Android Wear开发 - 数据通讯 - 事件处理

http://developer.android.com/training/wearables/data-layer/events.html#Wait

Section 1 :

Wait for the Status of Data Layer Calls- 等待数据操作结果

You‘ll notice that calls to the data layer API sometimes return a PendingResult, such as putDataItem(). As soon as the PendingResult is created, the operation is queued in the background. If you do nothing else after this, the operation eventually completes silently. However, you‘ll usually want to do something with the result after the operation completes, so the PendingResult lets you wait for the result status, either synchronously or asynchronously.

在进行数据通讯的时候,有时候会返回一个PendingResult对象,例如调用了putDataItem方法.一旦PendingResult对象被构建了,那么数据操作就会在后台队列中.你可以选择是否对这个操作结果进行处理.PendingResult对象可以让你获取到操作结果,无论是同步还是异步.

Asynchronously waiting-异步等待

If your code is running on the main UI thread, do not making blocking calls to the data layer API. You can run the calls asynchronously by adding a callback to the PendingResult object, which fires when the operation is completed:

若你是在UI线程中执行数据操作,那么小心阻塞问题.在这里可以使用回调监听的方式来实现异步等待:

pendingResult.setResultCallback(new ResultCallback<DataItemResult>() {
    @Override
    public void onResult(final DataItemResult result) {
        if(result.getStatus().isSuccess()) {
            Log.d(TAG, "Data item set: " + result.getDataItem().getUri());
        }
    }
});

Synchronously waiting-同步等待

If your code is running on a separate handler thread in a background service (which is the case in a WearableListenerService), it‘s fine for the calls to block. In this case, you can call await() on the PendingResult object, which will block until the request has completed, and return a Result object:

若你在独立的后台服务进程中进行数据操作,那么可以使用同步等待的方式来处理操作结果,在获取到处理结果前都会阻塞住进程.

DataItemResult result = pendingResult.await();
if(result.getStatus().isSuccess()) {
    Log.d(TAG, "Data item set: " + result.getDataItem().getUri());
}

Section 2 :

Listen for Data Layer Events- 监听数据层事件

Because the data layer synchronizes and sends data across the handheld and wearable, you normally want to listen for important events, such as when data items are created, messages are received, or when the wearable and handset are connected.

因为在手机和手表的数据通讯同步的,所以通常需要监听一些重要的事件,如数据创建,消息接收,通讯的连接.

To listen for data layer events, you have two options:

1. Create a service that extends WearableListenerService.
2. Create an activity that implements DataApi.DataListener.

With both these options, you override any of the data event callbacks that you care about handling in your implementation.

监听数据通讯,可以通过以下两种方式实现:

1. 创建一个继承自WearableListenerService的Service
2. 创建一个实现了DataApi.DataListener数据接口的Activity

1.With a WearableListenerService

You typically create instances of this service in both your wearable and handheld apps. If you don‘t care about data events in one of these apps, then you don‘t need to implement this service in that particular app.
For example, you can have a handheld app that sets and gets data item objects and a wearable app that listens for these updates to update it‘s UI. The wearable never updates any of the data items, so the handheld app doesn‘t listen for any data events from the wearable app.

使用情景

一般而言都会在手机端和手表端都构建一个这样的子类Service. 但如果哪一端对数据事件的监听处理没什么需求,那一端则无需构建.

例如,你可以在手机端构建和传递数据给手表,手表则监听这些数据事件来更新自身界面.但手表端只是单方面的获取数据,不会对数据进行做任何修改,那么,手机端则无需监听数据通讯事件.

You can listen for the following events with WearableListenerService:

• onDataChanged() - Called when data item objects are created, changed, or deleted. An event on one side of a connection triggers this callback on both sides.
• onMessageReceived() - A message sent from one side of a connection triggers this callback on the other side of the connection.
• onPeerConnected() and onPeerDisconnected() - Called when connection with the handheld or wearable is connected or disconnected. Changes in connection state on one side of the connection triggers these callbacks on both sides of the connection.

方法介绍

接下来是介绍WearableListenerService的一些重要事件方法:

• onDataChanged() :增,删,改,这三种事件都会调用这个接口.并且是两端都会被触发调用.→双向
• onMessageReceived():消息从一端发送,会调用另一端的接口.→单向
• onPeerConnected() , onPeerDisconnected():当两端进行连接或者断开的时候会触发.改变一端的连接状态都会调用两端的接口.→双向

To create a WearableListenerService:

1. Create a class that extends WearableListenerService.
2. Listen for the events that you care about, such as onDataChanged().
3. Declare an intent filter in your Android manifest to notify the system about your WearableListenerService. This allows the system to bind your service as needed.

实现步骤

1. 继承WearableListenerService
2. 监听数据通讯事件
3. 在Manifest中声明,并添加intent filter监听com.google.android.gms.wearable.BIND_LISTENER这个动作

代码样例

public class DataLayerListenerService extends WearableListenerService {

    private static final String TAG = "DataLayerSample";
    private static final String START_ACTIVITY_PATH = "/start-activity";
    private static final String DATA_ITEM_RECEIVED_PATH = "/data-item-received";

    @Override
    public void onDataChanged(DataEventBuffer dataEvents) {
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "onDataChanged: " + dataEvents);
        }
        final List events = FreezableUtils
                .freezeIterable(dataEvents);

        GoogleApiClient googleApiClient = new GoogleApiClient.Builder(this)
                .addApi(Wearable.API)
                .build();

        ConnectionResult connectionResult =
                googleApiClient.blockingConnect(30, TimeUnit.SECONDS);

        if (!connectionResult.isSuccess()) {
            Log.e(TAG, "Failed to connect to GoogleApiClient.");
            return;
        }

        // Loop through the events and send a message
        // to the node that created the data item.
        for (DataEvent event : events) {
            Uri uri = event.getDataItem().getUri();

            // Get the node id from the host value of the URI
            String nodeId = uri.getHost();
            // Set the data of the message to be the bytes of the URI.
            byte[] payload = uri.toString().getBytes();

            // Send the RPC
            Wearable.MessageApi.sendMessage(googleApiClient, nodeId,
                    DATA_ITEM_RECEIVED_PATH, payload);
        }
    }
}

Manifest声明

<service android:name=".DataLayerListenerService">
  <intent-filter>
      <action android:name="com.google.android.gms.wearable.BIND_LISTENER" />
  </intent-filter>
</service>

Permissions within Data Layer Callbacks

In order to deliver callbacks to your application for data layer events, Google Play services binds to yourWearableListenerService, and calls your callbacks via IPC. This has the consequence that your callbacks inherit the permissions of the calling process.

If you try to perform a privileged operation within a callback, the security check fails because your callback is running with the identity of the calling process, instead of the identity of your app‘s process.

To fix this, call clearCallingIdentity() , to reset identity after crossing the IPC boundary, and then restore identity with restoreCallingIdentity() when you‘ve completed the privileged operation:

注意点

数据回调接口中的权限问题
为了回调数据事件接口,Google Play会绑定你的Service并且通过IPC的方式调用.这也导致了你的回调接口继承了调用进程的权限.
若想要在回调接口中做某些特权操作,你会发现安全验证失败了,你会发现回调接口中打印出来的进程id,是在触发回调接口的进程的id,而不是你的应用的进程.
为了解决这个问题,先调用clearCallingIdentity()来重置id,恢复为应用进程id;再执行你所需要的操作;最后再调用恢复为restoreCallingIdentity()调用者的id.

long token = Binder.clearCallingIdentity();
try {
    performOperationRequiringPermissions();
} finally {
    Binder.restoreCallingIdentity(token);
}

2.With a Listener Activity

If your app only cares about data layer events when the user is interacting with the app and does not need a long-running service to handle every data change, you can listen for events in an activity by implementing one or more of the following interfaces:

• DataApi.DataListener
• MessageApi.MessageListener
• NodeApi.NodeListener

方法介绍

若你的应用只是需要在用户打开时监听数据通讯事件,而不需要在后台监听数据改变,那么可以实现以下接口来实现你的需求.

• DataApi.DataListener
• MessageApi.MessageListener
• NodeApi.NodeListener

To create an activity that listens for data events:

1. Implement the desired interfaces.
2. In onCreate(Bundle), create an instance of GoogleApiClient to work with the data layer API.
3. In onStart(), call connect() to connect the client to Google Play services.
4. When the connection to Google Play services is established, the system calls onConnected(). This is where you call DataApi.addListener(), MessageApi.addListener(), or NodeApi.addListener() to notify Google Play services that your activity is interested in listening for data layer events.
5. In onStop(), unregister any listeners with DataApi.removeListener(), MessageApi.removeListener(), or NodeApi.removeListener().
6. Implement onDataChanged(), onMessageReceived(), onPeerConnected(), and onPeerDisconnected(), depending on the interfaces that you implemented.

实现步骤

接下来是创建一个监听数据通讯事件的Activity

1. 实现接口 : 实现上面列举的接口(根据需求来定,不需要全部都实现)
2. 创建服务对象 : 在onCreate方法中创建一个GoogleApiClient对象来实现与数据通讯的连接.
3. 连接服务 : 在onStart方法中调用GoogleApiClient的connect方法来连接服务
4. 注册监听器 : 当GoogleApiClient连接上了服务,会回调onConnected方法,那么我们就可以在这里中注册监听器,来监听我们所关心的通讯事件.
5. 反注册监听器,并断开服务 : 在onStop方法中,反注册之前注册的监听器,然后再断开GoogleApiClient服务连接.
6. 实现事件回调接口 : 根据注册的监听器实现接口,处理相关的需求.

代码样例

以下是一个实现了DataApi.DataListener的样例:

public class MainActivity extends Activity implements
        DataApi.DataListener, ConnectionCallbacks, OnConnectionFailedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addApi(Wearable.API)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .build();
    }

    @Override
    protected void onStart() {
        super.onStart();
        if (!mResolvingError) {
            mGoogleApiClient.connect();
        }
    }

   @Override
    public void onConnected(Bundle connectionHint) {
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "Connected to Google Api Service");
        }
        Wearable.DataApi.addListener(mGoogleApiClient, this);
    }

    @Override
    protected void onStop() {
        if (null != mGoogleApiClient && mGoogleApiClient.isConnected()) {
            Wearable.DataApi.removeListener(mGoogleApiClient, this);
            mGoogleApiClient.disconnect();
        }
        super.onStop();
    }

    @Override
    public 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());
            }
        }
    }