercept = set;
    }

    public AppBarLayoutCustomBehavior() {
        super();
        setDragCallback(mDragCallback);
    }

    public AppBarLayoutCustomBehavior(Context ctx, AttributeSet attributeSet) {
        super(ctx, attributeSet);
        setDragCallback(mDragCallback);
    }

    public void lockAppBar() {
        lockAppBar = true;
    }

    public void unlockAppBar() {
        lockAppBar = false;
    }
}

2) Use this custom behavior with app bar :

CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams)appBarLayout.getLayoutParams();
        final AppBarLayoutCustomBehavior mBehavior = new AppBarLayoutCustomBehavior();
        lp.setBehavior(mBehavior);

/// use toolbar to enable/disable dragging on the appbar behavior. This way
/// out toolbar acts as a drag handle for the app bar.
        Toolbar toolbar = (Toolbar) activity.findViewById(R.id.main_toolbar);
        toolbar.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch(event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        mBehavior.setInterceptTouchEvent(true);
                        return true;
                    case MotionEvent.ACTION_CANCEL:
                        mBehavior.setInterceptTouchEvent(false);
                        return true;
                }
                return false;
            }
        });

3) Set movement method on the textview to make it scrollable

textView.setMovementMethod(ScrollingMovementMethod.getInstance());