Android :: Alert Dialog Not Appearing In Android

public class BabyName extends Activity implements View.OnClickListener, Runnable{
/** Called when the activity is first created. */
Login loginclass=new Login();
ProgressDialog dialog;

Thread t=new Thread(this, "sample");

AlertDialog al;
long id;
boolean flg=false;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);...........................