application crashes due to adding data to the database

i'm beginner android developer. But i have problem add data from android studio to phpmyadmin. I found a ready code, but for some reason when i click on the button, the application crashes. i think the problem is with "NetworkCalls".<IF I DELETE IT THEN THE APP DOESN'T CRASH BUT DOESN'T PERFORM THE FUNCTION.

Activity:

<?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="match_parent"
    android:layout_height="match_parent"
    tools:context="com.test.test.ScreenOne">

    <EditText
        android:id="@+id/etUsername"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Name"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="330dp"/>

    <EditText
        android:id="@+id/etPassword"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPassword"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="400dp"/>

    <Button
        android:id="@+id/bSave"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="save"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="600dp"
        android:onClick="saveb"/>
</RelativeLayout>

MainCode:

package com.test.test;

import android.app.ProgressDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;

import java.util.HashMap;
import java.util.Map;

public class ScreenOne extends AppCompatActivity {

    private static final String URL_SAVE = "http://IP/save.php";
    private EditText username;
    private EditText password;
    Button save;
    String name;
    String pass;

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

        username = (EditText) findViewById(R.id.etUsername);
        password = (EditText) findViewById(R.id.etPassword);

        save = (Button) findViewById(R.id.bSave);
    }

    public void saveb(View view) {
        saveRequest();

    }

    private void saveRequest() {
        name = username.getText().toString().trim();
        pass = password.getText().toString().trim();
        final ProgressDialog mDialog = new ProgressDialog(this);
        mDialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        mDialog.setMessage("Loading...");
        mDialog.show();



        StringRequest request = new StringRequest(Request.Method.POST, URL_SAVE,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        mDialog.dismiss();
                        Toast.makeText(ScreenOne.this, response, Toast.LENGTH_LONG).show();
                        username.setText("");
                        password.setText("");
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        mDialog.dismiss();
                        Toast.makeText(ScreenOne.this, "Something went wrong", Toast.LENGTH_LONG).show();
                    }
                }) {
            @Override
            protected Map<String, String> getParams() throws AuthFailureError {
                Map<String, String> key = new HashMap<>();
                key.put("username", name);
                key.put("password", pass);
                return key;
            }
        };

        NetworkCalls.getInstance().addToRequestQueue(request);
    }


}

NetworkCalls:

    package com.test.test;
    
    import android.content.Context;
    
    import com.android.volley.Request;
    import com.android.volley.RequestQueue;
    import com.android.volley.toolbox.Volley;
    
    public class NetworkCalls {
        private RequestQueue requestQueue;
        private static Context context;
    
        private static NetworkCalls ourInstance = new NetworkCalls();
    
        public static NetworkCalls getInstance() {
            return ourInstance;
        }
    
        private NetworkCalls() {
        }
    
        public RequestQueue getRequestQueue(){
            requestQueue = Volley.newRequestQueue(context.getApplicationContext());
            return requestQueue;
        }
    
        public <T> void addToRequestQueue(Request<T> request){
            getRequestQueue().add(request);
        }
    }

Your main problem is to pass context When the network is called NetworkCalls class got null context. so your app crushed. So change your network class like below.

Change your Network class like this:

public class NetworkCalls {
    private static NetworkCalls instance;
    private RequestQueue requestQueue;
    private static Context mContext;
        
    private NetworkCalls(Context context){
        mContext = context;
        requestQueue = getRequestQueue();
    }

    public static synchronized NetworkCalls getInstance(Context context){
        if(instance == null){
            instance = new NetworkCalls(context);
        }
        return instance;
    }
    
    public RequestQueue getRequestQueue(){
        requestQueue = Volley.newRequestQueue(mContext.getApplicationContext());
        return requestQueue;
    }
    
    public <T> void addToRequestQueue(Request<T> request){
        getRequestQueue().add(request);
    }
}

And from MainActivity saveRequest() method change this line NetworkCalls.getInstance().addToRequestQueue(request); to NetworkCalls.getInstance(getApplicationContext()).addToRequestQueue(request);

Happy Coding!