ViewPager with WebViews that shows individual ProgressBars for each WebView when it's loading

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.loadingview.MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@android:color/holo_blue_bright" />

</RelativeLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.loadingview">

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

MainActivity.java

package com.example.loadingview;

import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ProgressBar;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

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

        final List<String> pages = new ArrayList<>();
        pages.add("https://google.com");
        pages.add("https://stackoverflow.com");

        final ViewPager viewPager = (ViewPager) findViewById(R.id.viewPager);
        viewPager.setAdapter(new CustomPagerAdapter(pages));
    }

    static class CustomPagerAdapter extends PagerAdapter {
        private final List<String> pages;

        CustomPagerAdapter(List<String> pages) {
            this.pages = pages;
        }

        @Override
        public int getCount() {
            return pages.size();
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            final View viewItem = LayoutInflater.from(container.getContext()).inflate(R.layout.view_pager_item, container, false);
            final WebView webView = (WebView) viewItem.findViewById(R.id.webView);
            webView.setVisibility(View.INVISIBLE);
            final ProgressBar progressBar = (ProgressBar) viewItem.findViewById(R.id.progressBar);
            progressBar.setVisibility(View.VISIBLE);
            webView.setWebViewClient(new WebViewClient() {
                @Override
                public void onPageFinished(WebView view, String url) {
                    progressBar.setVisibility(View.GONE);
                    webView.setVisibility(View.VISIBLE);
                }
            });
            webView.loadUrl(pages.get(position));
            container.addView(viewItem);
            return viewItem;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            container.removeView((View) object);
        }

        @Override
        public boolean isViewFromObject(View view, Object object) {
            return view == object;
        }
    }
}

view_pager_item.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <WebView
        android:id="@+id/webView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <ProgressBar
        android:id="@+id/progressBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center" />

</FrameLayout>