public class MainActivity extends AppCompatActivity implements View.OnClickListener {

private EditText etUsername,etEmail,etPassword;
private Button bt;
private ProgressDialog progressDialog;

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

    etEmail=(EditText)findViewById(R.id.et_email);
    etUsername=(EditText)findViewById(R.id.et_username);
    etPassword=(EditText)findViewById(R.id.et_pasword);

    bt=(Button)findViewById(R.id.bt);

    progressDialog =new ProgressDialog(this);

    bt.setOnClickListener(this);

}


private void registerUser(){
        final String email=etEmail.getText().toString().trim();
        final String username=etUsername.getText().toString().trim();
        final String password=etPassword.getText().toString().trim();

    progressDialog.setMessage("Registering..");
    progressDialog.show();
    StringRequest stringRequest = new StringRequest(Request.Method.POST,
            Constants.URL_REGISTER,
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    progressDialog.dismiss();

                    try {
                        JSONObject jsonObject = new JSONObject(response);
                        Toast.makeText(getApplicationContext(),jsonObject.getString("message"),Toast.LENGTH_LONG).show();
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    progressDialog.hide();
                    Toast.makeText(getApplicationContext(),error.getMessage(),Toast.LENGTH_LONG).show();
                }
            }){
        @Override
        protected Map<String, String> getParams() throws AuthFailureError {
            Map<String,String> params=new HashMap<>();
            params.put("username",username);
            params.put("email",email);
            params.put("password",password);

            return params;
        }
    };

    RequestQueue requestQueue = Volley.newRequestQueue(this);
    requestQueue.add(stringRequest);

}

@Override
public void onClick(View v) {
    if (v==bt)
        registerUser();
}