import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends AppCompatActivity {

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

    public void calcular(View view) {

        EditText tdolar = (EditText) findViewById(R.id.dolar);
        String sdolar = tdolar.getEditableText().toString();
        double ddolar = Double.parseDouble(sdolar);

        EditText treal = (EditText) findViewById(R.id.real);
        String sreal  = treal.getEditableText().toString();
        double dreal = Double.parseDouble(sreal);

    double resultado = dreal/ddolar;
    TextView tresult = (TextView) findViewById(R.id.resultado);
    tresult.setText("$ " +String.format("%.2f",resultado));

    Toast.makeText(this,"$ " +String.format("%.2f",resultado),
            Toast.LENGTH_LONG).show();

        AlertDialog.Builder alerta = new AlertDialog.Builder(this);
        alerta.setTitle("Resultado");
        alerta.setMessage("$ " +String.format("%.2f",resultado));
        alerta.show();
    }
}