1 page.title=Syncing Data Items 2 3 @jd:body 4 5 <div id="tb-wrapper"> 6 <div id="tb"> 7 8 <h2>This lesson teaches you to</h2> 9 <ol> 10 <li><a href="#SyncData">Sync Data with a Data Map</a></li> 11 <li><a href="#ListenEvents">Listen for Data Item Events</a></li> 12 </ol> 13 14 </div> 15 </div> 16 17 <p> 18 A <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a> 19 defines the data interface that the system uses to synchronize data between handhelds 20 and wearables. A <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a> generally 21 consists of the following items:</p> 22 <ul> 23 <li><b>Payload</b> - A byte array, which you can set with whatever data you wish, allowing you 24 to do your own object serialization and deserialization. The size of the payload is limited 25 to 100KB.</li> 26 <li><b>Path</b> - A unique string that must start with a forward slash (for instance, 27 <code>"/path/to/data"</code>)</li> 28 </ul> 29 30 <p> 31 You normally don't implement <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a> 32 directly. Instead, you: 33 34 <ol> 35 <li>Create a <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html"><code>PutDataRequest</code></a> object, 36 specifying a string path to uniquely identify the item. 37 </li> 38 <li>Call <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html#setData(byte[])"> 39 <code>setData()</code></a> to set the payload. 40 </li> 41 <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. 42 </li> 43 <li>When requesting data items, the system returns objects 44 that properly implement the <a href="{@docRoot}reference/com/google/android/gms/wearable/DataItem.html"><code>DataItem</code></a> interface. 45 </li> 46 </ol> 47 48 <p> 49 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>, 50 we recommend you <a href="#SyncData">use a data map</a>, which exposes 51 a data item in an easy-to-use {@link android.os.Bundle}-like interface. 52 </p> 53 54 55 <h2 id="SyncData">Sync Data with a Data Map</h2> 56 <p> 57 When possible, use the <a href="{@docRoot}reference/com/google/android/gms/wearable/DataMap.html"><code>DataMap</code></a> class. 58 This approach lets you work with data items in the form of an Android {@link android.os.Bundle}, 59 so object serialization and de-serialization is done for you, and you can manipulate data with key-value pairs. 60 </p> 61 62 <p>To use a data map:</p> 63 64 <ol> 65 <li>Create a 66 <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataMapRequest.html"><code>PutDataMapRequest</code></a> 67 object, setting the path of the data item. 68 <p class="note"><b>Note:</b> The path string is a unique identifier for the 69 data item that allows you to access it from either side of the connection. The path must begin 70 with a forward slash. If you're using hierarchical data in your 71 app, you should create a path scheme that matches the structure of the data. 72 </p> 73 </li> 74 <li>Call 75 <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataMapRequest.html#getDataMap()"><code>PutDataMapRequest.getDataMap()</code></a> 76 </a> to obtain a data map that you can set values on.</li> 77 <li>Set any desired values for the data map using the <code>put...()</code> methods, such as 78 <a href="{@docRoot}reference/com/google/android/gms/wearable/DataMap.html#putString(java.lang.String, java.lang.String)"><code>putString()</code></a>. 79 </li> 80 <li>Call <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataMapRequest.html#asPutDataRequest()"><code>PutDataMapRequest.asPutDataRequest()</code></a> 81 to obtain a <a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html"><code>PutDataRequest</code></a> object. 82 </li> 83 <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. 84 <p class="note"><b>Note:</b> 85 If the handset and wearable devices are disconnected, 86 the data is buffered and synced when the connection is re-established. 87 </p> 88 </li> 89 </ol> 90 91 <p>The <code>increaseCounter()</code> method in the following example shows how to create a 92 data map and put data in it:</p> 93 94 <pre> 95 public class MainActivity extends Activity implements 96 DataApi.DataListener, 97 GoogleApiClient.ConnectionCallbacks, 98 GoogleApiClient.OnConnectionFailedListener { 99 100 private static final String COUNT_KEY = "com.example.key.count"; 101 102 private GoogleApiClient mGoogleApiClient; 103 private int count = 0; 104 105 ... 106 107 // Create a data map and put data in it 108 private void <strong>increaseCounter</strong>() { 109 PutDataMapRequest putDataMapReq = PutDataMapRequest.create("/count"); 110 putDataMapReq.getDataMap().putInt(COUNT_KEY, count++); 111 PutDataRequest putDataReq = putDataMapReq.asPutDataRequest(); 112 PendingResult<DataApi.DataItemResult> pendingResult = 113 Wearable.DataApi.putDataItem(mGoogleApiClient, putDataReq); 114 } 115 116 ... 117 } 118 </pre> 119 120 <p>For more information about handling the 121 <a href="{@docRoot}reference/com/google/android/gms/common/api/PendingResult.html"> 122 <code>PendingResult</code></a> object, see 123 <a href="{@docRoot}training/wearables/data-layer/events.html#Wait">Wait for the Status of Data 124 Layer Calls</a>.</p> 125 126 127 <h2 id="ListenEvents">Listen for Data Item Events</h2> 128 129 <p>If one side of the data layer connection changes a data item, you probably want 130 to be notified of any changes on the other side of the connection. 131 You can do this by implementing a listener for data item events.</p> 132 133 <p>The code snippet in the following example notifies your app when the value of the 134 counter defined in the previous example changes:</p> 135 136 <pre> 137 public class MainActivity extends Activity implements 138 DataApi.DataListener, 139 GoogleApiClient.ConnectionCallbacks, 140 GoogleApiClient.OnConnectionFailedListener { 141 142 private static final String COUNT_KEY = "com.example.key.count"; 143 144 private GoogleApiClient mGoogleApiClient; 145 private int count = 0; 146 147 @Override 148 protected void onCreate(Bundle savedInstanceState) { 149 super.onCreate(savedInstanceState); 150 setContentView(R.layout.activity_main); 151 152 mGoogleApiClient = new GoogleApiClient.Builder(this) 153 .addApi(Wearable.API) 154 .addConnectionCallbacks(this) 155 .addOnConnectionFailedListener(this) 156 .build(); 157 } 158 159 @Override 160 protected void onResume() { 161 super.onStart(); 162 mGoogleApiClient.connect(); 163 } 164 165 @Override 166 public void onConnected(Bundle bundle) { 167 <strong>Wearable.DataApi.addListener</strong>(mGoogleApiClient, this); 168 } 169 170 @Override 171 protected void onPause() { 172 super.onPause(); 173 <strong>Wearable.DataApi.removeListener</strong>(mGoogleApiClient, this); 174 mGoogleApiClient.disconnect(); 175 } 176 177 @Override 178 public void <strong>onDataChanged</strong>(DataEventBuffer dataEvents) { 179 for (DataEvent event : dataEvents) { 180 if (event.getType() == DataEvent.TYPE_CHANGED) { 181 // DataItem changed 182 DataItem item = event.getDataItem(); 183 if (item.getUri().getPath().compareTo("/count") == 0) { 184 DataMap dataMap = DataMapItem.fromDataItem(item).getDataMap(); 185 updateCount(dataMap.getInt(COUNT_KEY)); 186 } 187 } else if (event.getType() == DataEvent.TYPE_DELETED) { 188 // DataItem deleted 189 } 190 } 191 } 192 193 // Our method to update the count 194 private void updateCount(int c) { ... } 195 196 ... 197 } 198 </pre> 199 200 <p>This activity implements the 201 <a href="{@docRoot}reference/com/google/android/gms/wearable/DataApi.DataListener.html"> 202 <code>DataItem.DataListener</code></a> interface. This activity adds itself as a listener 203 for data item events inside the <code>onConnected()</code> method and removes the listener 204 in the <code>onPause()</code> method.</p> 205 206 <p>You can also implement the listener as a service. For more information, see 207 <a href="{@docRoot}training/wearables/data-layer/events.html#Listen">Listen for Data Layer 208 Events</a>.</p> 209
