在x操作后显示插页式广告（在基于片段和内容的应用中）

Question

我知道如何展示插页式广告，但我需要帮助才能在x次操作后显示插页式广告，即点击3个片段后。这是一款非游戏应用（仅限内容），我使用片段，而非活动。目前我每隔60秒就会展示一次广告，但它会违反赞助政策并给用户留下不好的印象。我的代码如下：

    package com.xxx.xxxx;

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.FragmentTransaction;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

import com.google.android.gms.ads.AdListener;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.InterstitialAd;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;



public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    NavigationView navigationView = null;
    Toolbar toolbar = null;
    InterstitialAd mInterstitialAd;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        // Prepare the Interstitial Ad
        mInterstitialAd = new InterstitialAd(MainActivity.this);

        // Insert the Ad Unit ID
        mInterstitialAd.setAdUnitId(getString(R.string.interstitial_ads));
        // mInterstitialAd.loadAd(adRequest);

        mInterstitialAd.setAdListener(new AdListener() {
            public void onAdLoaded() {
                // don't show Ad here
            }

            @Override
            public void onAdClosed() {
                createRequest(); //load request whenever ad closed by user
            }
        });

        ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
        scheduler.scheduleAtFixedRate(new Runnable() {
            public void run() {

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        if (mInterstitialAd.isLoaded())
                            mInterstitialAd.show();
                        else
                            createRequest();
                    }
                });
            }
        }, 60, 60, TimeUnit.SECONDS);


        //Set fragment initially
        MainFragment fragment = new MainFragment();
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_container, fragment);
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();

        toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);



        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        navigationView = findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
    }

    public void createRequest() {

        AdRequest adRequest = new AdRequest.Builder().build();
        mInterstitialAd.loadAd(adRequest);
    }


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

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();


        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);


        return true;
    }
}