| 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> |
| If a delay in syncing would negatively impact user experience, call |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest#setUrgent()"> |
| {@code setUrgent()}</a>. |
| </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> |
| </ol> |
| |
| <p> |
| 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. 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 the system does object serialization and deserialization 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> |
| If a delay in syncing would negatively impact user experience, call |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest#setUrgent()"> |
| {@code setUrgent()}</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> |
| |
| |
| <h3>Set DataItem priority</h3> |
| |
| <p> |
| In <a href="https://developers.google.com/android/guides/releases">Google Play services 8.3 and later</a>, |
| the |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/DataApi">{@code DataApi}</a> interface |
| allows urgent requests for syncing of |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem">{@code DataItems}</a>. |
| Normally, the system may delay delivery of |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem">{@code DataItems}</a> |
| to the Wear network in order to improve battery life |
| for user devices, but if a delay in syncing |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem">{@code DataItems}</a> |
| would negatively impact user experience, you |
| can mark them as urgent. For example, in a remote control app where the user expects their actions to be |
| reflected immediately, you can have the system sync your |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem">{@code DataItems}</a> |
| immediately by calling |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest#setUrgent()"> |
| {@code setUrgent()}</a>. |
| </p> |
| |
| <p> |
| If you do not call |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest#setUrgent()"> |
| {@code setUrgent()}</a>, the system may delay up to 30 minutes before syncing non-urgent |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem">{@code DataItems}</a>, |
| but you can usually expect the delay to be a few minutes, if at all. |
| The default urgency is now non-urgent, so you must use |
| <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest#setUrgent()"> |
| {@code setUrgent()}</a> if you wish to retain the immediate-sync behavior that |
| existed in previous versions of the Wear API. |
| </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.onResume(); |
| 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> |