Java _Android Simple Code: Chapter 12 :Menus and Action Bar

Menus and Action Bar

Definition of menu entries

Android provides two possible ways to display global actions which the user can select. The first one is the usage of the Action Bar in the application. The Action Bar is a window feature at the top of the activity that may display the activity title, navigation modes, and other interactive items.
The second option is that the app can open a menu which shows additional actions via a popup menu. Typically you define your menu entries in a way that they are added to the action bar if sufficient space is available in the action bar and if not, remaining menu items are displayed in the popup menu.
The option menu and the action bar of your activity is filled by the method onCreateOptionsMenu() of your activity.
The ActionBar also shows an icon of your application. You can also add an action to this icon. If you select this icon the onOptionsItemSelected() method will be called with the value android.R.id.home. The recommendation is to return to the main Activity in your program.

                                
// If home icon is clicked return to main Activity
case android.R.id.home:
        Intent intent = new Intent(this, OverviewActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(intent);
        break;

In this method you can create the menu programmatically or you can use a pre-defined XML resources which you inflate via the MenuInflator class. Each Activity has already an instance of the class available and this instance can get accessed via the getMenuInflator() method.
The onCreateOptionsMenu() method is only called once. If you want to influence the menu later you have to use the onPrepareOptionsMenu() method.

Action bar tabs

It is also possible to add tabs to an action bar.

Context menus

You can also assign a context menu to an UI widget (view). A context menu is activated if the user "long presses" the view.
A context menu for a view is registered via the registerForContextMenu(view) method. The onCreateContextMenu() method is called every time a context menu is activated as the context menu is discarded after its usage. The Android platform may also add options to your View, e.g. EditText provides context options to select text, etc.

Menus and Action Bar

Project

This chapter will demonstrate how to create and evaluate a option menu which is displayed in the action bar if sufficient space is available. This example will be extended in the chapter about preferences.
Create a project called "de.vogella.android.socialapp" with the Activity called "OverviewActivity". Change the "main.xml" layout file in the diretory "/res/layout/" to the following:

                                
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/Button01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Show Preferences" >
    </Button>

    <Button
        android:id="@+id/Button02"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Change Preferences" >
    </Button>

</LinearLayout>

13.2. Add a menu XML resource

Select your project, right click on it and select New → Other → Android → Android XML File to create a new XML resource.
Select the option "Menu", enter as File "mainmenu.xml" and press the button "Finish".

This will create a new file "mainmenu.xml" in the folder "res/menu" of your project. Android provides a nice editor to edit this file, unfortunately this editor is not always automatically used due to bugs in the ADT. If that happens, you can open this editor manually. Right-click on your menu file and select Open with → Android Menu Editor.
Switch if necessary to the "Layout" tab of the editor. Press Add and select "Item". Maintain the following value. This defines the entries in your menu. We will also define that the menu entry is displayed in the action bar if there is sufficient space available.

Change your Activity class "OverviewActivity" to the following. The OnCreateOptionsMenu method is used to create the menu. The behavior in "onOptionsItemSelected" is currently hard-coded to show a Toast and will soon call the preference settings. In case you want to disable or hide menu items you can use the method "onPrepareOptionsMenu" which is called every time the menu is called.

                                
package de.vogella.android.socialapp;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;

public class OverviewActivity extends Activity {
        @Override
        public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
                MenuInflater inflater = getMenuInflater();
                inflater.inflate(R.menu.mainmenu, menu);
                return true;
        }

        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
                Toast.makeText(this, "Just a test", Toast.LENGTH_SHORT).show();
                return true;
        }
}

Run your application. As there is enough space in the action bar your item will be displayed there. If there would be more items you could press "Menu" on the emulator to see them. If you select the menu item you should see a small info message.

Menu
Menus are a common user interface component in many types of applications. To provide a familiar and consistent user experience, you should use the Menu APIs to present user actions and other options in your activities.
Beginning with Android 3.0 (API level 11), Android-powered devices are no longer required to provide a dedicated Menu button. With this change, Android apps should migrate away from a dependence on the traditional 6-item menu panel and instead provide an action bar to present common user actions.
Although the design and user experience for some menu items have changed, the semantics to define a set of actions and options is still based on the Menu APIs. This guide shows how to create the three fundamental types of menus or action presentations on all versions of Android:

Options menu and action bar: The options menu is the primary collection of menu items for an activity. It's where you should place actions that have a global impact on the app, such as "Search," "Compose email," and "Settings."; If you're developing for Android 2.3 or lower, users can reveal the options menu panel by pressing the Menu button.; On Android 3.0 and higher, items from the options menu are presented by the action bar as a combination of on-screen action items and overflow options. Beginning with Android 3.0, the Menu button is deprecated (some devices don't have one), so you should migrate toward using the action bar to provide access to actions and other options.; See the section about Creating an Options Menu.
Context menu and contextual action mode: A context menu is a floating menu that appears when the user performs a long-click on an element. It provides actions that affect the selected content or context frame.; When developing for Android 3.0 and higher, you should instead use the contextual action mode to enable actions on selected content. This mode displays action items that affect the selected content in a bar at the top of the screen and allows the user to select multiple items.; See the section about Creating Contextual Menus.
Popup menu: A popup menu displays a list of items in a vertical list that's anchored to the view that invoked the menu. It's good for providing an overflow of actions that relate to specific content or to provide options for a second part of a command. Actions in a popup menu should not directly affect the corresponding content—that's what contextual actions are for. Rather, the popup menu is for extended actions that relate to regions of content in your activity.; See the section about Creating a Popup Menu.

Defining a Menu in XML

For all menu types, Android provides a standard XML format to define menu items. Instead of building a menu in your activity's code, you should define a menu and all its items in an XML menu resource. You can then inflate the menu resource (load it as a Menu object) in your activity or fragment.
Using a menu resource is a good practice for a few reasons:

It's easier to visualize the menu structure in XML.
It separates the content for the menu from your application's behavioral code.
It allows you to create alternative menu configurations for different platform versions, screen sizes, and other configurations by leveraging the app resources framework.

To define the menu, create an XML file inside your project's res/menu/ directory and build the menu with the following elements:

<menu>: Defines a Menu, which is a container for menu items. A <menu> element must be the root node for the file and can hold one or more <item> and <group> elements.
<item>: Creates a MenuItem, which represents a single item in a menu. This element may contain a nested <menu> element in order to create a submenu.
<group>: An optional, invisible container for <item> elements. It allows you to categorize menu items so they share properties such as active state and visibility. For more information, see the section about Creating Menu Groups.

Here's an example 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"
          android:showAsAction="ifRoom"/>
    <item android:id="@+id/help"
          android:icon="@drawable/ic_help"
          android:title="@string/help" />
</menu>

The <item> element supports several attributes you can use to define an item's appearance and behavior. The items in the above menu include the following attributes:

android:id: A resource ID that's unique to the item, which allows the application can recognize the item when the user selects it.
android:icon: A reference to a drawable to use as the item's icon.
android:title: A reference to a string to use as the item's title.
android:showAsAction: Specifies when and how this item should appear as an action item in the action bar.

These are the most important attributes you should use, but there are many more available. For information about all the supported attributes, see the Menu Resource document.
You can add a submenu to an item in any menu (except a submenu) by adding a <menu> element as the child of an <item>. 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.). 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:title="@string/file" >
        <!-- "file" submenu -->
        <menu>
            <item android:id="@+id/create_new"
                  android:title="@string/create_new" />
            <item android:id="@+id/open"
                  android:title="@string/open" />
        </menu>
    </item>
</menu>

To use the menu in your activity, you need to inflate the menu resource (convert the XML resource into a programmable object) using MenuInflater.inflate(). In the following sections, you'll see how to inflate a menu for each menu type.

Creating an Options Menu

Figure 1. Options menu in the Browser, on Android 2.3.
The options menu is where you should include actions and other options that are relevant to the current activity context, such as "Search," "Compose email," and "Settings."
Where the items in your options menu appear on the screen depends on the version for which you've developed your application:

If you've developed your application for Android 2.3.x (API level 10) or lower, the contents of your options menu appear at the bottom of the screen when the user presses the Menu button, as shown in figure 1. When opened, the first visible portion is the icon menu, which holds up to six menu items. If your menu includes more than six items, Android places the sixth item and the rest into the overflow menu, which the user can open by selecting More.
If you've developed your application for Android 3.0 (API level 11) and higher, items from the options menu are available in the action bar. By default, the system places all items in the action overflow, which the user can reveal with the action overflow icon on the right side of the action bar (or by pressing the device Menu button, if available). To enable quick access to important actions, you can promote a few items to appear in the action bar by adding android:showAsAction="ifRoom" to the corresponding <item> elements (see figure 2).
For more information about action items and other action bar behaviors, see the Action Bar guide.
Note: Even if you're not developing for Android 3.0 or higher, you can build your own action bar layout for a similar effect. For an example of how you can support older versions of Android with an action bar, see the Action Bar Compatibility sample.

Figure 2. Action bar from the Honeycomb Gallery app, showing navigation tabs and a camera action item (plus the action overflow button).
You can declare items for the options menu from either your Activity subclass or a Fragment subclass. If both your activity and fragment(s) declare items for the options menu, they are combined in the UI. The activity's items appear first, followed by those of each fragment in the order in which each fragment is added to the activity. If necessary, you can re-order the menu items with the android:orderInCategory attribute in each <item> you need to move.
To specify the options menu for an activity, override onCreateOptionsMenu() (fragments provide their own onCreateOptionsMenu() callback). In this method, you can inflate your menu resource (defined in XML) into the Menu provided in the callback. For example:

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.game_menu, menu);
    return true;
}

You can also add menu items using add() and retrieve items with findItem() to revise their properties with MenuItem APIs.
If you've developed your application for Android 2.3.x and lower, the system calls onCreateOptionsMenu() to create the options menu when the user opens the menu for the first time. If you've developed for Android 3.0 and higher, the system calls onCreateOptionsMenu() when starting the activity, in order to show items to the action bar.

Handling click events

When the user selects an item from the options menu (including action items in the action bar), the system calls your activity's onOptionsItemSelected() method. This method passes the MenuItem selected. You can identify the 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 given to the add() method). You can match this ID against known menu items to 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.help:
            showHelp();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

When you successfully handle a menu item, return true. If you don't handle the menu item, you should call the superclass implementation of onOptionsItemSelected() (the default implementation returns false).
If your activity includes fragments, the system first calls onOptionsItemSelected() for the activity then for each fragment (in the order each fragment was added) until one returns true or all fragments have been called.
Tip: Android 3.0 adds the ability for you to define the on-click behavior for a menu item in XML, using the android:onClick attribute. The value for the attribute must be the name of a method defined by the activity using the menu. The method must be public and accept a single MenuItem parameter—when the system calls this method, it passes the menu item selected. For more information and an example, see the Menu Resource document.
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 can manage one set of code for handling menu actions and each descendant class inherits the menu behaviors. If you want to add menu items to one of the descendant 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.

Changing menu items at runtime

After the system calls onCreateOptionsMenu(), it retains an instance of the Menu you populate and will not call onCreateOptionsMenu() again unless the menu is invalidated for some reason. However, you should use onCreateOptionsMenu() only to create the initial menu state and not to make changes during the activity lifecycle.
If you want to modify the options menu based on events that occur during the activity lifecycle, you can do so in the onPrepareOptionsMenu() method. This method passes you the Menu object as it currently exists so you can modify it, such as add, remove, or disable items. (Fragments also provide an onPrepareOptionsMenu() callback.)
On Android 2.3.x and lower, the system calls onPrepareOptionsMenu() each time the user opens the options menu (presses the Menu button).
On Android 3.0 and higher, the options menu is considered to always be open when menu items are presented in the action bar. When an event occurs and you want to perform a menu update, you must call invalidateOptionsMenu() to request that the system call onPrepareOptionsMenu().
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.

Creating Contextual Menus

Figure 3. Screenshots of a floating context menu (left) and the contextual action bar (right).
A contextual menu offers actions that affect a specific item or context frame in the UI. You can provide a context menu for any view, but they are most often used for items in a ListView, GridView, or other view collections in which the user can perform direct actions on each item.
There are two ways to provide contextual actions:

In a floating context menu. A menu appears as a floating list of menu items (similar to a dialog) when the user performs a long-click (press and hold) on a view that declares support for a context menu. Users can perform a contextual action on one item at a time.
In the contextual action mode. This mode is a system implementation of ActionMode that displays a contextual action bar at the top of the screen with action items that affect the selected item(s). When this mode is active, users can perform an action on multiple items at once (if your app allows it).

Note: The contextual action mode is available on Android 3.0 (API level 11) and higher and is the preferred technique for displaying contextual actions when available. If your app supports versions lower than 3.0 then you should fall back to a floating context menu on those devices.

Creating a floating context menu

To provide a floating context menu:

Register the View to which the context menu should be associated by calling registerForContextMenu() and pass it the View.
If your activity uses a ListView or GridView and you want each item to provide the same context menu, register all items for a context menu by passing the ListView or GridView to registerForContextMenu().
Implement the onCreateContextMenu() method in your Activity or Fragment.
When the registered view receives a long-click event, the system calls your onCreateContextMenu() method. This is where you define the menu items, usually by inflating a menu resource. For example:
```
@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 allows you to inflate the context menu from a menu resource. The callback method parameters include the View that the user selected and a ContextMenu.ContextMenuInfo object that provides additional information about the item selected. If your activity has several views that each provide a different context menu, you might use these parameters to determine which context menu to inflate.
Implement onContextItemSelected().
When the user selects a menu item, the system calls this method so you can perform the appropriate action. For example:
```
@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 getItemId() method queries the ID for the selected menu item, which you should assign to each menu item in XML using the android:id attribute, as shown in the section about Defining a Menu in XML.
When you successfully handle a menu item, return true. If you don't handle the menu item, you should pass the menu item to the superclass implementation. If your activity includes fragments, the activity receives this callback first. By calling the superclass when unhandled, the system passes the event to the respective callback method in each fragment, one at a time (in the order each fragment was added) until true or false is returned. (The default implementation for Activity and android.app.Fragment return false, so you should always call the superclass when unhandled.)

Using the contextual action mode

The contextual action mode is a system implementation of ActionMode that focuses user interaction toward performing contextual actions. When a user enables this mode by selecting an item, a contextual action bar appears at the top of the screen to present actions the user can perform on the currently selected item(s). While this mode is enabled, the user can select multiple items (if you allow it), deselect items, and continue to navigate within the activity (as much as you're willing to allow). The action mode is disabled and the contextual action bar disappears when the user deselects all items, presses the BACK button, or selects the Done action on the left side of the bar.
Note: The contextual action bar is not necessarily associated with the action bar. They operate independently, even though the contextual action bar visually overtakes the action bar position.
If you're developing for Android 3.0 (API level 11) or higher, you should usually use the contextual action mode to present contextual actions, instead of the floating context menu.
For views that provide contextual actions, you should usually invoke the contextual action mode upon one of two events (or both):

The user performs a long-click on the view.
The user selects a checkbox or similar UI component within the view.

How your application invokes the contextual action mode and defines the behavior for each action depends on your design. There are basically two designs:

For contextual actions on individual, arbitrary views.
For batch contextual actions on groups of items in a ListView or GridView (allowing the user to select multiple items and perform an action on them all).

The following sections describe the setup required for each scenario.

Enabling the contextual action mode for individual views

If you want to invoke the contextual action mode only when the user selects specific views, you should:

Implement the ActionMode.Callback interface. In its callback methods, you can specify the actions for the contextual action bar, respond to click events on action items, and handle other lifecycle events for the action mode.
Call startActionMode() when you want to show the bar (such as when the user long-clicks the view).

For example:

Implement the ActionMode.Callback interface:

private ActionMode.Callback mActionModeCallback = new ActionMode.Callback() {
    // Called when the action mode is created; startActionMode() was called
    @Override
    public boolean onCreateActionMode(ActionMode mode, Menu menu) {
        // Inflate a menu resource providing context menu items
        MenuInflater inflater = mode.getMenuInflater();
        inflater.inflate(R.menu.context_menu, menu);
        return true;
    }
    // Called each time the action mode is shown. Always called after onCreateActionMode, but
    // may be called multiple times if the mode is invalidated.
    @Override
    public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
        return false; // Return false if nothing is done
    }
    // Called when the user selects a contextual menu item
    @Override
    public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
        switch (item.getItemId()) {
            case R.id.menu_share:
                shareCurrentItem();
                mode.finish(); // Action picked, so close the CAB
                return true;
            default:
                return false;
        }
    }
    // Called when the user exits the action mode
    @Override
    public void onDestroyActionMode(ActionMode mode) {
        mActionMode = null;
    }
};

Notice that these event callbacks are almost exactly the same as the callbacks for the options menu, except each of these also pass the ActionMode object associated with the event. You can use ActionMode APIs to make various changes to the CAB, such as revise the title and subtitle with setTitle() and setSubtitle() (useful to indicate how many items are selected).
Also notice that the above sample sets the mActionMode variable null when the action mode is destroyed. In the next step, you'll see how it's initialized and how saving the member variable in your activity or fragment can be useful.

Call startActionMode() to enable the contextual action mode when appropriate, such as in response to a long-click on a View:
```
someView.setOnLongClickListener(new View.OnLongClickListener() {
    // Called when the user long-clicks on someView
    public boolean onLongClick(View view) {
        if (mActionMode != null) {
            return false;
        }
        // Start the CAB using the ActionMode.Callback defined above
        mActionMode = getActivity().startActionMode(mActionModeCallback);
        view.setSelected(true);
        return true;
    }
});
```
When you call startActionMode(), the system returns the ActionMode created. By saving this in a member variable, you can make changes to the contextual action bar in response to other events. In the above sample, the ActionMode is used to ensure that the ActionMode instance is not recreated if it's already active, by checking whether the member is null before starting the action mode.

Enabling batch contextual actions in a ListView or GridView

If you have a collection of items in a ListView or GridView (or another extension of AbsListView) and want to allow users to perform batch actions, you should:

Implement the AbsListView.MultiChoiceModeListener interface and set it for the view group with setMultiChoiceModeListener(). In the listener's callback methods, you can specify the actions for the contextual action bar, respond to click events on action items, and handle other callbacks inherited from the ActionMode.Callback interface.
Call setChoiceMode() with the CHOICE_MODE_MULTIPLE_MODAL argument.

For example:

ListView listView = getListView();
listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE_MODAL);
listView.setMultiChoiceModeListener(new MultiChoiceModeListener() {
    @Override
    public void onItemCheckedStateChanged(ActionMode mode, int position,
                                          long id, boolean checked) {
        // Here you can do something when items are selected/de-selected,
        // such as update the title in the CAB
    }
    @Override
    public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
        // Respond to clicks on the actions in the CAB
        switch (item.getItemId()) {
            case R.id.menu_delete:
                deleteSelectedItems();
                mode.finish(); // Action picked, so close the CAB
                return true;
            default:
                return false;
        }
    }
    @Override
    public boolean onCreateActionMode(ActionMode mode, Menu menu) {
        // Inflate the menu for the CAB
        MenuInflater inflater = mode.getMenuInflater();
        inflater.inflate(R.menu.context, menu);
        return true;
    }
    @Override
    public void onDestroyActionMode(ActionMode mode) {
        // Here you can make any necessary updates to the activity when
        // the CAB is removed. By default, selected items are deselected/unchecked.
    }
    @Override
    public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
        // Here you can perform updates to the CAB due to
        // an invalidate() request
        return false;
    }
});

That's it. Now when the user selects an item with a long-click, the system calls the onCreateActionMode() method and displays the contextual action bar with the specified actions. While the contextual action bar is visible, users can select additional items.
In some cases in which the contextual actions provide common action items, you might want to add a checkbox or a similar UI element that allows users to select items, because they might not discover the long-click behavior. When a user selects the checkbox, you can invoke the contextual action mode by setting the respective list item to the checked state with setItemChecked().

Creating a Popup Menu

Figure 4. A popup menu in the Gmail app, anchored to the overflow button at the top-right.
A PopupMenu is a modal menu anchored to a View. It appears below the anchor view if there is room, or above the view otherwise. It's useful for:

Providing an overflow-style menu for actions that relate to specific content (such as Gmail's email headers, shown in figure 4).
Note: This is not the same as a context menu, which is generally for actions that affect selected content. For actions that affect selected content, use the contextual action mode or floating context menu.
Providing a second part of a command sentence (such as a button marked "Add" that produces a popup menu with different "Add" options).
Providing a drop-down similar to Spinner that does not retain a persistent selection.

Note: PopupMenu is available with API level 11 and higher.
If you define your menu in XML, here's how you can show the popup menu:

Instantate a PopupMenu with its constructor, which takes the current application Context and the View to which the menu should be anchored.
Use MenuInflater to inflate your menu resource into the Menu object returned by PopupMenu.getMenu(). On API level 14 and above, you can use PopupMenu.inflate() instead.
Call PopupMenu.show().

For example, here's a button with the android:onClick attribute that shows a popup menu:

<ImageButton
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:src="@drawable/ic_overflow_holo_dark"
    android:contentDescription="@string/descr_overflow_button"
    android:onClick="showPopup" />

The activity can then show the popup menu like this:

public void showPopup(View v) {
    PopupMenu popup = new PopupMenu(this, v);
    MenuInflater inflater = popup.getMenuInflater();
    inflater.inflate(R.menu.actions, popup.getMenu());
    popup.show();
}

In API level 14 and higher, you can combine the two lines that inflate the menu with PopupMenu.inflate().
The menu is dismissed when the user selects an item or touches outside the menu area. You can listen for the dismiss event using PopupMenu.OnDismissListener.

Handling click events

To perform an action when the user selects a menu item, you must implement the PopupMenu.OnMenuItemClickListener interface and register it with your PopupMenu by calling setOnMenuItemclickListener(). When the user selects an item, the system calls the onMenuItemClick() callback in your interface.
For example:

public void showMenu(View v) {
    PopupMenu popup = new PopupMenu(this, v);
    // This activity implements OnMenuItemClickListener
    popup.setOnMenuItemClickListener(this);
    popup.inflate(R.menu.actions);
    popup.show();
}
@Override
public boolean onMenuItemClick(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.archive:
            archive(item);
            return true;
        case R.id.delete:
            delete(item);
            return true;
        default:
            return false;
    }
}

Creating Menu Groups

A menu group is a collection of menu items that share certain traits. With a group, you can:

Show or hide all items with setGroupVisible()
Enable or disable all items with setGroupEnabled()
Specify whether all items are checkable with 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/menu_save"
          android:icon="@drawable/menu_save"
          android:title="@string/menu_save" />
    <!-- menu group -->
    <group android:id="@+id/group_delete">
        <item android:id="@+id/menu_archive"
              android:title="@string/menu_archive" />
        <item android:id="@+id/menu_delete"
              android:title="@string/menu_delete" />
    </group>
</menu>

The items that are in the group appear at the same level as the first item—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. The system will also never separate grouped items. For example, if you declare android:showAsAction="ifRoom" for each item, they will either both appear in the action bar or both appear in the action overflow.

Using checkable menu items

Figure 5. Screenshot of a submenu with checkable 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 5 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:

single: Only one item from the group can be checked (radio buttons)
all: All items can be checked (checkboxes)
none: No items are checkable

You 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.

Adding Menu Items Based on an Intent

Sometimes you'll want a menu item to launch an activity using an Intent (whether it's an activity 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 invokes it can result in a non-functioning menu item, because the intent might not resolve to an activity. To solve this, Android lets you dynamically add menu items to your menu when Android finds activities on the device that handle your intent.
To add menu items based on available activities that accept an intent:

Define an intent with the category CATEGORY_ALTERNATIVE and/or CATEGORY_SELECTED_ALTERNATIVE, plus any other requirements.
Call 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.

Allowing your activity to be added to other menus

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="@string/resize_image">
    ...
    <category android:name="android.intent.category.ALTERNATIVE" />
    <category android:name="android.intent.category.SELECTED_ALTERNATIVE" />
    ...
</intent-filter>

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Wednesday, 14 March 2012

Chapter 12 :Menus and Action Bar

Menus and Action Bar

Definition of menu entries

Action bar tabs

Context menus

Menus and Action Bar

Project

13.2. Add a menu XML resource

Defining a Menu in XML

Creating an Options Menu

Handling click events

Changing menu items at runtime

Creating Contextual Menus

Creating a floating context menu

Using the contextual action mode

Enabling the contextual action mode for individual views

Enabling batch contextual actions in a ListView or GridView

Creating a Popup Menu

Handling click events

Creating Menu Groups

Using checkable menu items

Adding Menu Items Based on an Intent

Allowing your activity to be added to other menus

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