Using Guestbook List Screenlet

The steps for using Guestbook List Screenlet are the same as those for using any Screenlet:

  1. Insert the Screenlet’s XML in the activity or fragment layout you want the Screenlet to appear in.

  2. Implement the Screenlet’s listener in the activity or fragment class.

Recall that you used these steps to insert Login Screenlet in MainActivity. First, you’ll insert Guestbook List Screenlet’s XML in GuestbooksActivity’s layout.

Inserting the Screenlet XML in the Layout

Recall that activity_guestbooks.xml defines GuestbooksActivity’s UI. Also recall that the NavigationView in activity_guestbooks.xml defines the navigation drawer.

To put Guestbook List Screenlet in the drawer, you must insert the Screenlet’s XML in the NavigationView. You must also remove the placeholder content from the NavigationView. To do these things, replace the NavigationView in activity_guestbooks.xml with this code:




Compared to the NavigationView it replaced, this NavigationView contains Guestbook List Screenlet’s XML and lacks the app:menu attribute. Recall that this attribute pointed to the menu resource file that creates the drawer’s items. Since the Screenlet now handles the drawer’s items (the guestbooks), you don’t need app:menu or the menu resource file. Delete the menu resource file res/menu/activity_guestbooks_drawer.xml. You also don’t need the drawable resources that Android Studio created for the navigation drawer’s placeholder content. Delete res/values/drawables.xml, and each of the ic_menu_*.xml files in res/drawable.

Returning your attention to activity_guestbooks.xml, note that Guestbook List Screenlet’s XML strongly resembles Login Screenlet’s XML. Both contain an android:id value that you can use in the activity to get a reference to the Screenlet. Both also use a layoutId attribute to specify the Screenlet’s View. Guestbook List Screenlet’s XML, however, differs by using the android:paddingTop attribute. This attribute’s value, @dimen/nav_header_height, pads the top of the Screenlet by the height of the navigation drawer’s header section. This prevents the Screenlet and drawer header from overlapping.

Great! Next, you’ll implement the Screenlet’s listener interface in GuestbooksActivity.

Implementing the Screenlet’s Listener

To use a Screenlet, you must implement its listener methods in the class of the activity or fragment where you want the Screenlet to appear. How you implement these methods depends on how you want the Screenlet to function in your app. For example, when you used Login Screenlet you implemented LoginListener in MainActivity. You implemented this listener’s onLoginSuccess and onLoginFailure methods to display a message to the user. You then changed the onLoginSuccess implementation to navigate from MainActivity to GuestbooksActivity. Since these methods are void, however, you could have left them empty. Obviously this wouldn’t have made for a very useful app, but it highlights an important point: Screenlet listener methods let the app developer choose how to respond to the Screenlet’s events. By implementing these methods, app developers can therefore control how the Screenlet functions with their app.

Before implementing Guestbook List Screenlet’s listener, however, you should add a method that the listener methods can use to help display a guestbook and its entries. You might now be thinking, “I thought you said Screenlets contain their own UIs? Why does the activity need special methods for displaying the Screenlets’ entities?” Although a list Screenlet’s UI displays the list of entities, the rest of the app’s UI must still account for that list. Consider the action bar, for example. List Screenlets don’t include an action bar, but you should still change the action bar’s contents to reflect what’s on the screen. When a guestbook is selected in Guestbook List Screenlet, the action bar should display that guestbook’s name. You can accomplish this by calling a method that takes a GuestbookModel and sets that guestbook’s name as the action bar’s title.

Follow these steps to add this method and implement the listener:

  1. Add this showEntries method to GuestbooksActivity:

    public void showEntries(GuestbookModel guestbook) {

    This requires you to import This method is called showEntries because you’ll also use it to display the guestbook’s entries via Entry List Screenlet (you’ll add this code later). You’ll call this method in the listener methods you’ll implement to process a guestbook selection.

  2. Recall that Guestbook List Screenlet doesn’t need any custom listener methods. It can use the listener methods defined in the list Screenlet framework’s BaseListListener interface. Change GuestbooksActivity’s class declaration to implement BaseListListener<GuestbookModel>. The class declaration should now look like this:

    public class GuestbooksActivity extends AppCompatActivity implements 
        BaseListListener<GuestbookModel> {...

    This requires you to import

  3. To implement BaseListListener, you must implement the following methods:

    • onListPageFailed(int startRow, Exception e): Called when the server call to retrieve a page of items fails. This method’s arguments include the Exception generated when the server call failed. Implement this method to show the user a toast message containing an error:

        public void onListPageFailed(int startRow, Exception e) {
            Toast.makeText(this, "Page request failed", Toast.LENGTH_LONG).show();

      This requires you to import android.widget.Toast.

    • onListPageReceived(int startRow, int endRow, List<E> entries, int rowCount): Called when the server call to retrieve a page of items succeeds. Note that this method’s arguments include the list of objects retrieved from the server (entries), and the page’s start row (startRow), and end row (endRow). Recall that by default, you want the activity to display the first guestbook’s entries. You’ll use this method to do so because it receives the guestbooks from the server. Note that because startRow and endRow change for each page, a startRow of 0 corresponds to the first guestbook on the first page. Use an if statement to select this guestbook, and then call showEntries:

        public void onListPageReceived(int startRow, int endRow, List<GuestbookModel> guestbooks, 
            int rowCount) {
            if (startRow == 0) {

      This requires you to import java.util.List.

    • onListItemSelected(E element, View view): Called when the user selects an item in the list. This method’s arguments include the selected list item (element). To process the guestbook’s selection, call showEntries in this method. Also, close the navigation drawer following the showEntries call:

        public void onListItemSelected(GuestbookModel guestbook, View view) {
  4. Because BaseListListener extends the BaseCacheListener interface, the activity must also implement BaseCacheListener’s error method. This method lets you respond to an error alongside the user action that caused it. In this app, you don’t need to do anything in this method, so you can leave its contents empty:

    public void error(Exception e, String userAction) {
  5. Now that you’ve implemented the listener methods, you must set GuestbooksActivity as the listener. This is where the guestbooklist_screenlet ID that you set in the Screenlet’s XML comes in handy. Add the following code to the end of the activity’s onCreate method:

    GuestbookListScreenlet screenlet = 
        (GuestbookListScreenlet) findViewById(;

    This requires you to import

    This code first uses the ID guestbooklist_screenlet to get a reference to GuestbookListScreenlet. It then sets this GuestbooksActivity instance as the Screenlet’s listener.

Great! That’s it! Your app’s GuestbooksActivity now contains Guestbook List Screenlet. You’re almost ready to use Entry List Screenlet. Before you do so, however, you must create a fragment to put it in. You’ll do this next.

« Preparing GuestbooksActivity for Guestbook List ScreenletCreating a Fragment for Entry List Screenlet »
Este artigo foi útil?
Utilizadores que acharam útil: 0 de 0