ActionBar for Xamarin.Android

When using TabActivity, the code to create the tab icons has no effect when run against the Android 4.0 framework. Although functionally it works as it did in versions of Android prior to 2.3, the TabActivity class itself has been deprecated in 4.0. A new way to create a tabbed interface has been introduced that uses the Action Bar, which we'll discuss next.

Action Bar Tabs

The Action Bar includes support for adding tabbed interfaces in Android 4.0. The following screenshot shows an example of such an interface.

To create tabs in the Action Bar, we first need to set its NavigationMode property to support tabs. In Android 4, an ActionBar property is available on the Activity class, which we can use to set the NavigationMode like this:

this.ActionBar.NavigationMode = ActionBarNavigationMode.Tabs;

Once this is done, we can create a tab by calling the NewTab method on the Action Bar. With this tab instance, we can call the SetText and SetIcon methods to set the tab's label text and icon; these calls are made in order in the code shown below:

var tab = this.ActionBar.NewTab ();
tab.SetText (tabText);
tab.SetIcon (Resource.Drawable.ic_tab_white);

Before we can add the tab however, we need to handle the TabSelected event. In this handler, we can create the content for the tab. Action Bar tabs are designed to work with Fragments, which are classes that represent a portion of the user interface in an Activity. For this example, the Fragment's view contains a single TextView, which we inflate in our Fragment subclass like this:

class SampleTabFragment: Fragment
{           
    public override View OnCreateView (LayoutInflater inflater,
        ViewGroup container, Bundle savedInstanceState)
    {
        base.OnCreateView (inflater, container, savedInstanceState);

        var view = inflater.Inflate (
            Resource.Layout.Tab, container, false);

        var sampleTextView =
            view.FindViewById<TextView> (Resource.Id.sampleTextView);            
        sampleTextView.Text = "sample fragment text";

        return view;
    }
}

The event argument passed in the TabSelected event is of type TabEventArgs, which includes a FragmentTransaction property that we can use to add the fragment as shown below:

tab.TabSelected += delegate(object sender, ActionBar.TabEventArgs e) {             
    e.FragmentTransaction.Add (Resource.Id.fragmentContainer,
        new SampleTabFragment ());
};

Finally, we can add the tab to the Action Bar by calling the AddTab method as shown in this code:

this.ActionBar.AddTab (tab);

For the complete example, see the HelloTabsICS project in the sample code for this document.

ShareActionProvider

The ShareActionProvider class enables a sharing action to take place from an Action Bar. It takes care of creating an action view with a list of apps that can handle a sharing Intent and keeps a history of the previously used applications for easy access to them later from the Action Bar. This allows applications to share data via a user experience that's consistent throughout Android.

Image Sharing Example

For example, below is a screenshot of an Action Bar with a menu item to share an image. When the user taps the menu item on the Action Bar, the ShareActionProvider loads the application to handle an Intent that is associated with the ShareActionProvider. In this example, the messaging application has been previously used, so it is presented on the Action Bar.

When the user clicks on the item in the Action Bar, the messaging app that contains the shared image is launched, as shown below:

Specifying the action Provider Class

To use the ShareActionProvider, set the android:actionProviderClass attribute on a menu item in the XML for the Action Bar's menu as follows:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:id="@+id/shareMenuItem"
      android:showAsAction="always"
      android:title="@string/sharePicture"
      android:actionProviderClass="android.widget.ShareActionProvider" />
</menu>

Inflating the Menu

To inflate the menu, we override OnCreateOptionsMenu in the Activity subclass. Once we have a reference to the menu, we can get the ShareActionProvider from the ActionProvider property of the menu item and then use the SetShareIntent method to set the ShareActionProvider's Intent, as shown below:

public override bool OnCreateOptionsMenu (IMenu menu)
{
    MenuInflater.Inflate (Resource.Menu.ActionBarMenu, menu);       

    var shareMenuItem = menu.FindItem (Resource.Id.shareMenuItem);           
    var shareActionProvider =
       (ShareActionProvider)shareMenuItem.ActionProvider;
    shareActionProvider.SetShareIntent (CreateIntent ());
}

Creating the Intent

The ShareActionProvider will use the Intent, passed to the SetShareIntent method in the above code, to launch the appropriate Activity. In this case we create an Intent to send an image by using the following code:

Intent CreateIntent ()
{  
    var sendPictureIntent = new Intent (Intent.ActionSend);
    sendPictureIntent.SetType ("image/*");
    var uri = Android.Net.Uri.FromFile (GetFileStreamPath ("monkey.png"));          
    sendPictureIntent.PutExtra (Intent.ExtraStream, uri);
    return sendPictureIntent;
}

The image in the code example above is included as an asset with the application and copied to a publicly accessible location when the Activity is created, so it will be accessible to other applications, such as the messaging app. The sample code that accompanies this article contains the full source of this example, illustrating its use.