Menus are an important part of an application that provide a familiar interface for the user to access application functions and settings. Android offers an easy programming interface for you to provide application menus in your application.
Android provides three types of application menus:
Instead of instantiating Menu objects in your application code, you should
define a menu and all its items in an XML menu resource, then inflate the menu
resource (load it as a programmable object) in your application code. Defining your menus in XML is
a good practice because it separates your interface design from your application code (the same as
when you define your Activity
layout).
To define a menu, create an XML file inside your project's res/menu/
directory and build the menu with the following elements:
<menu>Menu, which is a container for menu items. It must be
the root node and holds one or more of the following elements. You can also nest this element
in an <item> to create a submenu.<item>MenuItem, which represents a single item in a menu.<group><item> elements. It allows you to
categorize menu items so they share properties such as active state and visibility. See Menu groups.For example, here is a file in res/menu/ named game_menu.xml:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/new_game"
android:icon="@drawable/ic_new_game"
android:title="@string/new_game" />
<item android:id="@+id/quit"
android:icon="@drawable/ic_quit"
android:title="@string/quit" />
</menu>
This example defines a menu with two menu items. Each item includes the attributes:
android:idandroid:iconandroid:titleFor more about the XML syntax and attributes for a menu resource, see the Menu Resource reference.
You can inflate your menu resource (convert the XML resource into a programmable object) using
MenuInflater.inflate(). For
example, the following code inflates the game_menu.xml file defined above during the
onCreateOptionsMenu() callback method, to be
used for the Options Menu:
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.game_menu, menu);
return true;
}
The getMenuInflater() method returns a MenuInflater for the Activity. With this object, you can call inflate(), which inflates a menu resource into a
Menu object. In this example, the menu resource defined by
game_menu.xml
is inflated into the Menu that was passed into onCreateOptionsMenu(). (This callback method for
creating an option menu is discussed more in the next section.)
Figure 1. Screenshot of an Options Menu.
The Options Menu is where you should include basic application functions and necessary navigation items (for example, a button to open application settings). The user can open the Options Menu with the device MENU key. Figure 1 shows a screenshot of an Options Menu.
When opened, the first visible portion of the Options Menu is called the Icon Menu. It holds the first six menu items. If you add more than six items to the Options Menu, Android places the sixth item and those after it into the Expanded Menu, which the user can open with the "More" menu item.
When the user opens the Options Menu for the first time, Android calls your Activity's
onCreateOptionsMenu() method. Override this method in your Activity
and populate the Menu that is passed into the method. Populate the
Menu by inflating a menu resource as described in Inflating a Menu Resource. (You can
also populate the menu in code, using add() to add menu items.)
When the user selects a menu item from the Options Menu, the system calls your Activity's
onOptionsItemSelected()
method. This method passes the
MenuItem that the user selected. You can identify the menu item by calling
getItemId(), which returns the unique ID for the menu
item (defined by the android:id attribute in the menu resource or with an integer passed
to the add() method). You can match this ID
against known menu items and perform the appropriate action.
For example:
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle item selection
switch (item.getItemId()) {
case R.id.new_game:
newGame();
return true;
case R.id.quit:
quit();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
In this example, getItemId() queries the ID for the selected menu
item and the switch statement compares the ID against the resource IDs that were assigned to menu
items in the XML resource. When a switch case successfully handles the item, it
returns "true" to indicate that the item selection was handled. Otherwise, the default statement
passes the menu item to the super class in
case it can handle the item selected. (If you've directly extended the Activity
class, then the super class returns "false", but it's a good practice to
pass unhandled menu items to the super class instead of directly returning "false".)
Tip: If your application contains multiple activities and
some of them provide the same Options Menu, consider creating
an Activity that implements nothing except the onCreateOptionsMenu() and onOptionsItemSelected() methods. Then extend this class for each Activity that should share the
same Options Menu. This way, you have to manage only one set of code for handling menu
actions and each decendent class inherits the menu behaviors.
If you want to add menu items to one of your decendent activities,
override onCreateOptionsMenu() in that Activity. Call super.onCreateOptionsMenu(menu) so the
original menu items are created, then add new menu items with menu.add(). You can also override the super class's
behavior for individual menu items.
The onCreateOptionsMenu() method is
called only the first time the Options Menu is opened. The system keeps and re-uses the Menu you define in this method until your Activity is destroyed. If you want to change
the Options Menu each time it opens, you must override the
onPrepareOptionsMenu() method. This passes
you the Menu object as it currently exists. This is useful if you'd like to
remove, add, disable, or enable menu items depending on the current state of your application.
Note:
You should never change items in the Options Menu based on the View currently
in focus. When in touch mode (when the user is not using a trackball or d-pad), Views
cannot take focus, so you should never use focus as the basis for modifying
items in the Options Menu. If you want to provide menu items that are context-sensitive to a View, use a Context Menu.
A context menu is conceptually similar to the menu displayed when the user performs a "right-click" on a PC. You should use a context menu to provide the user access to actions that pertain to a specific item in the user interface. On Android, a context menu is displayed when the user performs a "long press" (press and hold) on an item.
You can create a context menu for any View, though context menus are most often used for items in
a ListView. When the user performs a long-press on an item in a ListView and
the list is registered to provide a context menu, the list item signals to the user that a context
menu is available by animating its background color—it transitions from
orange to white before opening the context menu. (The Contacts application demonstrates this
feature.)
If your Activity uses a ListView and
you want all list items to provide a context menu, register all items for a context
menu by passing the ListView to registerForContextMenu(). For
example, if you're using a ListActivity, register all list items like this:
registerForContextMenu(getListView());
In order for a View to provide a context menu, you must "register" the view for a context
menu. Call registerForContextMenu() and
pass it the View you want to give a context menu. When this View then
receives a long-press, it displays a context menu.
To define the context menu's appearance and behavior, override your Activity's context menu
callback methods, onCreateContextMenu() and
onContextItemSelected().
For example, here's an onCreateContextMenu() that uses the context_menu.xml menu resource:
@Override
public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenuInfo menuInfo) {
super.onCreateContextMenu(menu, v, menuInfo);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.context_menu, menu);
}
MenuInflater is used to inflate the context menu from a menu resource. (You can also use
add() to add menu items.) The callback method
parameters include the View
that the user selected and a ContextMenu.ContextMenuInfo object that provides
additional information about the item selected. You might use these parameters to determine
which context menu should be created, but in this example, all context menus for the Activity are
the same.
Then when the user selects an item from the context menu, the system calls onContextItemSelected(). Here is an example
of how you can handle selected items:
@Override
public boolean onContextItemSelected(MenuItem item) {
AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
switch (item.getItemId()) {
case R.id.edit:
editNote(info.id);
return true;
case R.id.delete:
deleteNote(info.id);
return true;
default:
return super.onContextItemSelected(item);
}
}
The structure of this code is similar to the example for Creating an
Options Menu, in which getItemId() queries the ID for the selected
menu item and a switch statement matches the item to the IDs that are defined in the menu resource.
And like the options menu example, the default statement calls the super class in case it
can handle menu items not handled here, if necessary.
In this example, the selected item is an item from a ListView. To
perform an action on the selected item, the application needs to know the list
ID for the selected item (it's position in the ListView). To get the ID, the application calls
getMenuInfo(), which returns a AdapterView.AdapterContextMenuInfo object that includes the list ID for the
selected item in the id field. The
local methods editNote() and deleteNote() methods accept this list ID to
perform an action on the data specified by the list ID.
Note: Items in a context menu do not support icons or shortcut keys.
A submenu is a menu that the user can open by selecting an item in another menu. You can add a submenu to any menu (except a submenu). Submenus are useful when your application has a lot of functions that can be organized into topics, like items in a PC application's menu bar (File, Edit, View, etc.).
When creating your menu
resource, you can create a submenu by adding a <menu> element as the child of an
<item>. For example:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/file"
android:icon="@drawable/file"
android:title="@string/file" >
<!-- "file" submenu -->
<menu">
<item android:id="@+id/new"
android:title="@string/new" />
<item android:id="@+id/open"
android:title="@string/open" />
</menu>
</item>
</menu>
When the user selects an item from a submenu, the parent menu's respective on-item-selected
callback method receives the event. For instance, if the above menu is applied as an Options Menu,
then the onOptionsItemSelected() method
is called when a submenu item is selected.
You can also use addSubMenu() to
dynamically add a SubMenu to an existing Menu. This
returns the new SubMenu object, to which you can add
submenu items, using add()
Here are some other features that you can apply to most menu items.
A menu group is a collection of menu items that share certain traits. With a group, you can:
setGroupVisible()setGroupEnabled()setGroupCheckable()You can create a group by nesting <item> elements inside a <group>
element in your menu resource or by specifying a group ID with the the add() method.
Here's an example menu resource that includes a group:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/item1"
android:icon="@drawable/item1"
android:title="@string/item1" />
<!-- menu group -->
<group android:id="@+id/group1">
<item android:id="@+id/groupItem1"
android:title="@string/groupItem1" />
<item android:id="@+id/groupItem2"
android:title="@string/groupItem2" />
</group>
</menu>
The items that are in the group appear the same as the first item that is not in a group—all three items in the menu are siblings. However, you can modify the traits of the two items in the group by referencing the group ID and using the methods listed above.
Figure 2. Screenshot of checkable menu items
A menu can be useful as an interface for turning options on and off, using a checkbox for stand-alone options, or radio buttons for groups of mutually exclusive options. Figure 2 shows a submenu with items that are checkable with radio buttons.
Note: Menu items in the Icon Menu (from the Options Menu) cannot display a checkbox or radio button. If you choose to make items in the Icon Menu checkable, you must manually indicate the checked state by swapping the icon and/or text each time the state changes.
You can define the checkable behavior for individual menu items using the android:checkable attribute in the <item> element, or for an entire group with
the android:checkableBehavior attribute in the <group> element. For
example, all items in this menu group are checkable with a radio button:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<group android:checkableBehavior="single">
<item android:id="@+id/red"
android:title="@string/red" />
<item android:id="@+id/blue"
android:title="@string/blue" />
</group>
</menu>
The android:checkableBehavior attribute accepts either:
singleallnoneYou can apply a default checked state to an item using the android:checked attribute in
the <item> element and change it in code with the setChecked() method.
When a checkable item is selected, the system calls your respective item-selected callback method
(such as onOptionsItemSelected()). It
is here that you must set the state of the checkbox, because a checkbox or radio button does not
change its state automatically. You can query the current state of the item (as it was before the
user selected it) with isChecked() and then set the checked state with
setChecked(). For example:
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.vibrate:
case R.id.dont_vibrate:
if (item.isChecked()) item.setChecked(false);
else item.setChecked(true);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
If you don't set the checked state this way, then the visible state of the item (the checkbox or radio button) will not change when the user selects it. When you do set the state, the Activity preserves the checked state of the item so that when the user opens the menu later, the checked state that you set is visible.
Note: Checkable menu items are intended to be used only on a per-session basis and not saved after the application is destroyed. If you have application settings that you would like to save for the user, you should store the data using Shared Preferences.
You can add quick-access shortcut keys using letters and/or numbers to menu items with the
android:alphabeticShortcut and android:numericShortcut attributes in the <item> element. You can also use the methods setAlphabeticShortcut(char) and setNumericShortcut(char). Shortcut keys are not
case sensitive.
For example, if you apply the "s" character as an alphabetic shortcut to a "save" menu item, then when the menu is open (or while the user holds the MENU key) and the user presses the "s" key, the "save" menu item is selected.
This shortcut key is displayed as a tip in the menu item, below the menu item name (except for items in the Icon Menu, which are displayed only if the user holds the MENU key).
Note: Shortcut keys for menu items only work on devices with a hardware keyboard. Shortcuts cannot be added to items in a Context Menu.
Sometimes you'll want a menu item to launch an Activity using an Intent (whether it's an
Actvitity in your application or another application). When you know the Intent you want to use and
have a specific menu item that should initiate the Intent, you can execute the Intent with startActivity() during the appropriate on-item-selected
callback method (such as the onOptionsItemSelected() callback).
However, if you are not certain that the user's device contains an application that handles the Intent, then adding a menu item that executes the Intent can result in a non-functioning menu item, because the Intent might not resolve to an Activity that accepts it. To solve this, Android lets you dynamically add menu items to your menu when Android finds activities on the device that handle your Intent.
If you're not familiar with creating Intents, read the Intents and Intent Filters.
When you don't know if the user's device has an application that handles a specific Intent, you can define the Intent and let Android search the device for activities that accept the Intent. When it finds activies that handle the Intent, it adds a menu item for each one to your menu and attaches the appropriate Intent to open the Activity when the user selects it.
To add menu items based on available activities that accept an Intent:
CATEGORY_ALTERNATIVE and/or
CATEGORY_SELECTED_ALTERNATIVE, plus any other requirements.Menu.addIntentOptions(). Android then searches for any applications that can perform the Intent
and adds them to your menu.If there are no applications installed that satisfy the Intent, then no menu items are added.
Note:
CATEGORY_SELECTED_ALTERNATIVE is used to handle the currently
selected element on the screen. So, it should only be used when creating a Menu in onCreateContextMenu().
For example:
@Override
public boolean onCreateOptionsMenu(Menu menu){
super.onCreateOptionsMenu(menu);
// Create an Intent that describes the requirements to fulfill, to be included
// in our menu. The offering app must include a category value of Intent.CATEGORY_ALTERNATIVE.
Intent intent = new Intent(null, dataUri);
intent.addCategory(Intent.CATEGORY_ALTERNATIVE);
// Search and populate the menu with acceptable offering applications.
menu.addIntentOptions(
R.id.intent_group, // Menu group to which new items will be added
0, // Unique item ID (none)
0, // Order for the items (none)
this.getComponentName(), // The current Activity name
null, // Specific items to place first (none)
intent, // Intent created above that describes our requirements
0, // Additional flags to control items (none)
null); // Array of MenuItems that correlate to specific items (none)
return true;
}
For each Activity found that provides an Intent filter matching the Intent defined, a menu
item is added, using the value in the Intent filter's android:label as the
menu item title and the application icon as the menu item icon. The
addIntentOptions() method returns the number of menu items added.
Note: When you call addIntentOptions(), it overrides any and all menu items by the menu group specified in the first
argument.
You can also offer the services of your Activity to other applications, so your application can be included in the menu of others (reverse the roles described above).
To be included in other application menus, you need to define an Intent
filter as usual, but be sure to include the CATEGORY_ALTERNATIVE
and/or CATEGORY_SELECTED_ALTERNATIVE values for the Intent filter
category. For example:
<intent-filter label="Resize Image">
...
<category android:name="android.intent.category.ALTERNATIVE" />
<category android:name="android.intent.category.SELECTED_ALTERNATIVE" />
...
</intent-filter>
Read more about writing Intent filters in the Intents and Intent Filters document.
For a sample application using this technique, see the Note Pad sample code.