page.title=Creating Interactive Watch Faces

@jd:body

<div id="tb-wrapper">
<div id="tb">
<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#Construct">Construct an Interactive Watch Face</a></li>
  <li><a href="#Handle">Handle Gestures</a></li>
</ol>
<h2>You should also read</h2>
<ul>
  <li><a href="{@docRoot}design/wear/watchfaces.html">Watch Faces for Android Wear</a></li>
</ul>
<h2>Related Samples</h2>
  <ul>
    <li><a href="{@docRoot}samples/WatchFace/index.html">WatchFace</a></li>
  </ul>
</div>
</div>

<p>Your watch's display is more than just a pretty face: Users can  interact with it.
For example, a user might tap the watch face to learn what song is currently playing, or
to see the day's agenda. Android Wear allows Android Wear watch faces to accept
the single-tap gesture at a given location on the watch face, as long as there's not another
UI element that also responds to that gesture.

<p>This lesson teaches you how to implement an interactive watch face by first constructing the
watch face style, and then implementing gesture handling.</p>

<p class="note"><strong>Note:</strong> Before beginning development work on your interactive watch
face, you should be sure to read the <a href="{@docRoot}design/wear/watchfaces.html">Watch Faces for
Android Wear</a> design guide.

<h2 id="Construct">Handling Tap Events</h2>

<p>When constructing an interactive watch-face style, the first thing the app must do is tell the
system that the watch face receives <a href="{@docRoot}design/wear/watchfaces.html#ag">tap events</a>.
The following example shows how to do this:

<pre>
setWatchFaceStyle(new WatchFaceStyle.Builder(mService)
    .setAcceptsTapEvents(true)
    // other style customizations
    .build());
</pre>

<p>When the system detects a tap on the watch face, it triggers the
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.Engine.html#onTapCommand(int, int, int, long)">
{@code WatchFaceService.Engine.onTapCommand()}</a> method. Override this method in your
implementation of
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.Engine.html">
{@code WatchFaceService.Engine}</a>to initiate the action you wish to perform, such
as showing a detailed step count or changing the theme of the watch face. The code snippet
in <a href="#Handle">Handle Gestures</a> shows an example of such an
implementation.</p>

<h2 id="Handle">Handle Gestures</h2>

<p> To provide a consistent user experience, the system
reserves gestures such as drag and long-press for system UI elements.
Therefore, the system does not send raw touch events to the watch face. Instead, the system forwards specific commands to the
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.Engine.html#onTapCommand(int, int, int, long)">
onTapCommand()</a> method.

<p>The system sends the first command,
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.html#TAP_TYPE_TOUCH">
{@code TAP_TYPE_TOUCH}</a>, when the user initially touches the
screen. This event lets you provide visual feedback to the user on touch.  Your app should not
launch a UI when this event triggers. Launching a UI prevents drag events from opening the app
launcher, settings shade, and notifications stream.</p>

<p>Before sending the next command, the system judges whether the contact is a single tap, which is
<a href="{@docRoot}design/wear/watchfaces.html#ag">the only gesture allowed</a>. If the user
immediately lifts their finger, the system determines that a single tap took place, and forwards
a
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.html#TAP_TYPE_TAP"</a>
{@code TAP_TYPE_TAP}</a> event. If the user does not immediately lift their finger, the system
forwards a
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.html#TAP_TYPE_TOUCH_CANCEL"</a>
{@code TAP_TYPE_TOUCH_CANCEL}</a> event. Once the user has triggered a
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.html#TAP_TYPE_TOUCH_CANCEL"</a>
{@code TAP_TYPE_TOUCH_CANCEL}</a> event, they cannot trigger a
<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.html#TAP_TYPE_TAP"</a>
{@code TAP_TYPE_TAP}</a> event until they
make a new contact with the screen.</p>

<p>The following example shows you how to implement tap events on a watch face:</p>


<pre>
&#64;Override
public void onTapCommand(
       &#64;TapType int tapType, int x, int y, long eventTime) {
    switch (tapType) {
        case WatchFaceService.TAP_TYPE_TAP:
            hideTapHighlight();
            if (withinTapRegion(x, y)) {
                // Implement the tap action
                // (e.g. show detailed step count)
                onWatchFaceTap();
            }
            break;

        case WatchFaceService.TAP_TYPE_TOUCH:
            if (withinTapRegion(x, y)) {
                // Provide visual feedback of touch event
                startTapHighlight(x, y, eventTime);
            }
            break;

        case WatchFaceService.TAP_TYPE_TOUCH_CANCEL:
            hideTapHighlight();
            break;

        default:
            super.onTapCommand(tapType, x, y, eventTime);
            break;
    }
}
</pre>

<p>In this example, the app determines what kind of event has taken place,
and responds accordingly. If the event is initial contact by the user's finger,
the app displays visual feedback. If the event is an immediate lifting
of the finger after contact, it performs the action on which the
user tapped. If the event is prolonged contact by the finger, the app
does nothing.</p>