Creating a Fragment for Entry List Screenlet

Using a fragment for Entry List Screenlet lets you swap out part of GuestbookActivity’s contents without recreating the entire activity from scratch each time a guestbook is selected. Your app doesn’t currently have any fragments, though. In this step, you’ll create a fragment and then add it to GuestbooksActivity. When you finish, you’ll be ready to use Entry List Screenlet in this fragment.

Creating the Fragment

Follow these steps to create the fragment:

1. To create the fragment, right click the com.liferay.docs.liferayguestbook package and select New → Fragment → Fragment (Blank). In the wizard, check only the box to create the layout XML, name the fragment EntriesFragment, and then click Finish. The following screenshot illustrates this:

   

   Figure 1: Create a new blank fragment for the entries.

   This creates the EntriesFragment class and its layout file fragment_entries.xml.

2. Replace the class’s contents with this code:

   package com.liferay.docs.liferayguestbook;
   
   import android.os.Bundle;
   import android.support.v4.app.Fragment;
   import android.view.LayoutInflater;
   import android.view.View;
   import android.view.ViewGroup;
   
   public class EntriesFragment extends Fragment {
   
       public static EntriesFragment newInstance(long guestbookId) {
           EntriesFragment entriesFragment = new EntriesFragment();
           Bundle args = new Bundle();
           args.putLong("guestbookId", guestbookId);
           entriesFragment.setArguments(args);
   
           return entriesFragment;
       }
   
       @Override
       public View onCreateView(LayoutInflater inflater, ViewGroup container,
                            Bundle savedInstanceState) {
           // Inflate the layout for this fragment
           View view = inflater.inflate(R.layout.fragment_entries, container, false);
           long guestbookId = getArguments().getLong("guestbookId");
   
           return view;
       }
   
   }
   

   If you have experience with Android fragments, then you’re likely familiar with the static newInstance method. In short, using such a method instead of an empty constructor lets you create the fragment and initialize its data in one step. This makes it easier to create and restore the fragment. Click here for more information.

   Since this fragment will contain Entry List Screenlet, its data must include the guestbook ID the Screenlet retrieves entries from (guestbookId). Also, the onCreateView method uses the bundle arguments set in newInstance to retrieve the guestbookId. For now, you don’t have to do anything with the guestbookId in onCreateView. You’ll use this variable when you add the Screenlet to the fragment.

Next, you’ll add this fragment to GuestbooksActivity.

Adding the Fragment to GuestbooksActivity

Now that EntriesFragment exists, you can add it to GuestbooksActivity. To do this, you must put an Android fragment container in the layout where you want the fragment. For more information, see Android’s documentation on adding fragments at runtime. Since you want Entry List Screenlet to appear in GuestbooksActivity, your first thought might be to put the fragment container directly in activity_guestbooks.xml. Don’t do this. Recall that Android Studio’s Navigation Drawer Activity template created the layout content_guestbooks.xml to hold the activity’s main body content. You’ll add the fragment container to this layout, then write the code in GuestbooksActivity that displays the fragment.

Follow these steps to add the fragment to GuestbooksActivity:

1. Open content_guestbooks.xml and place the following fragment container inside the ConstraintLayout. This fragment container should be the only other element inside the ConstraintLayout:

   <FrameLayout
       android:id="@+id/fragment_container"
       android:layout_width="match_parent"
       android:layout_height="match_parent" />
   

2. Next, you must write the GuestbooksActivity code that displays the fragment when a guestbook is selected in Guestbook List Screenlet. You’ll do this with an Android fragment transaction. Recall that you created GuestbooksActivity’s showEntries method to process a list item selection in Guestbook List Screenlet. All showEntries does right now is set the action bar’s title to the selected guestbook’s name. You’ll add the fragment transaction to showEntries, so a guestbook selection also shows that guestbook’s entries. Replace the showEntries method in GuestbooksActivity with this code:

   public void showEntries(GuestbookModel guestbook) {
       actionBar.setTitle(guestbook.getName());
   
       EntriesFragment entriesFragment = EntriesFragment.newInstance(guestbook.getGuestbookId());
       FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
       transaction.replace(R.id.fragment_container, entriesFragment);
       transaction.commit();
   }
   

   This requires that you import android.support.v4.app.FragmentTransaction.

   This method’s actionBar.setTitle call is the same as before. Only the fragment code is new. In it, you first use newInstance to create a new EntriesFragment instance with the selected guestbook’s ID. A fragment transaction then adds this fragment to the fragment container.

Fantastic! Now you have a fragment to put Entry List Screenlet in, and the code that displays this fragment in GuestbooksActivity. Next, you’ll put Entry List Screenlet in the fragment.