progress dialog in android

download: http://www.mediafire.com/download/ou7hmypj3iynwdc/ProgressDialogExample.tar.gz

package com.helloandroid.android.progressdialogexample;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.KeyEvent;
import android.widget.TextView;

public class ProgressDialogExample extends Activity implements Runnable {

private String pi_string;
private TextView tv;
private ProgressDialog pd;

@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);

tv = (TextView) this.findViewById(R.id.main);
tv.setText("Press any key to start calculation");
}

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {

pd = ProgressDialog.show(this, "Working..", "Calculating Pi", true,
false);

Thread thread = new Thread(this);
thread.start();

return super.onKeyDown(keyCode, event);
}

public void run() {
pi_string = Pi.computePi(800).toString();
handler.sendEmptyMessage(0);
}

private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
pd.dismiss();
tv.setText(pi_string);

}
};

}