Show/Hide view on up/down scroll in android - Using ScrollView

activity_scroll.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/white"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/parallax_image"
        android:layout_width="match_parent"
        android:layout_height="280dp"
        android:scaleType="centerCrop"
        android:src="@drawable/img_user_avatar" />

    <ScrollView
        android:id="@+id/scrollView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        android:orientation="vertical">

        <TextView
            android:id="@+id/tv_perhour"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="280dp"
            android:layout_weight="1"
            android:background="@color/white"
            android:gravity="left"
            android:text="@string/lorem_ipsum"
            android:textColor="@color/black"
            android:textSize="@dimen/size_large" />

    </ScrollView>

    <TextView
        android:id="@+id/tv_heading"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/white"
        android:gravity="left|center_vertical"
        android:paddingLeft="16dp"
        android:text="Hey there"
        android:textColor="@color/black"
        android:textSize="@dimen/size_large" />

</RelativeLayout>

HideShowScrollParallaxActivity.java

/**
 * Created by Saurabh(aqua) in 2017.
 */

public class ScrollActivity extends BaseActivity {

    /* view binding */
    @BindView(R.id.scrollView)ScrollView scrollView;
    @BindView(R.id.parallax_image)ImageView parallaxImage;
    @BindView(R.id.tv_perhour)TextView textView;
    @BindView(R.id.tv_heading)TextView heading;
    /* color binding */
    @BindColor(R.color.white)int whiteColor;
    @BindColor(android.R.color.transparent)int transparentColor;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        /* intially hide the view */
        heading.setAlpha(0f);
        /* set the scroll change listener on scrollview */
        scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
            @Override
            public void onScrollChanged() {
                /* get the maximum height which we have scroll before performing any action */
                int maxDistance = parallaxImage.getHeight();
                /* how much we have scrolled */
                int movement = scrollView.getScrollY();
                /*finally calculate the alpha factor and set on the view */
                float alphaFactor = ((movement * 1.0f) / (maxDistance - heading.getHeight()));
                if (movement >= 0 && movement <= maxDistance) {
                    /*for image parallax with scroll */
                    parallaxImage.setTranslationY(-movement/2);
                    /* set visibility */
                    heading.setAlpha(alphaFactor);
                }
            }
        });
    }

    /* can be replaced with setContentView() in onCreate() */
    /* kept for brevity */
    @Override
    protected int getActivityLayout() {
        return R.layout.ac_parallax;
    }
}

github?