Creating the View

Recall from the basic Screenlet creation tutorial that a View defines a Screenlet’s UI. To accommodate its list, a list Screenlet’s View is constructed a bit differently than that of a non-list Screenlet. To create a List Screenlet’s View, you’ll create the following components:

  1. Row Layout: the layout for each list row.
  2. Adapter Class: an Android adapter class that populates each list row with data.
  3. View Class: the class that controls the View. This class serves the same purpose in list Screenlets as it does in non-list Screenlets.
  4. Main Layout: the layout for the list as a whole. Note this is different from the row layout, which defines the UI for individual rows.

First, you’ll create the row layout.

Creating the Row Layout

Before constructing the rest of the View, you should first define the layout to use for each row in the list. For example, Bookmark List Screenlet needs to display a bookmark in each row. Its row layout (res/layout/bookmark_row.xml) is therefore a LinearLayout containing a single TextView that displays the bookmark’s URL:

<?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="wrap_content"
    android:orientation="vertical">

    <TextView
        android:id="@+id/bookmark_url"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

As you can see, this example is very simple. Row layouts, however, can be as simple or complex as you need them to be to display your content.

Next, you’ll create the adapter class.

Creating the Adapter Class

Android adapters fill a layout with content. In the example Bookmark List Screenlet, the layout is the row layout (bookmark_row.xml) and the content is each list item (a URL). To make list scrolling smooth, the adapter class should use an Android view holder. To make this easier, you can extend the list Screenlet framework’s BaseListAdapter class with your model class and view holder as type arguments. By extending BaseListAdapter, your adapter needs only two methods:

  • createViewHolder: instantiates the view holder
  • fillHolder: fills in the view holder for each row

Your view holder should also contain variables for any data each row needs to display. The view holder must assign these variables to the corresponding row layout elements, and set the appropriate data to them.

For example, Bookmark List Screenlet’s adapter class (BookmarkAdapter) extends BaseListAdapter with Bookmark and BookmarkAdapter.BookmarkViewHolder as type arguments. This class’s view holder is an inner class that extends BaseListAdapter’s view holder. Since Bookmark List Screenlet only needs to display a URL in each row, the view holder only needs one variable: url. The view holder’s constructor assigns the TextView from bookmark_row.xml to this variable. The bind method then sets the bookmark’s URL as the TextView’s text. The other methods in BookmarkAdapter leverage the view holder. The createViewHolder method instantiates BookmarkViewHolder. The fillHolder method calls the view holder’s bind method to set the bookmark’s URL as the url variable’s text:

public class BookmarkAdapter extends BaseListAdapter<Bookmark, BookmarkAdapter.BookmarkViewHolder> {

    public BookmarkAdapter(int layoutId, int progressLayoutId, BaseListAdapterListener listener) {
        super(layoutId, progressLayoutId, listener);
    }

    @NonNull
    @Override
    public BookmarkViewHolder createViewHolder(View view, BaseListAdapterListener listener) {
        return new BookmarkAdapter.BookmarkViewHolder(view, listener);
    }

    @Override
    protected void fillHolder(Bookmark entry, BookmarkViewHolder holder) {
        holder.bind(entry);
    }

    public class BookmarkViewHolder extends BaseListAdapter.ViewHolder {

        private final TextView url;

        public BookmarkViewHolder(View view, BaseListAdapterListener listener) {
            super(view, listener);

            url = (TextView) view.findViewById(R.id.bookmark_url);
        }

        public void bind(Bookmark entry) {
            url.setText(entry.getUrl());
        }
    }
}

Great! Your adapter class is finished. Next, you’ll create the View class.

Creating the View Class

Now that your adapter exists, you can create your list Screenlet’s View class. Recall from the basic Screenlet creation tutorial that the View class is the central hub of any Screenlet’s UI. It renders the UI, handles user interactions, and communicates with the Screenlet class. The list Screenlet framework provides most of this functionality for you via the BaseListScreenletView class. Your View class must extend this class to provide your row layout ID and an instance of your adapter. You’ll do this by overriding BaseListScreenletView’s getItemLayoutId and createListAdapter methods. Note that in many cases this is the only custom functionality your View class needs. If it needs more, you can provide it by creating new methods or overriding other BaseListScreenletView methods.

Create your View class by extending BaseListScreenletView with your model class, view holder, and adapter as type arguments. This is required for your View class to represent your model objects in a view holder, inside an adapter. For example, Bookmark List Screenlet’s View class (BookmarkListView) must represent Bookmark instances in a BookmarkViewHolder inside a BookmarkAdapter. The BookmarkListView class must therefore extend BaseListScreenletView parameterized with Bookmark, BookmarkAdapter.BookmarkViewHolder, and BookmarkAdapter. Besides overriding createListAdapter to return a BookmarkAdapter instance, the only other functionality that this View class needs to support is to get the layout for each row in the list. The overridden getItemLayoutId method does this by returning the row layout bookmark_row:

import android.content.Context;
import android.util.AttributeSet;

import com.liferay.mobile.screens.base.list.BaseListScreenletView;

public class BookmarkListView
    extends BaseListScreenletView<Bookmark, BookmarkAdapter.BookmarkViewHolder, BookmarkAdapter> {

    public BookmarkListView(Context context) {
        super(context);
    }

    public BookmarkListView(Context context, AttributeSet attributes) {
        super(context, attributes);
    }

    public BookmarkListView(Context context, AttributeSet attributes, int defaultStyle) {
        super(context, attributes, defaultStyle);
    }

    @Override
    protected BookmarkAdapter createListAdapter(int itemLayoutId, int itemProgressLayoutId) {
        return new BookmarkAdapter(itemLayoutId, itemProgressLayoutId, this);
    }

    @Override
    protected int getItemLayoutId() {
        return R.layout.bookmark_row;
    }
}

Next, you’ll create your View’s main layout.

Creating the View’s Main Layout

Although you already created a layout for your list rows, you must still create a layout to define the list as a whole. This layout must contain:

  • The View class’s fully qualified name as the layout’s first element.
  • An Android RecyclerView to let your app efficiently scroll through a potentially large list of items.
  • An Android ProgressBar to indicate progress when loading the list.

Apart from the View class and styling, this layout’s code is the same for all list Screenlets. For example, here’s Bookmark List Screenlet’s layout res/layout/list_bookmarks.xml:

<com.liferay.mobile.screens.listbookmark.BookmarkListView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/liferay_list_screenlet"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ProgressBar
        android:id="@+id/liferay_progress"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:visibility="gone"/>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/liferay_recycler_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:visibility="gone"/>
</com.liferay.mobile.screens.listbookmark.BookmarkListView>

Great job! Your View is finished. Next, you’ll create your Screenlet’s Interactor.

Creating the Model Class

Creating the Interactor

Creating the Screenlet Class

« Creating the Model ClassCreating the Interactor »
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