android_frameworks_base/docs/html/training/wearables/data-layer/assets.jd

page.title=Transferring Assets

@jd:body

<div id="tb-wrapper">
<div id="tb">

<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#TransferAsset">Transfer an Asset</a></li>
  <li><a href="#ReceiveAsset">Receive an Asset</a></li>
</ol>

</div>
</div>

<p>
To send large blobs of binary data over the Bluetooth transport, such as images, attach an
<a href="{@docRoot}reference/com/google/android/gms/wearable/Asset.html"><code>Asset</code></a> to a
data item and the put the data item into the replicated data store.
</p>

<p>Assets automatically handle caching of data to prevent retransmission and conserve Bluetooth bandwidth.
A common pattern is for a handheld app to download an image, shrink it to an appropriate size
for display on the wearable, and transmit it to the wearable app as an asset. The following examples
demonstrate this pattern.
</p>

<p class="note"><b>Note:</b> Although the size of data items is limited to 100KB,
assets can be as large as desired. However, transferring large assets affects the
user experience in many cases, so test your apps to ensure that they perform well
if you're transferring large assets.
<p>

<h2 id="TransferAsset">Transfer an Asset</h2>
<p>Create the asset using one of the <code>create...()</code> methods in the
<a href="{@docRoot}reference/com/google/android/gms/wearable/Asset.html"><code>Asset</code></a> class.
Here, we convert a bitmap to a byte stream and then call
<a href="{@docRoot}reference/com/google/android/gms/wearable/Asset.html#createFromBytes(byte[])"><code>createFromBytes()</code></a>
to create the asset.
</p>

<pre>
private static Asset createAssetFromBitmap(Bitmap bitmap) {
    final ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
    bitmap.compress(Bitmap.CompressFormat.PNG, 100, byteStream);
    return Asset.createFromBytes(byteStream.toByteArray());
}
</pre>

<p>When you have an asset, attach it to a data item with the <code>putAsset()</code> method in
<a href="{@docRoot}reference/com/google/android/gms/wearable/DataMap.html"><code>DataMap</code></a>
or
<a href="{@docRoot}reference/com/google/android/gms/wearable/PutDataRequest.html"><code>PutDataRequest</code></a>
and then put the data item into the data store with
<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>putDataItem()</code></a>:
</p>

<p><b>Using PutDataRequest</b></p>
<pre>
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);
Asset asset = createAssetFromBitmap(bitmap);
PutDataRequest request = PutDataRequest.create("/image");
request.putAsset("profileImage", asset);
Wearable.DataApi.putDataItem(mGoogleApiClient, request);
</pre>

<p><b>Using PutDataMapRequest</b></p>
<pre>
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);
Asset asset = createAssetFromBitmap(bitmap);
PutDataMapRequest dataMap = PutDataMapRequest.create("/image");
dataMap.getDataMap().putAsset("profileImage", asset)
PutDataRequest request = dataMap.asPutDataRequest();
PendingResult&lt;DataApi.DataItemResult&gt; pendingResult = Wearable.DataApi
        .putDataItem(mGoogleApiClient, request);
</pre>


<h2 id="ReceiveAsset">Receive assets</h2>

<p>
When an asset is created, you probably want to read and extract
it on other side of the connection. Here's an example of how to implement the
callback to detect an asset change and extract the asset:
</p>

<pre>
&#64;Override
public void onDataChanged(DataEventBuffer dataEvents) {
  for (DataEvent event : dataEvents) {
    if (event.getType() == DataEvent.TYPE_CHANGED &&
        event.getDataItem().getUri().getPath().equals("/image")) {
      DataMapItem dataMapItem = DataMapItem.fromDataItem(event.getDataItem());
      Asset profileAsset = dataMapItem.getDataMap().getAsset("profileImage");
      Bitmap bitmap = loadBitmapFromAsset(profileAsset);
      // Do something with the bitmap
    }
  }
}

public Bitmap loadBitmapFromAsset(Asset asset) {
    if (asset == null) {
        throw new IllegalArgumentException("Asset must be non-null");
    }
    ConnectionResult result =
           mGoogleApiClient.blockingConnect(TIMEOUT_MS, TimeUnit.MILLISECONDS);
    if (!result.isSuccess()) {
        return null;
    }
    // convert asset into a file descriptor and block until it's ready
    InputStream assetInputStream = Wearable.DataApi.getFdForAsset(
            mGoogleApiClient, asset).await().getInputStream();
            mGoogleApiClient.disconnect();

    if (assetInputStream == null) {
        Log.w(TAG, "Requested an unknown Asset.");
        return null;
    }
    // decode the stream into a bitmap
    return BitmapFactory.decodeStream(assetInputStream);
}
</pre>