本节由介绍3种数据的发送接收:
1.Data Items : 比特类型数据,限制100KB以内
2.Assets : 资源类型数据,大小无上限
3.Message : 发送消息,触发指令
/training/wearables/data-layer/data-items.html
1.Syncing Data Items
DataItem定义了同步手机和手表的数据接口.一个DataItem对象一般包括下面2个部分:
负载 : 一个比特类型数组,支持任意实现了序列化接口的对象.负载最大是100KB.路径 : 一个唯一的字符串，且必须以＂/"斜杠作为开头,如"/path/to/data"
一般来说是不需要自己实现DataItem接口的,而是通过以下方式:
创建一个PutDataRequest对象,用一个唯一的字符串ID来定义.调用setData()方法将负载数据传入调用DataApi.putDataItem()请求系统来构建数据单元当请求数据单元时,系统会返回实现了DataItem接口的对象
以上的方式并非最佳的选择,还可以通过DataMap的方式来实现,这类似于Bundle.
Sync Data with a Data Map
因为DataMap的方式是用Bundle实现的,所以它帮我们解决了序列化问题,并且可以使用键值对的方式来操控数据.
使用方法
构造一个PutDataMapRequest对象,设置唯一ID.调用PutDataMapRequest.getDataMap()来获取一个数据map.用put...()方法来设置所需的数据.调用PutDataMapRequest.asPutDataRequest()来获取一个PutDataRequest对象.调用DataApi.putDataItem()请求系统传递数据.注意:此时手表和手机若未连接,则会缓存在发送端,待到两端连接时再进行同步.
代码样例
private void syncData() {PutDataMapRequest dataMap = PutDataMapRequest.create("/count");dataMap.getDataMap().putInt(COUNT_KEY, count++);PutDataRequest request = dataMap.asPutDataRequest();PendingResult<DataApi.DataItemResult> pendingResult = Wearable.DataApi.putDataItem(mGoogleApiClient, request);}
Listen for Data Item Events
当任意一端的数据发生变化时,这时候如果想通知到另外一端,可以通过监听数据改变接口来实现:
代码样例
@Overridepublic void onDataChanged(DataEventBuffer dataEvents) {for (DataEvent event : dataEvents) {if (event.getType() == DataEvent.TYPE_DELETED) {Log.d(TAG, "DataItem deleted: " + event.getDataItem().getUri());} else if (event.getType() == DataEvent.TYPE_CHANGED) {Log.d(TAG, "DataItem changed: " + event.getDataItem().getUri());}}}
/training/wearables/data-layer/assets.html
2.Transferring Assets
若想通过蓝牙发送较大的二进制数据块,例如图片,则需要将数据绑定到Asset对象上.
Assets自动地处理了数据缓存的阻止重发和保存蓝牙数据带宽.一个通用模式来处理手机应用下载图片,再处理成适当的尺寸,最后转换成asset发送到手表.
注意:数据单元Data Item被限制在100KB以内,而Assets则是没有限制的.但是传输大数据量的Assets会影响到用户体验,所以若是迫不得已必须传较大的Assets,要多测试.
Transfer an Asset
构建好了Assets,则可以通过PutDataRequest或PutDataMapRequest的方式传递数据
PutDataRequest:
private void transferAsset{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); }
PutDataMapRequest:
private void transferAsset{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<DataApi.DataItemResult> pendingResult = Wearable.DataApi.putDataItem(mGoogleApiClient, request);}
Receive assets
@Overridepublic 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 readyInputStream 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 bitmapreturn BitmapFactory.decodeStream(assetInputStream);}
/training/wearables/data-layer/messages.html
3.Sending and Receiving Messages
可以通过MessageApi来发送以下两种数据:
任意类型的数据拥有唯一键值对的消息动作
与DataItem的双向同步不同,message是单向的.Message通过单向的连接发送到另一端,这有利于远程调用(RPC - remote procedure calls).
Send a Message
以下是一个发送消息启动Activity的样例,在发送消息时,会阻塞线程,直到消息送达或者超时.
Node node; // the connected device to send the message toGoogleApiClient mGoogleApiClient;public static final START_ACTIVITY_PATH = "/start/MainActivity";...SendMessageResult result = Wearable.MessageApi.sendMessage(mGoogleApiClient, node, START_ACTIVITY_PATH, null).await();if (!result.getStatus().isSuccess()) {Log.e(TAG, "ERROR: failed to send Message: " + result.getStatus());}
以下是获取所有的和Android Wear应用相连接的节点.
private Collection<String> getNodes() {HashSet <String>results = new HashSet<String>();NodeApi.GetConnectedNodesResult nodes =Wearable.NodeApi.getConnectedNodes(mGoogleApiClient).await();for (Node node : nodes.getNodes()) {results.add(node.getId());}return results;}
Receive a Message
以下是接收消息的例子,与上一个发送消息的例子对应.在处理接收到的消息之前,需要使用MessageApi.addListener()注册监听器.具体在其他章节中有讲述.
@Overridepublic void onMessageReceived(MessageEvent messageEvent) {if (messageEvent.getPath().equals(START_ACTIVITY_PATH)) {Intent startIntent = new Intent(this, MainActivity.class);startIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);startActivity(startIntent);}}
