Help for Progress Bar

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity"
    android:orientation="vertical"
    >

  <ProgressBar
      style="?android:attr/progressBarStyleLarge"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/progressBar"
      android:layout_centerVertical="true"
      android:layout_centerHorizontal="true"
      android:indeterminate="false"
      android:layout_gravity="center"
      />

  <RelativeLayout
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:id="@+id/container"
      >

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/password"
        android:layout_below="@+id/email"
        android:layout_centerHorizontal="true"
        android:hint="Password"
        android:layout_margin="10dp"
        />

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/username"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:hint="UserName / Restaurant Name"
        android:layout_margin="10dp"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Existing User? Please Login here->"
        android:id="@+id/login"
        android:layout_below="@+id/submit"
        android:layout_centerHorizontal="true"
        android:layout_margin="10dp"
        />

    <Button
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Submit Registration"
        android:id="@+id/submit"
        android:layout_below="@+id/password"
        android:layout_centerHorizontal="true"
        android:layout_margin="10dp"
        />

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/email"
        android:layout_below="@+id/username"
        android:layout_centerHorizontal="true"
        android:hint="Email "
        android:layout_margin="10dp"
        />
  </RelativeLayout>
</RelativeLayout>

MainActivity.java

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.RelativeLayout;
import android.widget.TextView;
import org.json.JSONException;
import org.json.JSONObject;

public class MainActivity extends AppCompatActivity {

  ProgressBar progressBar;
  RelativeLayout container;

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

    progressBar = (ProgressBar) findViewById(R.id.progressBar);
    progressBar.setVisibility(View.GONE);
    container = (RelativeLayout) findViewById(R.id.container);

    final EditText username = (EditText) findViewById(R.id.username);
    final EditText email = (EditText) findViewById(R.id.email);
    final EditText password = (EditText) findViewById(R.id.password);

    final Button submit = (Button) findViewById(R.id.submit);
    submit.setOnClickListener(new View.OnClickListener() {
      @Override public void onClick(View view) {

        progressBar.setVisibility(View.VISIBLE);
        container.setVisibility(View.GONE);

        final String get_username = username.getText().toString();
        final String get_email = email.getText().toString();
        final String get_password = password.getText().toString();

        Response.Listener<String> response_listener = new Response.Listener<String>() {
          @Override public void onResponse(String response) {
            try {
              JSONObject jsonObject = new JSONObject(response);
              boolean result = jsonObject.getBoolean("register_result");
              progressBar.setVisibility(View.GONE);
              container.setVisibility(View.VISIBLE);

              if (result) {

                AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);

                builder.setMessage("Registration Done!")
                    .setNegativeButton("Back", null)
                    .create()
                    .show();
              } else {

                AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                builder.setMessage("User already existed! Please try different Email")
                    .setNegativeButton("Back", null)
                    .create()
                    .show();
              }
            } catch (JSONException e) {
              e.printStackTrace();
            }
          }
        };
        RegisterRequest register_request =
            new RegisterRequest(get_username, get_email, get_password, response_listener);
        RequestQueue queue = Volley.newRequestQueue(MainActivity.this);
        queue.add(register_request);
      }
    });

    TextView register = (TextView) findViewById(R.id.login);
    register.setOnClickListener(new View.OnClickListener() {
      @Override public void onClick(View view) {
        Intent intent = new Intent(MainActivity.this, LoginActivity.class);
        MainActivity.this.startActivity(intent);
      }
    });
  }