wearables/ui/lists.jd

page.title=Creating Lists

@jd:body

<div id="tb-wrapper">
<div id="tb">
<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#add-list">Add a List View</a></li>
  <li><a href="#layout-impl">Create a Layout Implementation for List Items</a></li>
  <li><a href="#layout-def">Create a Layout Definition for Items</a></li>
  <li><a href="#adapter">Create an Adapter to Populate the List</a></li>
  <li><a href="#adapter-listener">Associate the Adapter and Set a Click Listener</a></li>
</ol>
<h2>You should also read</h2>
<ul>
  <li><a href="{@docRoot}design/wear/index.html">Android Wear Design Principles</a></li>
</ul>
</div>
</div>


<p>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.</p>

<p>The Wearable UI Library includes the <code>WearableListView</code> class, which is a list
implementation optimized for wearable devices..</p>

<p class="note"><strong>Note:</strong> The <em>Notifications</em> sample in the Android SDK
demonstrates how to use <code>WearableListView</code> in your apps. This sample is located in
the <code>android-sdk/samples/android-20/wearable/Notifications</code> directory.</p>

<p>To create a list in your Android Wear apps:</p>

<ol>
<li>Add a <code>WearableListView</code> element to your activity's layout definition.</li>
<li>Create a custom layout implementation for your list items.</li>
<li>Use this implementation to create a layout definition file for your list items.</li>
<div style="float:right;margin-left:25px;width:215px;margin-top:-20px">
<img src="{@docRoot}wear/images/06_uilib.png" width="200" height="200" alt=""/>
<p class="img-caption" style="text-align:center"><strong>Figure 3:</strong>
A list view on Android Wear.</p>
</div>
<li>Create an adapter to populate the list.</li>
<li>Assign the adapter to the <code>WearableListView</code> element.</li>
</ol>

<p>These steps are described in detail in the following sections.</p>


<h2 id="add-list">Add a List View</h2>

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

<pre>
&lt;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">

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

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


<h2 id="layout-impl">Create a Layout Implementation for List Items</h2>

<p>In many cases, each list item consists of an icon and a description. The
<em>Notifications</em> sample from the Android SDK implements a custom layout that extends
{@link android.widget.LinearLayout} to incorporate these two elements inside each list item.
This layout also implements the methods in the <code>WearableListView.Item</code> interface
to animate the item's icon and fade the text in response to events from
<code>WearableListView</code> as the user scrolls through the list.</p>

<pre>
public class WearableListItemLayout extends LinearLayout
                                    implements WearableListView.Item {

    private final float mFadedTextAlpha;
    private final int mFadedCircleColor;
    private final int mChosenCircleColor;
    private ImageView mCircle;
    private float mScale;
    private TextView mName;

    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
    &#64;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);
    }

    // Provide scaling values for WearableListView animations
    &#64;Override
    public float getProximityMinValue() {
        return 1f;
    }

    &#64;Override
    public float getProximityMaxValue() {
        return 1.6f;
    }

    &#64;Override
    public float getCurrentProximityValue() {
        return mScale;
    }

    // Scale the icon for WearableListView animations
    &#64;Override
    public void setScalingAnimatorValue(float scale) {
        mScale = scale;
        mCircle.setScaleX(scale);
        mCircle.setScaleY(scale);
    }

    // Change color of the icon, remove fading from the text
    &#64;Override
    public void onScaleUpStart() {
        mName.setAlpha(1f);
        ((GradientDrawable) mCircle.getDrawable()).setColor(mChosenCircleColor);
    }

    // Change the color of the icon, fade the text
    &#64;Override
    public void onScaleDownStart() {
        ((GradientDrawable) mCircle.getDrawable()).setColor(mFadedCircleColor);
        mName.setAlpha(mFadedTextAlpha);
    }
}
</pre>


<h2 id="layout-def">Create a Layout Definition for Items</h2>

<p>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:</p>

<p class="code-caption">res/layout/list_item.xml</p>

<pre>
&lt;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">
    &lt;ImageView
        android:id="@+id/circle"
        android:layout_height="20dp"
        android:layout_margin="16dp"
        android:layout_width="20dp"
        android:src="@drawable/wl_circle"/>
    &lt;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"/>
&lt;/com.example.android.support.wearable.notifications.WearableListItemLayout>
</pre>


<h2 id="adapter">Create an Adapter to Populate the List</h2>

<p>The adapter populates the <code>WearableListView</code> with content. The following simple
adapter populates the list with elements based on an array of strings:</p>

<pre>
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)
    &#64;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)
    &#64;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)
    &#64;Override
    public int getItemCount() {
        return mDataset.length;
    }
}
</pre>


<h2 id="adapter-listener">Associate the Adapter and Set a Click Listener</h2>

<p>In your activity, obtain a reference to the <code>WearableListView</code> 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.</p>

<pre>
public class WearActivity extends Activity
                          implements WearableListView.ClickListener {

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

    &#64;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
    &#64;Override
    public void onClick(WearableListView.ViewHolder v) {
        Integer tag = (Integer) v.itemView.getTag();
        // use this data to complete some action ...
    }

    &#64;Override
    public void onTopEmptyRegionClick() {
    }
}
</pre>