<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <group android:id="@+id/group1" android:checkableBehavior="single">
        <item
            android:id="@+id/action_settings"
            android:checkable="true"
            android:orderInCategory="100"
            android:showAsAction="never"
            android:title="@string/app_name"/>
        <item
            android:id="@+id/item1"
            android:alphabeticShortcut="B"
            android:orderInCategory="200"
            android:title="返回">
        </item>
        <item
            android:id="@+id/item2"
            android:title="背景颜色">
        </item>
    </group>
    <item android:id="@+id/item1"
          android:showAsAction="always"
          android:title="新游戏">
    </item>
    <item android:id="@+id/item2"
          android:showAsAction="always"
          android:title="帮助">
    </item>
    <item android:id="@+id/item3"
          android:showAsAction="always"
          android:actionLayout="@layout/clock"
          android:title="时钟">
    </item>

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

    <AnalogClock
        android:id="@+id/analogClock1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>
package com.example.sukodu;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
    public class Help extends Activity {

        private static final String MainActivity = null;
        private MenuInflater inflater;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // TODO Auto-generated method stub
            MenuInflater inflater = new MenuInflater(this);
            inflater.inflate(R.menu.main, menu);
            return super.onCreateOptionsMenu(menu);
        }
        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
            // TODO Auto-generated method stub
            switch (item.getItemId()) {
            case android.R.id.home:
                //创建启动MainActivity的Intent
                Intent intent=new Intent(this,MainActivity.class);
                //添加额外的Flag，将Activity栈中处于MainActivity之上的Activity弹出
                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(intent);
                break;
             case R.id.item1:
                Intent intent1=new Intent(this,Help.class);
                startActivity(intent1);
                break;
            default:
                break;
            }
            return super.onOptionsItemSelected(item);
        }
    }

    ActionBar actionBar = getActionBar();
        actionBar.setDisplayShowHomeEnabled(true);
        actionBar.setDisplayHomeAsUpEnabled(true);