Creating Lists

Lists let users select an item from a set of choices easily on wearable devices. This lesson shows you how to create lists in your Android Wear apps.

The Wearable UI Library includes the WearableListView class, which is a list implementation optimized for wearable devices.

To create a list in your Android Wear apps:

1. Add a WearableListView element to your activity's layout definition.
2. Create a custom layout implementation for your list items.
3. Use this implementation to create a layout definition file for your list items.
4. Create an adapter to populate the list.
5. Assign the adapter to the WearableListView element.

Figure 1. A list view on Android Wear.

These steps are described in detail in the following sections.

Add a List View

The following layout adds a list view to an activity using a <BoxInsetLayout> element, so the list is displayed properly on both round and square devices:

<android.support.wearable.view.BoxInsetLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="@drawable/robot_background"
    android:layout_height="match_parent"
    android:layout_width="match_parent">

    <FrameLayout
        android:id="@+id/frame_layout"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        app:layout_box="left|bottom|right">

        <android.support.wearable.view.WearableListView
            android:id="@+id/wearable_list"
            android:layout_height="match_parent"
            android:layout_width="match_parent">
        </android.support.wearable.view.WearableListView>
    </FrameLayout>
</android.support.wearable.view.BoxInsetLayout>

Create a Layout Implementation for List Items

In many cases, each list item consists of an icon and a description. The Notifications sample implements a custom layout that extends LinearLayout to incorporate these two elements inside each list item. This layout also implements the methods in the WearableListView.OnCenterProximityListener interface to change the color of the item's icon and fade the text in response to events from the WearableListView element as the user scrolls through the list.

public class WearableListItemLayout extends LinearLayout
             implements WearableListView.OnCenterProximityListener {

    private ImageView mCircle;
    private TextView mName;

    private final float mFadedTextAlpha;
    private final int mFadedCircleColor;
    private final int mChosenCircleColor;

    public WearableListItemLayout(Context context) {
        this(context, null);
    }

    public WearableListItemLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public WearableListItemLayout(Context context, AttributeSet attrs,
                                  int defStyle) {
        super(context, attrs, defStyle);

        mFadedTextAlpha = getResources()
                         .getInteger(R.integer.action_text_faded_alpha) / 100f;
        mFadedCircleColor = getResources().getColor(R.color.grey);
        mChosenCircleColor = getResources().getColor(R.color.blue);
    }

    // Get references to the icon and text in the item layout definition
    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        // These are defined in the layout file for list items
        // (see next section)
        mCircle = (ImageView) findViewById(R.id.circle);
        mName = (TextView) findViewById(R.id.name);
    }

    @Override
    public void onCenterPosition(boolean animate) {
        mName.setAlpha(1f);
        ((GradientDrawable) mCircle.getDrawable()).setColor(mChosenCircleColor);
    }

    @Override
    public void onNonCenterPosition(boolean animate) {
        ((GradientDrawable) mCircle.getDrawable()).setColor(mFadedCircleColor);
        mName.setAlpha(mFadedTextAlpha);
    }
}

You can also create animator objects to enlarge the icon of the center item in the list. You can use the onCenterPosition() and onNonCenterPosition() callback methods in the WearableListView.OnCenterProximityListener interface to manage your animators. For more information about animators, see Animating with ObjectAnimator.

Create a Layout Definition for Items

After you implement a custom layout for list items, you provide a layout definition file that specifies the layout parameters of each of the components inside a list item. The following layout definition uses the custom layout implementation from the previous section and defines an icon and a text view whose IDs match those in the layout implementation class:

res/layout/list_item.xml

<com.example.android.support.wearable.notifications.WearableListItemLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:gravity="center_vertical"
    android:layout_width="match_parent"
    android:layout_height="80dp">
    <ImageView
        android:id="@+id/circle"
        android:layout_height="20dp"
        android:layout_margin="16dp"
        android:layout_width="20dp"
        android:src="@drawable/wl_circle"/>
    <TextView
        android:id="@+id/name"
        android:gravity="center_vertical|left"
        android:layout_width="wrap_content"
        android:layout_marginRight="16dp"
        android:layout_height="match_parent"
        android:fontFamily="sans-serif-condensed-light"
        android:lineSpacingExtra="-4sp"
        android:textColor="@color/text_color"
        android:textSize="16sp"/>
</com.example.android.support.wearable.notifications.WearableListItemLayout>

Create an Adapter to Populate the List

The adapter populates the WearableListView.OnCenterProximityListener element with content. The following simple adapter populates the list with elements based on an array of strings:

private static final class Adapter extends WearableListView.Adapter {
    private String[] mDataset;
    private final Context mContext;
    private final LayoutInflater mInflater;

    // Provide a suitable constructor (depends on the kind of dataset)
    public Adapter(Context context, String[] dataset) {
        mContext = context;
        mInflater = LayoutInflater.from(context);
        mDataset = dataset;
    }

    // Provide a reference to the type of views you're using
    public static class ItemViewHolder extends WearableListView.ViewHolder {
        private TextView textView;
        public ItemViewHolder(View itemView) {
            super(itemView);
            // find the text view within the custom item's layout
            textView = (TextView) itemView.findViewById(R.id.name);
        }
    }

    // Create new views for list items
    // (invoked by the WearableListView's layout manager)
    @Override
    public WearableListView.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                          int viewType) {
        // Inflate our custom layout for list items
        return new ItemViewHolder(mInflater.inflate(R.layout.list_item, null));
    }

    // Replace the contents of a list item
    // Instead of creating new views, the list tries to recycle existing ones
    // (invoked by the WearableListView's layout manager)
    @Override
    public void onBindViewHolder(WearableListView.ViewHolder holder,
                                 int position) {
        // retrieve the text view
        ItemViewHolder itemHolder = (ItemViewHolder) holder;
        TextView view = itemHolder.textView;
        // replace text contents
        view.setText(mDataset[position]);
        // replace list item's metadata
        holder.itemView.setTag(position);
    }

    // Return the size of your dataset
    // (invoked by the WearableListView's layout manager)
    @Override
    public int getItemCount() {
        return mDataset.length;
    }
}

Associate the Adapter and Set a Click Listener

In your activity, obtain a reference to the WearableListView.OnCenterProximityListener element from your layout, assign an instance of the adapter to populate the list, and set a click listener to complete an action when the user selects a particular list item.

public class WearActivity extends Activity
                          implements WearableListView.ClickListener {

    // Sample dataset for the list
    String[] elements = { "List Item 1", "List Item 2", ... };

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

        // Get the list component from the layout of the activity
        WearableListView listView =
            (WearableListView) findViewById(R.id.wearable_list);

        // Assign an adapter to the list
        listView.setAdapter(new Adapter(this, elements));

        // Set a click listener
        listView.setClickListener(this);
    }

    // WearableListView click listener
    @Override
    public void onClick(WearableListView.ViewHolder v) {
        Integer tag = (Integer) v.itemView.getTag();
        // use this data to complete some action ...
    }

    @Override
    public void onTopEmptyRegionClick() {
    }
}