apply plugin: 'android'
...

dependencies {
    compile 'com.google.android.gms:play-services-nearby:8.4.0'
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.google.sample.app" >
    <application ...>
        <meta-data
            android:name="com.google.android.nearby.messages.API_KEY"
            android:value="API_KEY" />
        <activity>
        ...
        </activity>
    </application>
</manifest>

mGoogleApiClient = new GoogleApiClient.Builder(this)
     .addApi(Nearby.MESSAGES_API)
     .addConnectionCallbacks(this)
     .addOnConnectionFailedListener(this)
     .build();

private void handleUnsuccessfulNearbyResult(Status status) {
    Log.i(TAG, "Processing error, status = " + status);
    if (mResolvingError) {
        // Already attempting to resolve an error.
        return;
    } else if (status.hasResolution()) {
        try {
            mResolvingError = true;
            status.startResolutionForResult(getActivity(),
                    Constants.REQUEST_RESOLVE_ERROR);
        } catch (IntentSender.SendIntentException e) {
            mResolvingError = false;
            Log.i(TAG, "Failed to resolve error status.", e);
        }
    } else {
        if (status.getStatusCode() == CommonStatusCodes.NETWORK_ERROR) {
            Toast.makeText(getActivity().getApplicationContext(),
                    "No connectivity, cannot proceed. Fix in 'Settings' and try again.",
                    Toast.LENGTH_LONG).show();
        } else {
            // To keep things simple, pop a toast for all other error messages.
            Toast.makeText(getActivity().getApplicationContext(), "Unsuccessful: " +
                    status.getStatusMessage(), Toast.LENGTH_LONG).show();
        }
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == Constants.REQUEST_RESOLVE_ERROR) {
        // User was presented with the Nearby opt-in dialog and pressed "Allow".
        mResolvingError = false;
        if (resultCode == Activity.RESULT_OK) {
            // Execute the pending subscription and publication tasks here.
            mMainFragment.executePendingTasks();
        } else if (resultCode == Activity.RESULT_CANCELED) {
            // User declined to opt-in. Reset application state here.
        } else {
            Toast.makeText(this, "Failed to resolve error with code " + resultCode,
                    Toast.LENGTH_LONG).show();
        }
    }

// Create a new message listener.
mMessageListener = new MessageListener() {
    @Override
    public void onFound(Message message) {
        // Do something with the message.
        Log.i(TAG, "Found message: " + message);
    }

    // Called when a message is no longer detectable nearby.
    public void onLost(Message message) {
        // Take appropriate action here (update UI, etc.)
    }
}

// Subscribe to receive messages.
Log.i(TAG, "Trying to subscribe.");
// Connect the GoogleApiClient.
if (!mGoogleApiClient.isConnected()) {
    if (!mGoogleApiClient.isConnecting()) {
        mGoogleApiClient.connect();
    }
} else {
    SubscribeOptions options = new SubscribeOptions.Builder()
            .setStrategy(Strategy.BLE_ONLY)
            .setCallback(new SubscribeCallback() {
                @Override
                public void onExpired() {
                    Log.i(TAG, "No longer subscribing.");
                }
            }).build();

    Nearby.Messages.subscribe(mGoogleApiClient, mMessageListener, options)
            .setResultCallback(new ResultCallback<Status>() {
                @Override
                public void onResult(Status status) {
                    if (status.isSuccess()) {
                        Log.i(TAG, "Subscribed successfully.");
                    } else {
                        Log.i(TAG, "Could not subscribe.");
                        // Check whether consent was given;
                        // if not, prompt the user for consent.
                        handleUnsuccessfulNearbyResult(status);
                    }
                }
            });
}

// Subscribe to messages in the background.
private void backgroundSubscribe() {
    // Connect the GoogleApiClient.
    if (!mGoogleApiClient.isConnected()) {
        if (!mGoogleApiClient.isConnecting()) {
            mGoogleApiClient.connect();
        }
    } else {
        Log.i(TAG, "Subscribing for background updates.");
        SubscribeOptions options = new SubscribeOptions.Builder()
                .setStrategy(Strategy.BLE_ONLY)
                .build();
        Nearby.Messages.subscribe(mGoogleApiClient, getPendingIntent(), options)
                .setResultCallback(new ResultCallback<Status>() {
                    @Override
                    public void onResult(Status status) {
                        if (status.isSuccess()) {
                            Log.i(TAG, "Subscribed successfully.");
                        } else {
                            Log.i(TAG, "Could not subscribe.");
                            handleUnsuccessfulNearbyResult(status);
                        }
                    }
                });
    }
}

private PendingIntent getPendingIntent() {
    return PendingIntent.getService(getApplicationContext(), 0,
            getBackgroundSubscribeServiceIntent(), PendingIntent.FLAG_UPDATE_CURRENT);
}

private Intent getBackgroundSubscribeServiceIntent() {
    return new Intent(getApplicationContext(), BackgroundSubscribeIntentService.class);
}

protected void onHandleIntent(Intent intent) {
    Nearby.Messages.handleIntent(intent, new MessageListener() {
        @Override
        public void onFound(Message message) {
            Log.i(TAG, "Found message via PendingIntent: " + message);
        }

        @Override
        public void onLost(Message message) {
            Log.i(TAG, "Lost message via PendingIntent: " + message);
        }
    });
}

mMessageListener = new MessageListener() {
    @Override
    public void onFound(Message message) {
        // Do something with the message here.
        Log.i(TAG, "Message found: " + message);
        Log.i(TAG, "Message string: " + new String(message.getContent()));
        Log.i(TAG, "Message namespaced type: " + message.getNamespace() +
                "/" + message.getType());
    }

    ...
};

_beaconSubscription = [_messageManager
    subscriptionWithMessageFoundHandler:myMessageFoundHandler
                     messageLostHandler:myMessageLostHandler
                            paramsBlock:^(GNSSubscriptionParams *params) {
                              params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
                            }];

_beaconSubscription = [_messageManager
    subscriptionWithMessageFoundHandler:myMessageFoundHandler
                     messageLostHandler:myMessageLostHandler
                            paramsBlock:^(GNSSubscriptionParams *params) {
                              params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
                              params.messageNamespace = @"com.mycompany.mybeaconservice";
                              params.type = @"mybeacontype";
                            }];

_beaconSubscription = [_messageManager
    subscriptionWithMessageFoundHandler:myMessageFoundHandler
                     messageLostHandler:myMessageLostHandler
                            paramsBlock:^(GNSSubscriptionParams *params) {
                              params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
                              params.messageNamespace = @"com.mycompany.mybeaconservice";
                              params.type = @"mybeacontype";
                              params.beaconStrategy = [GNSBeaconStrategy strategyWithParamsBlock:^(GNSBeaconStrategyParams *params) {
                                params.includeIBeacons = NO;
                              };
                            }];

_beaconSubscription = [_messageManager
    subscriptionWithMessageFoundHandler:myMessageFoundHandler
                     messageLostHandler:myMessageLostHandler
                            paramsBlock:^(GNSSubscriptionParams *params) {
                              params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
                              params.messageNamespace = @"com.mycompany.mybeaconservice";
                              params.type = @"mybeacontype";
                              params.beaconStrategy = [GNSBeaconStrategy strategyWithParamsBlock:^(GNSBeaconStrategyParams *params) {
                                params.includeIBeacons = NO;
                              };
                              params.permissionRequestHandler = ^(GNSPermissionHandler permissionHandler) {
                                // Show your custom dialog here, and don't forget to call permissionHandler after it is dismissed
                                permissionHandler(userGavePermission);
                              };
                            }];