Adding an Action View

　　An action view is a widget that appears in the action bar as a substitute for an action button. An action view provides fast access to rich actions without changing activities or fragments, and without replacing the action bar. For example, if you have an action for Search, you can add an action view to embeds a SearchView widget in the action bar, as shown in figure 5.

Figure 5. An action bar with a collapsible SearchView.

　　To declare an action view, use either the actionLayout or actionViewClass attribute to specify either a layout resource or widget class to use, respectively. For example, here's how to add the SearchView widget:

 <?xml version="1.0" encoding="utf-8"?>
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:yourapp="http://schemas.android.com/apk/res-auto" >
     <item android:id="@+id/action_search"
           android:title="@string/action_search"
           android:icon="@drawable/ic_action_search"
           yourapp:showAsAction="ifRoom|collapseActionView"
           yourapp:actionViewClass="android.support.v7.widget.SearchView" />
 </menu>

　　Notice that the showAsAction attribute also includes the "collapseActionView" value. This is optional and declares that the action view should be collapsed into a button. (This behavior is explained further in the following section about Handling collapsible action views.)

　　android:showAsAction="collapseActionView" 是可折叠自定义的view

　　If you need to configure the action view (such as to add event listeners), you can do so during the onCreateOptionsMenu() callback. You can acquire the action view object by calling the static method MenuItemCompat.getActionView() and passing it the corresponding MenuItem. For example, the search widget from the above sample is acquired like this:

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
     getMenuInflater().inflate(R.menu.main_activity_actions, menu);
     MenuItem searchItem = menu.findItem(R.id.action_search);
     SearchView searchView = (SearchView) MenuItemCompat.getActionView(searchItem);
     // Configure the search info and add any event listeners
     ...
     return super.onCreateOptionsMenu(menu);
 }

　　在api 11 以前 可以在onCreateOptionsMenu()函数中,通过MenuItemCompat.getActionView(xxItem) 得到它自定义的view,然后给这个view注册事件函数等.

On API level 11 or higher

　　Get the action view by calling getActionView() on the corresponding MenuItem:

menu.findItem(R.id.action_search).getActionView();

　　在api 11 以后 可以在onCreateOptionsMenu()函数中,直接通过item.getActionView() 得到它自定义的view,然后给这个view注册事件函数等.

　　For more information about using the search widget, see Creating a Search Interface.

Handling collapsible action views

　　To preserve the action bar space, you can collapse your action view into an action button. When collapsed, the system might place the action into the action overflow, but the action view still appears in the action bar when the user selects it. You can make your action view collapsible by adding "collapseActionView" to the showAsAction attribute, as shown in the XML above.

　　Because the system expands the action view when the user selects the action, you do not need to respond to the item in the onOptionsItemSelected() callback. The system still calls onOptionsItemSelected(), but if you return true (indicating you've handled the event instead), then the action view will not expand.

　　The system also collapses your action view when the user presses the Up button or Back button.

　　If you need to update your activity based on the visibility of your action view, you can receive callbacks when the action is expanded and collapsed by defining an OnActionExpandListener and passing it to setOnActionExpandListener(). For example:

　　collapseActionView 属性值表示把自定义的action view折叠到溢出菜单中.每个操作项可以注册折叠事件接口 OnActionExpandListener 得到

　　展开事件回调: onMenuItemActionExpand

　　折叠事件回调: onMenuItemActionCollapse

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
     getMenuInflater().inflate(R.menu.options, menu);
     MenuItem menuItem = menu.findItem(R.id.actionItem);
     ...

     // When using the support library, the setOnActionExpandListener() method is
     // static and accepts the MenuItem object as an argument
     MenuItemCompat.setOnActionExpandListener(menuItem, new OnActionExpandListener() {
         @Override
         public boolean onMenuItemActionCollapse(MenuItem item) {
             // Do something when collapsed
             return true;  // Return true to collapse action view
         }

         @Override
         public boolean onMenuItemActionExpand(MenuItem item) {
             // Do something when expanded
             return true;  // Return true to expand action view
         }
     });
 }