Enable Push Notifications in a Salesforce Mobile SDK Android App

Add an entry for androidPushNotificationClientId.
1. In res/values/bootconfig.xml (for native apps):
  1<string name="androidPushNotificationClientId">1234567890</string>
2. In assets/www/bootconfig.json (for hybrid apps):
  1"androidPushNotificationClientId": "1234567890"
This example value represents the project number of the Google project that is authorized to send push notifications to Android devices.
Behind the scenes, Mobile SDK automatically reads this value and uses it to register the device against the Salesforce connected app. Each time the user re-opens the app, Mobile SDK automatically renews the registration. This validation allows Salesforce to send notifications to the connected app.
A device becomes unregistered if:
The app goes unused for an extended period of time
OR
The user logs out of the app
Note
Create a class in your app that implements PushNotificationInterface. PushNotificationInterface is a Mobile SDK Android interface for handling push notifications. PushNotificationInterface has a single method, onPushMessageReceived(Bundle message).
1public interface PushNotificationInterface { 2 public void onPushMessageReceived(Bundle message); 3}
In this method you implement your custom functionality for displaying, or otherwise disposing of, push notifications.

In the onCreate() method of your Application subclass, call the SalesforceSDKManager.setPushNotificationReceiver() method, passing in your implementation of PushNotificationInterface. Call this method immediately after the SalesforceSDKManager.initNative() call.

1@Override
2public void onCreate() {
3    super.onCreate();
4    SalesforceSDKManager.initNative(getApplicationContext(), 
5        new KeyImpl(), MainActivity.class);
6    SalesforceSDKManager.getInstance().
7        setPushNotificationReceiver(myPushNotificationInterface);
8	}

Salesforce Mobile Push Notifications Implementation Guide

Enable Push Notifications in a Salesforce Mobile SDK Android App