Android程序实现动态OptionsMenu 默认使用的菜单例子都是创建的静态菜单，在某些时候会不方便，比如： 一篇文章的显示，按menu有加入收藏的功能，那实现的是如果未加入收藏，则是加入收藏的操作，否则是取消收藏的操作。 但onCreateOptionsMenu是实现不了这个功能的，它只会运行一次，如果再次按下menu，则不会变化。
我们看看程序说明：
public boolean onCreateOptionsMenu (Menu menu)
Initialize the contents of the Activity's standard options menu. You should place your menu items in to menu.
This is only called once, the first time the options menu is displayed. To update the menu every time it is displayed, see onPrepareOptionsMenu(Menu).
The default implementation populates the menu with standard system menu items. These are placed in the CATEGORY_SYSTEM group so that they will be correctly ordered with application-defined menu items. Deriving classes should always call through to the base implementation.
You can safely hold on to menu (and any items created from it), making modifications to it as desired, until the next time onCreateOptionsMenu() is called.
When you add items to the menu, you can implement the Activity's onOptionsItemSelected(MenuItem) method to handle them there.
Parameters
menu The options menu in which you place your items.
Returns
You must return true for the menu to be displayed; if you return false it will not be shown.
See Also
onPrepareOptionsMenu(Menu)
onOptionsItemSelected(MenuItem)
也就是说明了它是第一次显示菜单时调用的，每次更新，需要定义onPrepareOptionsMenu:
public boolean onPrepareOptionsMenu (Menu menu)
Prepare the Screen's standard options menu to be displayed. This is called right before the menu is shown, every time it is shown. You can use this method to efficiently enable/disable items or otherwise dynamically modify the contents.
The default implementation updates the system menu items based on the activity's state. Deriving classes should always call through to the base class implementation. 代码例子： 01.
02.public boolean onPrepareOptionsMenu(Menu menu) {
03.menu.clear();
04.if(isFavoutite){
05.menu.add(0, NFav_ID, 0, R.string.menu_not_favourite).setIcon(R.drawable.ic_tab_selected_contacts);
06.}else{
07.menu.add(0, Fav_ID, 0, R.string.menu_favourite).setIcon(R.drawable.ic_tab_selected_contacts);
08.}
09.menu.add(0, Del_ID, 0, R.string.menu_delete).setIcon(R.drawable.ic_tab_selected_contacts);
10.return super.onPrepareOptionsMenu(menu);
11.}
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