@JavascriptInterface and RewardedVideoAd Android Admob

There is an Android mechanism that allows you to run Android function from javascript:

      <input class="button" type="button" value="FREE life" onclick="startRewardVideo('some parameters can be passed to Android from here')">
            <script type="text/javascript">
                function startRewardVideo(paramFromJS) {
                    Android.startRewardVideoAndroidFunction(paramFromJS);
                }
            </script>

now you need class that knows what to do with your javascript:

package fr.bbbb.myapplication;

import android.content.Context;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.webkit.JavascriptInterface;

import android.webkit.WebChromeClient;

import android.webkit.WebView;

import android.webkit.WebViewClient;

import android.webkit.WebSettings;

import android.widget.Toast;

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

import com.google.android.gms.ads.MobileAds;

import com.google.android.gms.ads.reward.RewardItem;

import com.google.android.gms.ads.reward.RewardedVideoAd;

import com.google.android.gms.ads.reward.RewardedVideoAdListener;

public class MainActivity extends AppCompatActivity implements RewardedVideoAdListener{

    private WebView webView;

    private RewardedVideoAd mRewardedVideoAd;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        webView = (WebView) findViewById(R.id.webview);

        webView.setWebViewClient(new WebViewClient());

        WebSettings settings = webView.getSettings();

        settings.setJavaScriptEnabled(true);

        webView.setWebChromeClient(new WebChromeClient());

        MobileAds.initialize(this, "ca-app-pub-3940256099942544~3347511713");

        mRewardedVideoAd = MobileAds.getRewardedVideoAdInstance(this);

        mRewardedVideoAd.setRewardedVideoAdListener(this);

        webView.addJavascriptInterface(new MyJavascriptInterface(this) , "Android");

        webView.loadUrl("http://www.bbbb.fr");

        mRewardedVideoAd.loadAd("ca-app-pub-3940256099942544/5224354917", new AdRequest.Builder().build());

    }

  public class MyJavascriptInterface {

        private Context context;

        public MyJavascriptInterface(Context context){

            this.context = context;

        }

        @JavascriptInterface

        public void startRewardVideoAndroidFunction(){

            runOnUiThread(new Runnable() {

                public void run() {

                    if (mRewardedVideoAd.isLoaded()) {

                        mRewardedVideoAd.show();

                    }

                }

            });

        }

    }

    private void loadRewardedVideoAd() {

        mRewardedVideoAd.loadAd("ca-app-pub-8182467776458634/7199599910", new AdRequest.Builder().build());

    }

    @Override

    public void onRewardedVideoAdLeftApplication() {

        Toast.makeText(this, "onRewardedVideoAdLeftApplication",Toast.LENGTH_SHORT).show();

    }

    @Override

    public void onRewardedVideoAdClosed() {

        Toast.makeText(this, "onRewardedVideoAdClosed", Toast.LENGTH_SHORT).show();

    }

    @Override

    public void onRewardedVideoAdFailedToLoad(int errorCode) {

        Toast.makeText(this, "onRewardedVideoAdFailedToLoad", Toast.LENGTH_SHORT).show();

    }

    @Override

    public void onRewardedVideoAdLoaded() {

        Toast.makeText(this, "onRewardedVideoAdLoaded", Toast.LENGTH_SHORT).show();

    }

    @Override

    public void onRewardedVideoAdOpened() {

        Toast.makeText(this, "onRewardedVideoAdOpened", Toast.LENGTH_SHORT).show();

    }

    @Override

    public void onRewardedVideoStarted() {

        Toast.makeText(this, "onRewardedVideoStarted", Toast.LENGTH_SHORT).show();

    }

    @Override

    public void onRewardedVideoCompleted() {

        Toast.makeText(this, "onRewardedVideoCompleted", Toast.LENGTH_SHORT).show();

    }

    @Override

    public void onRewarded(RewardItem rewardItem) {

    loadRewardedVideoAd();

    }

}

Here you have full tutorial:

https://stackoverflow.com/questions/48403912/webview-remote-site-and-reward-videos?rq=1

https://openclassrooms.com/forum/sujet/rewarded-video-sur-une-application-webview?page=1