MainActivity.java

package com.example.gourav.pdf;

import android.content.Context;
import android.content.DialogInterface;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.webkit.WebView;
import android.widget.ProgressBar;
import android.widget.Toast;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class MainActivity extends AppCompatActivity {
ProgressBar bar;
    String s;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DatabaseReference mref= FirebaseDatabase.getInstance().getReference();
        mref=mref.child("root").child("url");
        bar= (ProgressBar)findViewById(R.id.progressBar2);
        if(isNetworkAvailable())
        {
        mref.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                s=dataSnapshot.child("Coding").getValue().toString();
                WebView mWebView=new WebView(MainActivity.this);
                mWebView.getSettings().setJavaScriptEnabled(true);
                mWebView.loadUrl("https://docs.google.com/gview?embedded=true&url="+s);
                setContentView(mWebView);

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }
    else
        {
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setMessage("No Internet Connection").setPositiveButton("OK", new DialogInterface.OnClickListener() {
                @RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN)
                public void onClick(DialogInterface dialog, int id) {
                    finishAffinity();
                }
            }).show();
        }
    }
    private boolean isNetworkAvailable() {
        ConnectivityManager connectivityManager
                = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
        return activeNetworkInfo != null && activeNetworkInfo.isConnected();
    }
}