[Android] Action Bar - (1)

[Android 3.0]

• A replacement for the traditional title bar at the top of the activity window. Includes:
• The application logo in the left corner.
• Provides a new interface for items in the Options Menu.
• Can provide:
• Action items
• Equal to option menu items.
• Using android:showAsAction menu item xml attribute with a value of "ifRoom"
• When there's enough room
• The menu item appears directly in the Action Bar.
• Otherwise
• The item is placed in the overflow menu, revealed by the menu icon on the right side of the Action Bar.
• By default all items from the Options Menu are placed in the overflow menu.
• The user can open by touching the menu icon on the right side of the Action Bar.
• However, you can place select menu items directly in the Action Bar as "action items," for instant access
• Action view
• Replace an action item with a widget, ex: search box.
• Using android:actionViewLayout(android:actionLayout?) attribute with a layout resource or the android:actionViewClass attribute with the class name of a widget.
• You must also declare the android:showAsAction attribute so that the item appears in the Action Bar.
• If there's not enough room in the Action Bar does not show the widget.
• Add an action to the application logo and replace it with a custom logo
• The application logo is automatically assigned the android.R.id.home ID, which the system delivers to your activity's onOptionsItemSelected() callback when touched.
• Simply respond to this ID in your callback method to perform an action such as go to your application's "home" activity.
• To replace the icon with a logo.
• Specify your application logo in the manifest file with the android:logo attribute, then call setDisplayUseLogoEnabled(true) in your activity.
• Add breadcrumbs to navigate backward through the back stack of fragments.
• Add tabs or a drop-down list to navigate through fragments.
• Customize the Action Bar with themes and backgrounds.

Summary

• action items = options menu = overflow action items (ifRoom)
• context menu: showing after long press
• Displayed when the user performs a "right-click" on a PC.
• 需覆寫 onCreateContextMenu() 及 onContextItemSelected()
• action view: widget(search box)

By the way

• Menu items could define in res/menu/filename.xml.
• Options menu
• Items are accessible in two distinct ways: 
• The MENU button. (at the bottom)
• In the Action Bar (on devices running Android 3.0 or higher). (at the top)
• The primary collection of menu items for an activity.
• Cannot display a checkbox or radio button.
• Related APIs
• onCreateOptionsMenu()
• Is called only once.
• Note: 
• On Android 2.3 and lower
• The system calls this to create the Options Menu when the user opens it for the first time.
• On Android 3.0 and greater
• The system creates it as soon as the activity is created, in order to populate the Action Bar.
• MenuInflater.inflate()
• onOptionsItemSelected()/android:onClick(API 11)
• onPrepareOptionsMenu() 
• If you want to provide menu items that are context-sensitive to a View, use a Context Menu.
• On Android 2.3 and lower
• The system calls this each time the user opens the Options Menu.
• On Android 3.0 and higher
• You must call invalidateOptionsMenu() when you want to update the menu, because the menu is always open.
• The system will then call onPrepareOptionsMenu() so you can update the menu items.
• Context menu
• Must "register" the view for a context menu. 
• Call registerForContextMenu() and pass it the View you want to give a context menu.
• Related APIs
• onCreateContextMenu()
• onContextItemSelected()
• onContextItemSelected()
• ContextMenu.ContextMenuInfo
• AdapterView.AdapterContextMenuInfo
• Includes the list ID for the selected item in the id field.
• SubMenu
• A menu that the user can open by selecting an item in another menu.

* Reference
- Android 3.0 Platform | Android Developers
- Menu Resource

- Android學習筆記 - 長按選單(ContextMenu)
- Menus | Android Developers