Android AlertDialog

package com.example.myact4;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
/**
* AlertDialog练习
* @author shaobn
*
*/
public class MainActivity extends ActionBarActivity {
private Button button;
private TextView tView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) this.findViewById(R.id.button1);
tView = (TextView) this.findViewById(R.id.textView1);
final Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
// TODO Auto-generated method stub
super.handleMessage(msg);
int num = msg.arg1;
MainActivity.this.tView.setText(String.valueOf(num));
Toast.makeText(MainActivity.this, Thread.currentThread().getName(), Toast.LENGTH_LONG).show();
}
};
button.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
builder.setIcon(R.drawable.ic_launcher);
builder.setTitle("友情提示");
builder.setMessage("您确定要删除吗？");
builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {

@Override
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub
arg0.cancel();
}
});
builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {

@Override
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub
Runnable runnable=new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
Message message = new Message();
message.arg1 = 3;
handler.sendMessage(message);

}
};
new Thread(runnable).start();
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
}
});

}
}