Connect mysql to Android Studio

Question

I have a web-based system where his database is with Mysql. I’m starting now to develop the application on Android using Android Studio. I wonder if you have how to create Mysql connection in Android Studio, taking advantage of the tables of this system that are already ready and populated. I have seen some models using Sqlite, but it would not be my case. I tried with the code below, but when I run, it shows that the app stopped working:

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tela_login);

        editEmail = (EditText)findViewById(R.id.editEmail);
        editSenha = (EditText)findViewById(R.id.editSenha);
        btnAcessar = (Button)findViewById(R.id.btnAcessar);
        txtLembrarSenha = (TextView)findViewById(R.id.txtLembrarSenha);

       btnAcessar.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View view) {

               ConnectivityManager connectivityManager =
                       (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
               NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();

               if(networkInfo != null && networkInfo.isConnected()){

                   String email = editEmail.getText().toString();
                   String senha = editSenha.getText().toString();

                   if(email.isEmpty() || senha.isEmpty()){
                       Toast.makeText(getApplicationContext(),"Favor preencher corretamente os campos",Toast.LENGTH_LONG).show();
                   }else{
                       url = "http://192.168.0.13/projeto/conexao-mobile/logar.php";
                       parametros = "email=" + email + "&senha=" + senha;
                       new SolicitaDados().execute(url);
                   }

               }else {
                   Toast.makeText(getApplicationContext(), "Nenhuma conexão ativa", Toast.LENGTH_LONG).show();
               }
           }
       });
    }

    private class SolicitaDados extends AsyncTask<String, Void, String> {

       @Override
       protected String doInBackground(String... urls){

            return Conexao.postDados(urls[0], parametros);

       }

        @Override
        protected void onPostExecute(String resultado){
           // textView.setText(result);
            txtErro.setText(resultado);

        }
    }

The error that appears is:

01-21 17:20:21.947 16889-16889/br.com.projeto.acessosistema E/AndroidRuntime: FATAL EXCEPTION: main
Process: br.com.projeto.acessosistema, PID: 16889
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at br.com.projeto.acessosistema.TelaLogin$SolicitaDados.onPostExecute(TelaLogin.java:78)
at br.com.projeto.acessosistema.TelaLogin$SolicitaDados.onPostExecute(TelaLogin.java:66)
at android.os.AsyncTask.finish(AsyncTask.java:660)
at android.os.AsyncTask.-wrap1(AsyncTask.java)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:677)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6123)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757)

The Connection I’m using in a basic way:

<?php
$email = $_POST["Login"];
$senha = $_POST["Senha"];

$conexao = mysqli_connect('192.168.0.13','root','','projeto');

$sql = mysqli_query($conexao,"SELECT * FROM pe_acessos Email = '".$email."' AND SenhaAcessos = '".$senha."'");

if(mysqli_num_rows($sql) == 0){
   echo "Login ou senha inválidos";
}else{
 echo "Vamos conectar";
}
?>

The database as well as the tables exist.