action button" android:showAsAction" not work

If your app is using the Support Library for
compatibility on versions as low as Android 2.1,

the

showAsAction

attribute
is not available from the

android:

namespace.
Instead this attribute is provided by the Support Library and you must define your own XML namespace and use that namespace as the attribute prefix. (A custom XML namespace should be based on your app name, but it can be any name you want and is only accessible
within the scope of the file in which you declare it.)

For example:

<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:yourapp="http://schemas.android.com/apk/res-auto" >
<!-- Search, should appear as action button -->
<item android:id="@+id/action_search"
android:icon="@drawable/ic_action_search"
android:title="@string/action_search"
yourapp:showAsAction="ifRoom"  />
...
</menu>

好吧~~