Beginning Android

Menu XML Structure

Menu XML goes in res/menu/ in your project tree, alongside the other types of resources that your project might employ. As with layouts, you can have several menu XML files in your project, each with their own filename and the .xml extension.

For example, from the Menus/Inflation sample project at http://apress.com/, here is a menu called sample.xml:

<?xml version='1.0' encoding='utf-8'?>
<menu xmlns:android='http://schemas.android.com/apk/res/android'>
 <item android:id='@+id/close'
  android:title='Close'
  android:orderInCategory='3'
  android:icon='@drawable/eject' />
 <item android:id='@+id/no_icon'
  android:orderInCategory='2'
  android:title='Sans Icon' />
 <item android:id='@+id/disabled'
  android:orderInCategory='4'
  android:enabled='false'
  android:title='Disabled' />
 <group android:id='@+id/other_stuff'
  android:menuCategory='secondary'
  android:visible='false'>
  <item android:id='@+id/later'
   android:orderInCategory='0'
   android:title='2nd-To-Last' />
  <item android:id='@+id/last'
   android:orderInCategory='1'
   android:title='Last' />
 </group>
 <item android:id='@+id/submenu'
  android:orderInCategory='3'
  android:title='A Submenu'>
  <menu>
   <item android:id='@+id/non_ghost'
    android:title='Non-Ghost'
    android:visible='true'
    android:alphabeticShortcut='n' />
   <item android:id='@+id/ghost'
    android:title='A Ghost'
    android:visible='false'
    android:alphabeticShortcut='g' />
  </menu>
 </item>
</menu>

Note the following about menu XML definitions:

• You must start with a menu root element.

• Inside a menu are item elements and group elements, the latter representing a collection of menu items that can be operated upon as a group.

• Sub-menus are specified by adding a menu element as a child of an item element, using this new menu element to describe the contents of the sub- menu.

• If you want to detect when an item is chosen or to reference an item or group from your Java code, be sure to apply an android:id, just as you do with View layout XML.

Menu Options and XML

Inside the item and group elements you can specify various options, matching up with corresponding methods on Menu or MenuItem.

Title

The title of a menu item is provided via the android:title attribute on an item element. This can be either a literal string or a reference to a string resource (e.g., @string/foo).

Icon

Menu items can have icons. To provide an icon — in the form of a reference to a drawable resource (e.g., @drawable/eject), use the android:icon attribute on the item element.

Order

By default, the order of the items in the menu is determined by the order they appear in the menu XML. If you want, you can change that default by specifying the android:orderInCategory attribute on the item element. This is a 0-based index of the order for the items associated with the current category. There is an implicit default category; groups can provide an android:menuCategory attribute to specify a different category to use for items in that group.

Generally, though, it is simplest just to put the items in the XML in the order you want them to appear.

Enabled

Items and groups can be enabled or disabled, controlled in the XML via the android:enabled attribute on the item or group element. By default, items and groups are enabled. Disabled items and groups appear in the menu but cannot be selected. You can change an item’s status at runtime via the setEnabled() method on MenuItem, or change a group’s status via setGroupEnabled() on Menu.

Visible

Similarly, items and groups can be visible or invisible, controlled in the XML via the android:visible attribute on the item or group element. By default, items and groups are visible. Invisible items and groups do not appear in the menu at all. You can change an item’s status at runtime via the setVisible() method on MenuItem, or change a group’s status via setGroupVisible() on Menu.

In the layout XML shown earlier, the other_stuff group is initially invisible. If we make it visible in our Java code, the two menu items in the group will “magically” appear.

Shortcut

Items can have shortcuts — single letters (android:alphabeticShortcut) or numbers (android:numericShortcut) that can be pressed to choose the item without having to use the touch screen, D-pad, or trackball to navigate the full menu.

Inflating a Menu

Actually using a menu, once it’s defined in XML, is easy. Just create a MenuInflater and tell