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page.title=Syncing Data Items
@jd:body
<div id="tb-wrapper">
<div id="tb">
<h2>This lesson teaches you to</h2>
<ol>
<li><a href="#SyncData">Sync Data with a Data Map</a></li>
<li><a href="#ListenEvents">Listen for Data Item Events</a></li>
</ol>
</div>
</div>
<p>
A <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a>
defines the data interface that the system uses to synchronize data between handhelds
and wearables. A <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a> generally
consists of the following items:</p>
<ul>
<li><b>Payload</b> - A byte array, which you can set with whatever data you wish, allowing you
to do your own object serialization and deserialization. The size of the payload is limited
to 100KB.</li>
<li><b>Path</b> - A unique string that must start with a forward slash (for instance,
<code>"/path/to/data"</code>)</li>
</ul>
<p>
You normally don't implement <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a>
directly. Instead, you:
<ol>
<li>Create a <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html"><code>PutDataRequest</code></a> object,
specifying a string path to uniquely identify the item.
</li>
<li>Call <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html#setData(byte[])">
<code>setData()</code></a> to set the payload.
</li>
<li>Call <a href="{@docRoot}reference/com/google/android/gms/wearable/DataApi.html#putDataItem(com.google.android.gms.common.api.GoogleApiClient, com.google.android.gms.wearable.PutDataRequest)"><code>DataApi.putDataItem()</code></a> to request the system to create the data item.
</li>
<li>When requesting data items, the system returns objects
that properly implement the <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a> interface.
</li>
</ol>
<p>
However, instead of working with raw bytes using <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html#setData(byte[])"><code>setData()</code></a>,
we recommend you <a href="#SyncData">use a data map</a>, which exposes
a data item in an easy-to-use {@link android.os.Bundle}-like interface.
</p>
<h2 id="SyncData">Sync Data with a Data Map</h2>
<p>
When possible, use the <a href="{@docRoot}reference/com/google/android/gms/wearable/DataMap.html"><code>DataMap</code></a> class.
This approach lets you work with data items in the form of an Android {@link android.os.Bundle},
so object serialization and de-serialization is done for you, and you can manipulate data with key-value pairs.
</p>
<p>To use a data map:</p>
<ol>
<li>Create a
<a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataMapRequest.html"><code>PutDataMapRequest</code></a>
object, setting the path of the data item.
<p class="note"><b>Note:</b> The path string is a unique identifier for the
data item that allows you to access it from either side of the connection. The path must begin
with a forward slash. If you're using hierarchical data in your
app, you should create a path scheme that matches the structure of the data.
</p>
</li>
<li>Call
<a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataMapRequest.html#getDataMap()"><code>PutDataMapRequest.getDataMap()</code></a>
</a> to obtain a data map that you can set values on.</li>
<li>Set any desired values for the data map using the <code>put...()</code> methods, such as
<a href="{@docRoot}reference/com/google/android/gms/wearable/DataMap.html#putString(java.lang.String, java.lang.String)"><code>putString()</code></a>.
</li>
<li>Call <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataMapRequest.html#asPutDataRequest()"><code>PutDataMapRequest.asPutDataRequest()</code></a>
to obtain a <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html"><code>PutDataRequest</code></a> object.
</li>
<li>Call <a href="{@docRoot}reference/com/google/android/gms/wearable/DataApi.html#putDataItem(com.google.android.gms.common.api.GoogleApiClient, com.google.android.gms.wearable.PutDataRequest)"><code>DataApi.putDataItem()</code></a> to request the system to create the data item.
<p class="note"><b>Note:</b>
If the handset and wearable devices are disconnected,
the data is buffered and synced when the connection is re-established.
</p>
</li>
</ol>
<p>The <code>increaseCounter()</code> method in the following example shows how to create a
data map and put data in it:</p>
<pre>
public class MainActivity extends Activity implements
DataApi.DataListener,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener {
private static final String COUNT_KEY = "com.example.key.count";
private GoogleApiClient mGoogleApiClient;
private int count = 0;
...
// Create a data map and put data in it
private void <strong>increaseCounter</strong>() {
PutDataMapRequest putDataMapReq = PutDataMapRequest.create("/count");
putDataMapReq.getDataMap().putInt(COUNT_KEY, count++);
PutDataRequest putDataReq = putDataMapReq.asPutDataRequest();
PendingResult<DataApi.DataItemResult> pendingResult =
Wearable.DataApi.putDataItem(mGoogleApiClient, putDataReq);
}
...
}
</pre>
<p>For more information about handling the
<a href="{@docRoot}reference/com/google/android/gms/common/api/PendingResult.html">
<code>PendingResult</code></a> object, see
<a href="{@docRoot}training/wearables/data-layer/events.html#Wait">Wait for the Status of Data
Layer Calls</a>.</p>
<h2 id="ListenEvents">Listen for Data Item Events</h2>
<p>If one side of the data layer connection changes a data item, you probably want
to be notified of any changes on the other side of the connection.
You can do this by implementing a listener for data item events.</p>
<p>The code snippet in the following example notifies your app when the value of the
counter defined in the previous example changes:</p>
<pre>
public class MainActivity extends Activity implements
DataApi.DataListener,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener {
private static final String COUNT_KEY = "com.example.key.count";
private GoogleApiClient mGoogleApiClient;
private int count = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addApi(Wearable.API)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.build();
}
@Override
protected void onResume() {
super.onStart();
mGoogleApiClient.connect();
}
@Override
public void onConnected(Bundle bundle) {
<strong>Wearable.DataApi.addListener</strong>(mGoogleApiClient, this);
}
@Override
protected void onPause() {
super.onPause();
<strong>Wearable.DataApi.removeListener</strong>(mGoogleApiClient, this);
mGoogleApiClient.disconnect();
}
@Override
public void <strong>onDataChanged</strong>(DataEventBuffer dataEvents) {
for (DataEvent event : dataEvents) {
if (event.getType() == DataEvent.TYPE_CHANGED) {
// DataItem changed
DataItem item = event.getDataItem();
if (item.getUri().getPath().compareTo("/count") == 0) {
DataMap dataMap = DataMapItem.fromDataItem(item).getDataMap();
updateCount(dataMap.getInt(COUNT_KEY));
}
} else if (event.getType() == DataEvent.TYPE_DELETED) {
// DataItem deleted
}
}
}
// Our method to update the count
private void updateCount(int c) { ... }
...
}
</pre>
<p>This activity implements the
<a href="{@docRoot}reference/com/google/android/gms/wearable/DataApi.DataListener.html">
<code>DataItem.DataListener</code></a> interface. This activity adds itself as a listener
for data item events inside the <code>onConnected()</code> method and removes the listener
in the <code>onPause()</code> method.</p>
<p>You can also implement the listener as a service. For more information, see
<a href="{@docRoot}training/wearables/data-layer/events.html#Listen">Listen for Data Layer
Events</a>.</p>
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