android 为activity添加optionMenu选项菜单

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

     <group android:checkableBehavior="single">
         <item
                 android:id="@+id/contact_us"
                 android:orderInCategory="1"
                 android:showAsAction=""
                 android:title="联系我们"/>
         <item android:title="关于我们"/>
     </group>

    <group>
        <item android:title="系统设置"

              android:orderInCategory="2"
              android:icon="@drawable/ic_launcher"
              android:id="@+id/system_setting"
                >
            <menu>
                <item android:title="亮度设置" android:id="@+id/liangdu"/>
                <item android:enabled="false" android:title="主题设置" android:id="@+id/theme"/>
            </menu>
        </item>
    </group>


</menu>

 @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        new MenuInflater(this).inflate(R.menu.option_menu_main, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.liangdu:
                Toast.makeText(this, "点击了亮度", 1).show();
                startActivity(new Intent(this, LiangduActivity.class));
                break;
            case R.id.contact_us:
                Toast.makeText(this, "点击了关于我们", 1).show();
                break;
        }
        return true;
    }