Priority in progressdialog

Diego, I see some strange things in your code, for example, you're calling the AlertDialog alertDialog = new AlertDialog.Builder(context).create(); method inside the loop ( while ). Second, you are running a process that may take a while inside the main Thread.

You could use AsyncTask , so in onPreExecute method, you start ProgressDialog , in method doInBackground you make your Http call and onPostExecute method, you finalize your ProgressDialog and it displays its AlertDialog .

Read more about AsyncTask

The right thing to do is to use an AsyncTask

-Your activity would look like this:

public class DemE extends Activity implements View.OnClickListener
{
    //Suponho que seja aqui aonde você roda o metodo
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        findViewById(R.id.btnConDe).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        String nomeProduto =  findViewById(R.id.cmdDigDe).getText().toString();
        String laboratorio = null;
        String aliquota = "17";


        if (nomeProduto == "") 
            Toast.makeText(DemE.this, "Por favor digite o nome do medicamento", Toast.LENGTH_LONG).show();
        else
            new BuscaMedicamentosAsync(this).execute(
                new StringBuilder("nome=")
                        .append(nomeProduto)
                        .append("&aliquota=")
                        .append(aliquota)
                        .append("&laboratorio=")
                        .append(laboratorio == null? "" : laboratorio));
    }
}

-E processing is by async:

public final class BuscaMedicamentosAsync extends AsyncTask<CharSequence, Integer, CharSequence>
{
    private final AlertDialog alertDialog;
    private final ProgressDialog progressDialog;

    public BuscaMedicamentosAsync(Context contexto)
    {
        this.alertDialog = new AlertDialog.Builder(contexto).create();
        alertDialog.setTitle("Medicamentos:");
        alertDialog.setButton(0, "Voltar", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.cancel();
            }
        });

        progressDialog = new ProgressDialog(contexto);
        progressDialog.setTitle("Listando medicamentos");
        progressDialog.setMessage("Buscando...");
        progressDialog.show();
        progressDialog.setCancelable(false); //Impedir que o usuario feche o dialogo
    }

    @Override
    protected CharSequence doInBackground(CharSequence... parametros)
    {
        StringBuilder result = new StringBuilder();
        try {
            URL url = new URL("http");
            URLConnection con = url.openConnection();
            con.setDoOutput(true);
            OutputStreamWriter writer = new OutputStreamWriter(con.getOutputStream());

            writer.write(parametros[0].toString());
            writer.flush();

            BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream()));
            String line;


            while ((line = reader.readLine()) != null) {

                result.append(line);
            }

            writer.close();
            reader.close();

        } catch (Exception e) {
            //Trata a exceção
        }

        return Html.fromHtml(result.toString()).toString();
    }

    @Override
    protected void onPostExecute(CharSequence text) {
        super.onPostExecute(text);

        progressDialog.dismiss();

        alertDialog.setMessage(text);
        alertDialog.show();
    }
}

Recommended reading

• AsyncTask