올해는 머신러닝이다.

The action bar (ActionBar) is located at the top of the activity. It can display the activity title, icon, actions which can be triggered, additional views and other interactive items. It can also be used for navigation in your application.

The action bar is enabled for devices which specify a target SDK of API version 11 or higher. It is possible to disable the action bar via the used theme, but the default Android themes have it enabled.

Applications with a target SDK version less than API 11 use the options menu if such a button is present on the device. The option menu is displayed if the user presses the Option button. The action bar is superior to the options menu, as the action bar is clearly visible, while the options menu is only shown on request. In case of the options menu, the user may not recognize that options are available in the application.

The following screenshot shows the action bar of the Google+ Android application with interactive items and a navigation bar. On top it also indicates that the user can open a navigation bar on the side of the application.

The action bar has been introduced in Android 3.0. If you want to use the action bar on devices with an earlier Android release, you have two popular options.

First, you can use the Open Source project called ActionBar Sherlock which allows you to use the action bar on Android devices as of Android 1.6. You find this library under the following link.

http://actionbarsherlock.com 

The second option is to use the ActionBarCompat library from the Android support library v7, which supports the action bar as of Android 2.1. See the following link to setup the support library v7 in your project: Setting up the support library.

This section focuses on the description of using the action bar without the Open Source or support library. You can easily port your application to an earlier API version using one of the different libraries.

Entries in the action bar are typically called actions. While it is possible to create entries in the action bar via code, it is typically defined in an XML resource file.

Each menu definition is contained in a separate file in the res/menu folder. The Android tooling automatically creates a reference to this file in the R file, so that the menu resource can be accessed.

An activity adds entries to the action bar in its onCreateOptionsMenu() method.

The showAsAction attribute allows you to define how the action is displayed. For example, the ifRoom attribute defines that the action is only displayed in the action bar if there is sufficient screen space available.

<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@+id/action_refresh"
        android:orderInCategory="100"
        android:showAsAction="always"
        android:icon="@drawable/ic_action_refresh"
        android:title="Refresh"/>
    <item
        android:id="@+id/action_settings"
        android:title="Settings">
    </item>

</menu> 

The MenuInflator class allows to inflate actions defined in an XML file and adds them to the action bar.MenuInflator can get accessed via the getMenuInflator() method from your activity. The following example code demonstrates the creation of actions.

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

If an action is selected, the onOptionsItemSelected() method in the corresponding activity is called. It receives the selected action as parameter. Based on this information, you can decide what to do. The usage of this method is demonstrated in the following code snippet.

@Override
  public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    // action with ID action_refresh was selected
    case R.id.action_refresh:
      Toast.makeText(this, "Refresh selected", Toast.LENGTH_SHORT)
          .show();
      break;
    // action with ID action_settings was selected
    case R.id.action_settings:
      Toast.makeText(this, "Settings selected", Toast.LENGTH_SHORT)
          .show();
      break;
    default:
      break;
    }

    return true;
  } 

To search for a menu item in a menu you can use the findItem() method of the Menu class. This method allows to search by id.

The onCreateOptionsMenu() method is only called once. If you want to change the menu later, you have to call theinvalidateOptionsMenu() method. Afterwards this onCreateOptionsMenu() method is called again.

You can change the visibility of the action bar at runtime. The following code demonstrates that.

ActionBar actionBar = getActionBar();
actionBar.hide();
// more stuff here...
actionBar.show(); 

You can also change the text which is displayed alongside the application icon at runtime. The following example shows that.

ActionBar actionBar = getActionBar();
actionBar.setSubtitle("mytest");
actionBar.setTitle("vogella.com"); 

You also add a Drawable to the action bar as background via the ActionBar.setBackgroundDrawable() method.

The action bar scales the image. Therefore it is best practice to provide a scalable drawable , e.g., a 9-patch or XML drawable.

You can also dim the software navigation button in your Android application to have more space available. If the user touches the button of the screen, the navigation button is automatically shown again.

Dimming the navigation buttons is demonstrated by the following code snippet.

getWindow().
  getDecorView().
  setSystemUiVisibility(View.SYSTEM_UI_FLAG_HIDE_NAVIGATION); 

The following screenshots show an application with and without the navigation buttons.

As of Android 4.4 (API 19) you can put your application into full screen mode. The first time this happens the system displays the user the info that he can restore the system bars with a downward swipe along the region where the system bars normally appear.

For example the following method also to put an activity into full screen mode.

// This method hides the system bars and resize the content
  private void hideSystemUI() {
    getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
            | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION // hide nav bar
            | View.SYSTEM_UI_FLAG_FULLSCREEN // hide status bar
            // remove the following flag for version < API 19
            | View.SYSTEM_UI_FLAG_IMMERSIVE); 
  } 

You can define that the action bar should be automatically split by the system if not enough space is available.

You can activate this via the android:uiOptions="SplitActionBarWhenNarrow" parameter in the declaration of your application activity in the AndroidManifest.xml file.

You can also add a custom view to the action bar, for example, a button or a text field.

For this you use the setCustomView method of the ActionView class. You also have to enable the display of custom views via the setDisplayOptions() method by passing in the ActionBar.DISPLAY_SHOW_CUSTOM flag.

For example, you can define a layout file which contains a EditText element.

<?xml version="1.0" encoding="utf-8"?>
<EditText xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/searchfield"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:inputType="textFilter" >

</EditText> 

This layout can be assigned in an activity to the action bar via the following code. The example code also attaches a listener to the custom view.

package com.vogella.android.actionbar.customviews;

import android.app.ActionBar;
import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TextView.OnEditorActionListener;
import android.widget.Toast;

public class MainActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ActionBar actionBar = getActionBar();
    // add the custom view to the action bar
    actionBar.setCustomView(R.layout.actionbar_view);
    EditText search = (EditText) actionBar.getCustomView().findViewById(R.id.searchfield);
    search.setOnEditorActionListener(new OnEditorActionListener() {

      @Override
      public boolean onEditorAction(TextView v, int actionId,
          KeyEvent event) {
        Toast.makeText(MainActivity.this, "Search triggered",
            Toast.LENGTH_LONG).show();
        return false;
      }
    });
    actionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM
        | ActionBar.DISPLAY_SHOW_HOME);
  }

} 

A contextual action mode activates a temporary action bar that overlays the application action bar for the duration of a particular sub-task.

The contextual action mode is typically activated by selecting an item or by long clicking on it.

To implement this, call the startActionMode() method on a view or on your activity. This method gets anActionMode.Callback object which is responsible for the life cycle of the contextual action bar.

You could also assign a context menu to a view via the registerForContextMenu(view) method. A context menu is also activated if the user "long presses" the view. The onCreateContextMenu() method is called every time a context menu is activated as the context menu is discarded after its usage. You should prefer the contextual action mode over the usage of context menus.

An action view is a widget that appears in the action bar as a substitute for an action item's button. You can, for example, use this feature to replace an action item with a ProgressBar view. An action view for an action can be defined via the android:actionLayout or android:actionViewClass attribute to specify either a layout resource or widget class to use.

This replacement is depicted in the following screenshots.

The following activity replaces the icon at runtime with an action view which contains a ProgressBar view.

package com.vogella.android.actionbar.progress;

import android.app.ActionBar;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends Activity {

  private MenuItem menuItem;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ActionBar actionBar = getActionBar();
    actionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_HOME
        | ActionBar.DISPLAY_SHOW_TITLE | ActionBar.DISPLAY_SHOW_CUSTOM);
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  }

  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    case R.id.menu_load:
      menuItem = item;
      menuItem.setActionView(R.layout.progressbar);
      menuItem.expandActionView();
      TestTask task = new TestTask();
      task.execute("test");
      break;
    default:
      break;
    }
    return true;
  }

  private class TestTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {
      // Simulate something long running
      try {
        Thread.sleep(2000);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      return null;
    }

    @Override
    protected void onPostExecute(String result) {
      menuItem.collapseActionView();
      menuItem.setActionView(null);
    }
  };
} 

The following code shows the layout used for the action view.

<?xml version="1.0" encoding="utf-8"?>
<ProgressBar xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/progressBar2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

</ProgressBar> 

The following code shows the XML files for the menu.

<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@+id/menu_settings"
        android:orderInCategory="100"
        android:showAsAction="always"
        android:title="Settings"
        />

    <item
        android:id="@+id/menu_load"
        android:icon="@drawable/navigation_refresh"
        android:orderInCategory="200"
        android:showAsAction="always"
        android:title="Load"/>

</menu> 

An action provider defines rich menu interaction in a single component. It can generate action views, which are used in the action bar, dynamically populate sub-menus of an action and handle default action invocations.

The base class for an action provider is the ActionProvider class.

Currently the Android platform provides two action providers: the MediaRouteActionProvider and theShareActionProvider.

The following demonstrates the usage of the ShareActionProvider. This action provider allows you to grab selected content from applications which have registered the Intent.ACTION_SEND intent.

To use ShareActionProvider, you have to define a special menu entry for it and assign an intent which contains the sharing data to it.

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >

   <item android:id="@+id/menu_share"
          android:title="Share"
          android:showAsAction="ifRoom"
          android:actionProviderClass="android.widget.ShareActionProvider" />
    <item
        android:id="@+id/item1"
        android:showAsAction="ifRoom"
        android:title="More entries...">
    </item>

</menu> 

@Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);

    // Get the ActionProvider for later usage
    provider = (ShareActionProvider) menu.findItem(R.id.menu_share)
        .getActionProvider();
    return true;
  }

  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    case R.id.menu_share:
      doShare();
      break;
    default:
      break;
    }
    return true;  
  }

  public void doShare() {
    // populate the share intent with data
    Intent intent = new Intent(Intent.ACTION_SEND);
    intent.setType("text/plain");
    intent.putExtra(Intent.EXTRA_TEXT, "This is a message for you");
    provider.setShareIntent(intent);
  } 

The action bar shows an icon of your application. This is called the home icon. You can assign an action to this icon. The recommendation is to return to the main activity in your program if the user selects this icon.

If the action is selected, the onOptionsItemSelected() method is called with an action which has theandroid.R.id.home ID.

Before Android 4.1, you had to use the android.R.id.home ID in the onOptionMenuItemSelected() method and enable the selection of the home button. This is demonstrated by the following code in which the SecondActivity activity defines the MainActivity as home.

package com.vogella.android.actionbar.homebutton;

import android.os.Bundle;
import android.app.ActionBar;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuItem;

public class SecondActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // enable the home button
    ActionBar actionBar = getActionBar();
    actionBar.setHomeButtonEnabled(true);
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  }

  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    case android.R.id.home:
      Intent intent = new Intent(this, MainActivity.class);
      intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
      startActivity(intent);
      break;
      // Something else
    case R.id.action_settings:
      intent = new Intent(this, ThirdActivity.class);
      startActivity(intent);
    default:
      break;
    }
    return super.onOptionsItemSelected(item);
  }

} 

<activity
  android:name="SecondActivity"
  android:label="@string/app_name"
  android:parentActivityName="MainActivity" >
</activity> 

You can use the application icon also as Up button, e.g., to go to the parent activity of the current activity. The back button on the device always returns to the previous activity.

Both can be different, for example, if the user started the option to write an email from the home screen, the back button will return the user to the home screen while the Up button would return the user to the activity which shows an overview of all emails.

To enable the Up display, you can use the following code snippet in your activity.

actionBar.setDisplayUseLogoEnabled(false);
actionBar.setDisplayHomeAsUpEnabled(true); 

A relatively new navigation pattern is the navigation drawer. The navigation drawer is a panel that displays the navigation options on the left side of the screen. It is hidden by default, but can be displayed with a swipe from the left side to the right or if the user touches the app icon.

The usage of the navigation drawer in the Gmail application is depicted in the following screenshot.

The navigation drawer is part of the compatibility library v4. To use this navigation pattern, you create a layout with the android.support.v4.widget.DrawerLayout layout manager. This layout manager must contain only two child views. The first is the element for the main content and the second one the container for the drawer menu. The drawer menu is typically implemented with a ListView widget. Such a layout is demonstrated by the following snippet.

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <!-- The main content view -->
    <FrameLayout
        android:id="@+id/content_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    <!-- The navigation drawer -->
     <!-- should not be larger than 320 to show content -->
    <ListView android:id="@+id/left_drawer"
        android:layout_width="180dp"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:choiceMode="singleChoice"
        android:divider="@android:color/transparent"
        android:dividerHeight="0dp"
        android:background="#111"/>
</android.support.v4.widget.DrawerLayout> 

You can fill the ListView in your activity code and register a listener via the ListView.OnItemClickListern method on the list item. In this listener you can perform the navigation action. For example, you start a new activity or replace a fragment in your layout.

The following example demonstrates the usage of the navigation drawer. If you want to follow this example, create a new Android project and ensure that the support library is added to it.

Create a layout file called fragment_layout based on the following listing.

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

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:text="Placeholder Text"
        android:layout_gravity="center"
        android:textAppearance="?android:attr/textAppearanceLarge" />

</LinearLayout> 

Afterwards, create the OpertingSystemFragment class for the fragment.

package com.vogella.android.actionbar.navigationdrawer;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class OpertingSystemFragment extends Fragment {
  public static final String ARG_OS= "OS";
  private String string;
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
      Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_layout, null);
    TextView textView = (TextView) view.findViewById(R.id.textView1);
    textView.setText(string);
    return view;
  }
  @Override
  public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);  
  }
  @Override
  public void setArguments(Bundle args) {
    string = args.getString(ARG_OS);
  }
} 

Now add a few strings and a string array to your values/strings.xml file.

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">Navigationdrawer</string>
    <string name="action_settings">Settings</string>
    <string name="action_update">Update</string>
    <string name="drawer_open">Open Drawer</string>
    <string name="drawer_close">Close Drawer</string>
    <string name="hello_world">Hello world!</string>
    <string-array name="operating_systems">
        <item >Android</item>
        <item >iPhone</item>
        <item >Windows Mobile</item>
    </string-array>

</resources> 

Finally create the activity as follows.

package com.vogella.android.actionbar.navigationdrawer;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private String[] mPlanetTitles;
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;
  private ActionBarDrawerToggle mDrawerToggle;
  private CharSequence title;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        title = getActionBar().getTitle();
        mPlanetTitles = getResources().getStringArray(R.array.operating_systems);
        System.out.println(mPlanetTitles.length);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.left_drawer);

        // Set the adapter for the list view
        mDrawerList.setAdapter(new ArrayAdapter<String>(this,
                R.layout.drawer_item,R.id.content, mPlanetTitles));
        // Set the list's click listener
        mDrawerList.setOnItemClickListener(new DrawerItemClickListener());
        
        mDrawerToggle = new ActionBarDrawerToggle(this,                  /* host Activity */
                mDrawerLayout,         /* DrawerLayout object */
                R.drawable.ic_drawer,  /* nav drawer icon to replace 'Up' caret */
                R.string.drawer_open,  /* "open drawer" description */
                R.string.drawer_close  /* "close drawer" description */) {

            
/** Called when a drawer has settled in a completely closed state. */
            public void onDrawerClosed(View view) {
                getActionBar().setTitle(title);
            }

            
/** Called when a drawer has settled in a completely open state. */
            public void onDrawerOpened(View drawerView) {
                getActionBar().setTitle("Open Drawer");
            }
        };

        // Set the drawer toggle as the DrawerListener
        mDrawerLayout.setDrawerListener(mDrawerToggle);

        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setHomeButtonEnabled(true);
        

    }
    
    private class DrawerItemClickListener implements ListView.OnItemClickListener {
        @Override
        public void onItemClick(AdapterView parent, View view, int position, long id) {
            selectItem(position);
        }
    }
    
    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        mDrawerToggle.onConfigurationChanged(newConfig);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
      getMenuInflater().inflate(R.menu.main, menu);
      return super.onCreateOptionsMenu(menu);
    }
    
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Pass the event to ActionBarDrawerToggle, if it returns
        // true, then it has handled the app icon touch event
        if (mDrawerToggle.onOptionsItemSelected(item)) {
          return true;
        }
        // Handle your other action bar items...
        switch (item.getItemId()) {
    case R.id.action_settings:
      Toast.makeText(this, "Settings selected", Toast.LENGTH_LONG).show();
      break;

    default:
      break;
    }
        return super.onOptionsItemSelected(item);
    }


    
/** Swaps fragments in the main content view */
    private void selectItem(int position) {
        // create a new fragment and specify the planet to show based on position
        Fragment fragment = new OpertingSystemFragment();
        Bundle args = new Bundle();
        args.putInt(OpertingSystemFragment.ARG_OS, position);
        fragment.setArguments(args);

        // Insert the fragment by replacing any existing fragment
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                       .replace(R.id.content_frame, fragment)
                       .commit();

        // Highlight the selected item, update the title, and close the drawer
        mDrawerList.setItemChecked(position, true);
        getActionBar().setTitle((mPlanetTitles[position]));
        mDrawerLayout.closeDrawer(mDrawerList);
    }

  
} 

This activity uses a navigation drawer icon based on the recommendations of Google. You find an icon set from Google under the following URL: Navigation Drawer Icons.

This should be sufficient to add the navigation drawer to your application.

Fragments can also be used in combination with the action bar for navigation. For this your main activity needs to implement a TabListener, which is responsible for moving between the tabs.

To add a new tab to the action bar, use the newTab() method.

The following code shows such an activity. It uses dummy activities to demonstrate the switch.

package com.vogella.android.actionbar.tabs;

import android.app.ActionBar;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MainActivity extends FragmentActivity implements
    ActionBar.TabListener {

  
/**
   * The serialization (saved instance state) Bundle key representing the
   * current tab position.
   */
  private static final String STATE_SELECTED_NAVIGATION_ITEM = "selected_navigation_item";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Set up the action bar to show tabs.
    final ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // for each of the sections in the app, add a tab to the action bar.
    actionBar.addTab(actionBar.newTab().setText(R.string.title_section1)
        .setTabListener(this));
    actionBar.addTab(actionBar.newTab().setText(R.string.title_section2)
        .setTabListener(this));
    actionBar.addTab(actionBar.newTab().setText(R.string.title_section3)
        .setTabListener(this));
  }

  @Override
  public void onRestoreInstanceState(Bundle savedInstanceState) {
    // Restore the previously serialized current tab position.
    if (savedInstanceState.containsKey(STATE_SELECTED_NAVIGATION_ITEM)) {
      getActionBar().setSelectedNavigationItem(savedInstanceState.getInt(STATE_SELECTED_NAVIGATION_ITEM));
    }
  }

  @Override
  public void onSaveInstanceState(Bundle outState) {
    // Serialize the current tab position.
    outState.putInt(STATE_SELECTED_NAVIGATION_ITEM, getActionBar()
        .getSelectedNavigationIndex());
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
  }

  @Override
  public void onTabSelected(ActionBar.Tab tab,
      FragmentTransaction fragmentTransaction) {
    // When the given tab is selected, show the tab contents in the
    // container view.
    Fragment fragment = new DummySectionFragment();
    Bundle args = new Bundle();
    args.putInt(DummySectionFragment.ARG_SECTION_NUMBER,
        tab.getPosition() + 1);
    fragment.setArguments(args);
    getFragmentManager().beginTransaction()
        .replace(R.id.container, fragment).commit();
  }

  @Override
  public void onTabUnselected(ActionBar.Tab tab,
      FragmentTransaction fragmentTransaction) {
  }

  @Override
  public void onTabReselected(ActionBar.Tab tab,
      FragmentTransaction fragmentTransaction) {
  }

  
/**
   * A dummy fragment representing a section of the app
   */
  public static class DummySectionFragment extends Fragment {
    public static final String ARG_SECTION_NUMBER = "placeholder_text";

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
      TextView textView = new TextView(getActivity());
      textView.setGravity(Gravity.CENTER);
      textView.setText(Integer.toString(getArguments().getInt(ARG_SECTION_NUMBER)));
      return textView;
    }
  }

} 

You can also use a spinner in the action bar. The following code demonstrates such an implementation.

package com.vogella.android.actionbar.spinner;

import android.app.ActionBar;
import android.app.Fragment;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class MainActivity extends FragmentActivity implements
    ActionBar.OnNavigationListener {

  
/**
   * The serialization (saved instance state) Bundle key representing the
   * current dropdown position.
   */
  private static final String STATE_SELECTED_NAVIGATION_ITEM = "selected_navigation_item";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Set up the action bar to show a dropdown list.
    final ActionBar actionBar = getActionBar();
    actionBar.setDisplayShowTitleEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);

    final String[] dropdownValues = getResources().getStringArray(R.array.dropdown);

    // Specify a SpinnerAdapter to populate the dropdown list.
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(actionBar.getThemedContext(),
        android.R.layout.simple_spinner_item, android.R.id.text1,
        dropdownValues);

    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

    // Set up the dropdown list navigation in the action bar.
    actionBar.setListNavigationCallbacks(adapter, this);

    // use getActionBar().getThemedContext() to ensure
    // that the text color is always appropriate for the action bar
    // background rather than the activity background.
  }

  @Override
  public void onRestoreInstanceState(Bundle savedInstanceState) {
    // Restore the previously serialized current dropdown position.
    if (savedInstanceState.containsKey(STATE_SELECTED_NAVIGATION_ITEM)) {
      getActionBar().setSelectedNavigationItem(savedInstanceState.getInt(STATE_SELECTED_NAVIGATION_ITEM));
    }
  }

  @Override
  public void onSaveInstanceState(Bundle outState) {
    // Serialize the current dropdown position.
    outState.putInt(STATE_SELECTED_NAVIGATION_ITEM, getActionBar()
        .getSelectedNavigationIndex());
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
  }

  @Override
  public boolean onNavigationItemSelected(int position, long id) {
    // When the given dropdown item is selected, show its contents in the
    // container view.
    Fragment fragment = new DummySectionFragment();
    Bundle args = new Bundle();
    args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
    fragment.setArguments(args);
    getFragmentManager().beginTransaction()
        .replace(R.id.container, fragment).commit();
    return true;
  }

  
/**
   * A dummy fragment
   */
  public static class DummySectionFragment extends Fragment {

    public static final String ARG_SECTION_NUMBER = "placeholder_text";

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
      TextView textView = new TextView(getActivity());
      textView.setGravity(Gravity.CENTER);
      textView.setText(Integer.toString(getArguments().getInt(ARG_SECTION_NUMBER)));
      return textView;
    }
  }

} 

While the navigation drawer is relatively new compared to the other options, it is pretty popular among users and Android applications. If in doubt which options to select, consider using the navigation drawer.

This chapter will demonstrate how to create actions in the action bar and react to the selection of the user.

It is based on the fragment tutorial which can be found under Android fragments tutorial. If you have already created this project, you can continue to reuse it. If not, the following describes the required setup to continue with this tutorial.

Continue to use the com.example.android.rssfeed project.

Use File → New → Other... → Android → Android Icon Set to create a refresh icon for your action bar. The wizard allows you to select which type of icons you want to create. Specify the name ic_refresh for the new icon and select a corresponding entry from the clipart.

http://developer.android.com/design/downloads/index.html 

Create a new XML resource called mainmenu.xml for your menu.

To create this XML file, select your project, right click on it and select File → New → Other... → Android → Android XML File.

Select the Menu option, enter mainmenu.xml as the filename and press the Finish button.

This creates a new menu file in the res/menu folder of your project.

Open the mainmenu.xml file and select the Layout tab of the Android editor.

Press the Add button and select the Item entry.

Enter an entry similar to the following screenshot.

Add a second action to your menu. Use Refresh as the title attribute and action_refresh as the ID attribute.

Add a second entry to the menu with the ID attribute set to @+id/action_settings and the Title attribute set toSetting. Set the android:showAsAction to never.

Use the XML editor to assign the @drawable/ic_action_refresh to the action_refresh action via its android:iconproperty. You created or downloaded this icon in Section 10.1, “Create an icon for the ActionBar”.

The resulting XML should look similar to the following listing.

<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@+id/action_refresh"
        android:orderInCategory="100"
        android:showAsAction="always"
        android:icon="@drawable/ic_action_refresh"
        android:title="Refresh"/>
    <item
        android:id="@+id/action_settings"
        android:title="Settings"
        android:showAsAction="never"
        >
    </item>

</menu> 

Change your RssfeedActivity class to the following code to use the new menu resource file.

package com.example.android.rssfeed;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class RssfeedActivity extends Activity implements
    MyListFragment.OnItemSelectedListener {
  // Unchanged
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_rssfeed);
  }
  
  //NEW
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.mainmenu, menu);
    return true;
  }
  
  //NEW
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    case R.id.action_refresh:
      Toast.makeText(this, "Action refresh selected", Toast.LENGTH_SHORT)
          .show();
      break;
    case R.id.action_settings:
      Toast.makeText(this, "Action Settings selected", Toast.LENGTH_SHORT)
          .show();
      break;

    default:
      break;
    }

    return true;
  }

  // Other methods which this class implements
} 

Run your application and validate that you can select both of your actions. Ensure that the correct info message is displayed if you select the different entries.

If you have a refresh button in your fragment layout, you can remove it, as the action is used for the refresh operation.