android对话框的使用

package com.test;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SubMenu;
import android.view.View;
import android.view.ContextMenu.ContextMenuInfo;
import android.widget.TextView;
import android.widget.Toast;
public class layoutMain extends Activity { 
 public void onCreate(Bundle savedInstanceState) {  
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
 } 
 public boolean onCreateOptionsMenu(Menu menu) {
  MenuItem menuItem = menu.add(0, 0, 0, "菜单");  
  menuItem.setIcon(R.drawable.icon01);  
  menuItem.setAlphabeticShortcut('a');   
        menu.add(0, 1, 1, "退出").setIcon(R.drawable.icon02);
  menu.add(0, 2, 2, "菜单3").setIcon(R.drawable.icon03);   
  menu.add(0, 4, 4, "菜单7").setIcon(R.drawable.icon04);
  menu.add(0, 3, 3, "菜单8").setIcon(R.drawable.icon05);     
  return super.onCreateOptionsMenu(menu);
 }

 public boolean onOptionsItemSelected(MenuItem item) {  
 // Toast.makeText(layoutMain.this, "被单击的菜单项为：" + String.valueOf(item.getItemId()), Toast.LENGTH_SHORT).show();
     
  switch(item.getItemId()){
          case 1:
        openOptionsDialog();
        break;
       }  
  return super.onOptionsItemSelected(item);
 } 
 private void openOptionsDialog(){         //这种编码方式很好的  
       new AlertDialog.Builder(this)
      .setTitle("标题")
      .setMessage("真的要离开吗？")
      .setNegativeButton("离开", new DialogInterface.OnClickListener(){
        public void onClick(DialogInterface dialog, int which) { 
             finish();
         }       
      })
      .setPositiveButton("不离开", new DialogInterface.OnClickListener(){
          public void onClick(DialogInterface dialog, int which) {
     
          }       
      }).show();
 }  
}