ScrollingActivity.java

package com.kmshack.topscrollsample;

import android.content.Intent;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.provider.Settings;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.widget.NestedScrollView;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;

import com.kmshack.topscroll.TopScrollHelper;

public class ScrollingActivity extends AppCompatActivity {

    private NestedScrollView mNestedScrollView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scrolling);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        mNestedScrollView = (NestedScrollView) findViewById(R.id.scrollView);

        initTopScrollHelper();
    }

    public static int OVERLAY_PERMISSION_REQ_CODE = 1234;

    public void initTopScrollHelper() {
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (!Settings.canDrawOverlays(this)) {
                Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                        Uri.parse("package:" + getPackageName()));
                startActivityForResult(intent, OVERLAY_PERMISSION_REQ_CODE);
                return;
            }
        }

        TopScrollHelper.getInstance(getApplicationContext()).addTargetScrollView(mNestedScrollView);

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (requestCode == OVERLAY_PERMISSION_REQ_CODE) {
                if (!Settings.canDrawOverlays(this)) {
                    TopScrollHelper.getInstance(getApplicationContext()).addTargetScrollView(mNestedScrollView);
                }
            }
        }
    }

    @Override
    protected void onDestroy() {
        TopScrollHelper.getInstance(getApplicationContext()).removeTargetScrollView(mNestedScrollView);
        super.onDestroy();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_scrolling, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}