發送與接收消息 · Android Training官方培訓課程中文版

> 編寫:[wly2014](https://github.com/wly2014) - 原文: [http://developer.android.com/training/wearables/data-layer/messages.html](http://developer.android.com/training/wearables/data-layer/messages.html) 使用[MessageApi](#)發送消息，要附加以下幾項： - 任一payload(可選); - 唯一確定的message's action 的 path。不像數據元，Messages(消息)在手持和可穿戴應用之間沒有同步。Messages是單向交流機制，這有利于遠程進程調用(RPC)，比如：發送消息到可穿戴設備以開啟[activity](# "An activity represents a single screen with a user interface.")。 ### 發送消息下面的例子展示如何發送消息到另一連接端開啟一個[activity](# "An activity represents a single screen with a user interface.")。調用是同步的，當收到消息或請求超時時發生阻塞。 > **Note:** 閱讀 [Communicate with Google Play Services](http://developer.android.com/google/auth/api-client.html#Communicating) 了解更多關于異步和同步調用，以及何時使用哪個。 ~~~ GoogleApiClient mGoogleApiClient; public static final String START_ACTIVITY_PATH = "/start/MainActivity"; ... private void sendStartActivityMessage(String nodeId) { Wearable.MessageApi.sendMessage( mGoogleApiClient, nodeId, START_ACTIVITY_PATH, new byte[0]).setResultCallback( new ResultCallback<SendMessageResult>() { @Override public void onResult(SendMessageResult sendMessageResult) { if (!sendMessageResult.getStatus().isSuccess()) { Log.e(TAG, "Failed to send message with status code: " + sendMessageResult.getStatus().getStatusCode()); } } } ); } ~~~ 這是一個簡單的方法，來獲得一列你可能發送消息給它們的連接點： ~~~ 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; } ~~~ ### 接收消息為了在收到消息時被提醒，你可以實現 [MessageListener](http://developer.android.com/reference/com/google/android/gms/wearable/MessageApi.MessageListener.html)接口來提供消息事件的監聽，你需要在 [MessageApi.addListener()](http://developer.android.com/reference/com/google/android/gms/wearable/MessageApi.html#addListener(com.google.android.gms.common.api.GoogleApiClient, com.google.android.gms.wearable.MessageApi.MessageListener))方法中注冊監聽。這個例子展示你可以通過檢查上例中發送消息時使用到的START_ACTIVITY_PATH的狀態，若是true,特定的[activity](# "An activity represents a single screen with a user interface.")就會啟動。 ~~~ @Override public 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); } } ~~~ 這僅是實現更多細節的一小段，如何在service 或 [activity](# "An activity represents a single screen with a user interface.") 實現完整的監聽，請參見 [Listening for Data Layer Events](http://developer.android.com/training/wearables/data-layer/events.html#Listen) 。