Mar 4, 2015
Oct 1, 2015 (Retired)
Denley Bihari (denley)
Denley Bihari (denley)
Source code
APK file



A delivery service for Android Wear. Courier uses Wearable.DataApi and Wearable.MessageApi to deliver objects between devices simply and cleanly.


Build Dependency

Using the jcenter repository, add the following line to the gradle dependencies for your modules. You should add this to both your handheld and wearable modules.

compile 'me.denley.courier:courier:1.2.1'

Basic Usage

Simply add @ReceiveMessages and @ReceiveData annotations to your methods and fields to assign them as callbacks for MessageApi and DataApi events. Call Courier.startReceiving(this) to initialize the listeners and start receiving your callbacks.

public class MainActivity extends Activity  {

    String loggedInUser;

    @Override protected void onCreate(Bundle savedInstanceState) {


    @Override protected void onDestroy() {

    void onSmsReceived(SmsDescriptor smsMessage, String nodeId) { // The nodeId parameter is optional
        // ...


On the other device, use `Courier.deliverMessage` and `Courier.deliverData` to easily send data using the `MessageApi` and `DataApi`, respectively
public void onLoginSuccess(String username) {
    Courier.deliverData(this, "/username", username);

Checking for Connected Devices

Wearable API Status

Often it will be prudent to check whether or not the user has a wearable device paired with their phone. For this, you can use the following method:

// This must be done on a background thread
boolean hasWearableDevice = Courier.isWearableApiAvailable(context);

Note: This is not the same as whether or not the watch is in range of the phone ("connected"). It determines whether the user has the Android Wear app installed and has paired a wearable device.

If this method returns false, all other method calls to the Courier class will simply be ignored, and return null where applicable.

Connected Devices

You can retrieve a list of connected devices using the @RemoteNodes annotation. When devices are connected or disconnected, the callback will be invoked again. This represents devices that are paired, in range, and ready to send and receive data and messages.

void onConnectionStateChanged(List<Node> connectedNodes) {
    // Do something with the nodes
    // ...

Local Device

Sometimes having the local node can be useful. For example, you might want to ignore data items originating from the same device.

You can retrieve the local node using the @LocalNode annotation. This will only be updated once, as it never changes. Alternatively, you can retrieve the local node by calling Courier.getLocalNode(context). This must be done on a background thread.

Node localNode;


// This must be done on a background thread
localNode = Courier.getLocalNode(context);


By default, method calls will be made on the main thread. If you want a callback to be made on a background thread, you can use the @BackgroundThread annotation on a method, like so:

void onSmsReceived(SmsDescriptor smsMessage) {
    // ...

Object Serialization

To be delivered between devices, objects must be able to be serialized into a byte array. Objects of any class implementing Serializable can be delivered. This includes primatives, Strings, and many other classes in the Android API. For custom classes it is recommended to avoid relying on the Serializable interface, as it will restrict your ability to change your data structures in the future.

Instead, annotate your classes with Courier's @Deliverable annotation. This will automatically generate methods to convert your objects into a DataMap and back again. For example:

public class SmsDescriptor {

    String sender;
    String messageText;
    long timestamp;


@Deliverable classes support any field types that can be saved into a DataMap as well as any other @Deliverable or Seriializable object types.

Assets can also be included as fields, and should be used for any large blobs of data (anything larger than a few kilobytes). When received, Assets can be opened using the Courier.getAssetInputStream method. @Deliverable classes can also contain Bitmap fields, which will automatically be transferred as Assets.


Often you will want to listen for message and data events outside of your 'Activity' using a WearableListenerService.

Courier is completely compatible with WearableListenerService. In this class your code will look very similar with or without using Courier, but Courier can help you to unpack any messages/data that were sent using Courier.deliverMessage or Courier.deliverData.


@Override public void onMessageReceived(MessageEvent messageEvent) {
    if (messageEvent.getPath().equals("/incoming_sms")) {
        SmsDescriptor mySms = Packager.unpack(this, messageEvent.getData(), SmsDescriptor.class);

        // Do something with the message
        // ...

@Override public void onDataChanged(DataEventBuffer dataEvents) {
    for(DataEvent event:dataEvents) {
        if (event.getUri().getPath().equals("/username")) {
            String username = Packager.unpack(this, event.getDataItem(), String.class);

            // Do something with the data
            // ...

The Courier.getLocalNode convenience method can also be useful in a WearableListenerService, as you might want to ignore data events that are sent from the local device.


  • @DeliverData callbacks will be invoked immediately after calling Courier.startReceiving (but asynchronously).
  • @DeliverData callbacks will also be called immediately when the device connects to a device.
  • @DeliverMessage callbacks will only be invoked at the time that a message is received from the MessageApi (they are missed if the device is disconnected).
  • If an empty message is sent or if a data item is removed, a null object will be passed to the listener. Be sure to check for null values!


Courier supports using mock implementations of the wearable API for unit testing. Simply call Courier.attachMockDataApi, Courier.attachMockMessageApi, and Courier.attachMockNodeApi to provide your testing API implementations. Mocked APIs will be called with a null GoogleApiClient object. Your mock APIs should be attached before making any calls to Courier.startReceiving and you should not attach new APIs until all targets have called Courier.stopReceiving.

ProGuard Configuration

If you use ProGuard, you will need to add the following lines to your configuration. You will probably need to add this to the configurations for both your handheld and wearable modules.

-keep class me.denley.courier.** { *; }
-dontwarn me.denley.courier.compiler.**
-keep class **$$Delivery { *; }
-keep class **DataMapPackager { *; }
-keepclasseswithmembernames class * {
    @me.denley.courier.* <fields>;
-keepclasseswithmembernames class * {
    @me.denley.courier.* <methods>;
-keep @me.denley.courier.* public class * { *; }


Copyright 2015 Denley Bihari

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.