The Wearable Data Layer API, which is part of Google Play services, provides a communication channel for your handheld and wearable apps. The API consists of a set of data objects that the system can send and synchronize over the wire and listeners that notify your apps of important events with the data layer:
DataItemprovides data storage with automatic syncing between the handheld and wearable.
MessageApiclass can send messages and is good for remote procedure calls (RPC), such as controlling a handheld's media player from the wearable or starting an intent on the wearable from the handheld. Messages are also great for one-way requests or for a request/response communication model. If the handheld and wearable are connected, the system queues the message for delivery and returns a successful result code. If the devices are not connected, an error is returned. A successful result code does not indicate that the message was delivered successfully as the devices may disconnect after receiving the result code.
Assetobjects are for sending binary blobs of data, such as images. You attach assets to data items and the system automatically takes care of the transfer for you, conserving Bluetooth bandwidth by caching large assets to avoid re-transmission.
lets you listen for important data layer events in a service. The system manages the lifecycle of
binding to the service when it needs to send data items or messages and unbinding the service when no work is needed.
DataListenerin an activity lets you listen for important data layer events when an activity is in the foreground. Using this instead of the
WearableListenerServicelets you listen for changes only when the user is actively using your app.
ChannelApiclass to transfer large data items, such as music and movie files, from a handheld to a wearable device. The Channel API for data transfer has the following benefits:
Assetobjects attached to
DataItemobjects. The Channel API saves disk space unlike the
DataApiclass, which creates a copy of the assets on the local device before synchronizing with connected devices.
Warning: Because these APIs are designed for communication between handhelds and wearables, these are the only APIs you should use to set up communication between these devices. For instance, don't try to open low-level sockets to create a communication channel.
Android Wear supports multiple wearables connected to a handheld device. For example, when the user saves a note on a handheld, it automatically appears on both of the user's Wear devices. To synchronize data between devices, Google’s servers host a cloud node in the network of devices. The system synchronizes data to directly connected devices, the cloud node, and to wearable devices connected to the cloud node via Wi-Fi.