Adding action bar action items

The fundamental purpose of an action bar, besides navigation, is to present the user with a set of actions that can be performed.

How to do it...

By simply using the action bar, all the action items are added to the overflow:

1. The XML for ActionBar items is exactly the same as the options menu:

   <menu ... >
     <item
       android:id="@+id/action_refresh"
       android:icon="@drawable/ic_action_refresh"
       android:title="@string/action_refresh"/>
   </menu>

However, we can customize what items are displayed, and how they are displayed:

1. To add action items with images to the actual ActionBar property, as well as more complex items, all that is needed is an attribute in the XML, showAsAction:

   <menu ... xmlns:app="http://schemas.android.com/apk/res-auto">
     <item ... app:showAsAction="ifRoom"/>
   </menu>

2. If we wish to add custom views, such as a search box, to the action bar, we make use of the actionViewClass attribute:

   <menu ... xmlns:app="http://schemas.android.com/apk/res-auto">
     <item ...
     app:actionViewClass="android.support.v7.widget.SearchView"/>
   </menu>

3. If the view is in a layout resource file, we use the actionLayout attribute:

   <menu ... xmlns:app="http://schemas.android.com/apk/res-auto">
     <item ... app:actionLayout="@layout/action_rating"/>
   </menu>

4. Sometimes, we may wish to only display the icon initially and then, when the user taps the icon, expand the item to display the action view:

   <menu ... xmlns:app="http://schemas.android.com/apk/res-auto">
     <item ... app:showAsAction="ifRoom|collapseActionView"/>
   </menu>

How it works...

Action item buttons are just traditional options menu items but are optionally always visible on the action bar.

The underlying logic to handle item selections is the same as that for the traditional options menu. No change is required to existing code inside the OnOptionsItemSelected() method.

The value of the showAsAction attribute can be ifRoom, never, or always. This value can optionally be combined, using a pipe, with withText and/or collapseActionView.