Activity 在預設的情況中按下選單鍵是沒有反應的, 要讓選單鍵產生作用相當簡單,只要注意以下兩點
1. 複寫 activity的 onCreateOptionsMenu 方法, 在方法中加入想要顯示的選單項目(MenuItem)
2. 複寫 activity的 onOptionsItemSelected 方法, 在方法中加入點選各選單項目(MenuItem)要對應的動作
實作程式碼如下

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends Activity
{
    public static final int ADD_ID = 0;
    public static final int DELETE_ID = 1;
    public static final int ABOUT_ID = 2;
    public static final int EXIT_ID = 3;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        super.onCreateOptionsMenu(menu);
        addMenuItems(menu);
        return true;
    }
    private void addMenuItems(Menu menu)
    {
        menu.add(Menu.NONE, ADD_ID, Menu.NONE, R.string.menu_add);
        menu.add(Menu.NONE, DELETE_ID, Menu.NONE, R.string.menu_delete);
        menu.add(Menu.NONE, ABOUT_ID, Menu.NONE, R.string.menu_about);
        menu.add(Menu.NONE, EXIT_ID, Menu.NONE, R.string.menu_exit);
    }
    public boolean onOptionsItemSelected(MenuItem item)
    {
        selectMenuItemEvents(item);
        return super.onOptionsItemSelected(item);
    }
    private void selectMenuItemEvents(MenuItem item)
    {
        switch (item.getItemId()) {
            case ADD_ID:
                setTitle(getResources().getString(R.string.menu_add));
                break;
            case DELETE_ID:
                setTitle(getResources().getString(R.string.menu_delete));
                break;
            case ABOUT_ID:
                setTitle(getResources().getString(R.string.menu_about));
                break;
            case EXIT_ID:
                break;
        }
    }
}

 
main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
</LinearLayout>

 
strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name">MENU</string>
    <string name="menu_add">add item</string>
    <string name="menu_delete">delete item</string>
    <string name="menu_about">about</string>
    <string name="menu_exit">exit</string>
    <string name="menu_about_msg">message for about...</string>
    <string name="str_ok">OK</string>
    <string name="str_cancel">Cancel</string>
    <string name="menu_exit_msg">exit system？</string>
</resources>