Menu和AlertDialog对话框
要在一个activity中实现菜单必须重写两个方法：
1. onCreateOptionsMenu()用于创建菜单
2. onOptionsItemSelected() 用于处理点击菜单选项事件
实例代码：

package com.kevin.dialog;import android.app.Activity;import android.app.AlertDialog;import android.content.DialogInterface;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;public class Main extends Activity {private static final int HELPGROUP = 0;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);    }    private void openOptionsDialog(){    AlertDialog.Builder builder = new AlertDialog.Builder(this);    // 设置标题    builder.setTitle(R.string.about);    // 设置对话框信息    builder.setMessage(R.string.message);        // 添加确定按钮    builder.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {    // 点击确定单击事件处理    @Overridepublic void onClick(DialogInterface dialog, int which) {System.out.println("确定按钮被点击.");}});     // 添加取消按钮    builder.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {System.out.println("取消按钮被点击.");}});    // 显示对话框    builder.show();    }    // 要实现菜单必须实现以下两个函数(onCreateOptionsMenu和onOptionsItemSelected)// 创建菜单    @Overridepublic boolean onCreateOptionsMenu(Menu menu) {menu.add(HELPGROUP, 0, 0, R.string.about);menu.add(HELPGROUP, 1, 1, R.string.close);return super.onCreateOptionsMenu(menu);}    // 选择item并相应@Overridepublic boolean onOptionsItemSelected(MenuItem item) {switch (item.getItemId()) {// 关于选项case 0:openOptionsDialog();break;// 关闭选项case 1:finish();break;default:break;}return super.onOptionsItemSelected(item);}}