Join us on the livestream at Android Dev Summit on 7-8 November 2018, starting at 10AM PDT!

Detect when users start or end an activity

It might be necessary to design your app to identify when a user starts or stops a particular activity, such as walking, biking, or driving. For example, a mileage tracking app could start tracking miles when a user starts driving, or a messaging app could mute all conversations until the user stops driving.

The Activity Recognition Transition API can be used to detect changes in the user's activity. Your app subscribes to a transition in activities of interest and the API notifies your app only when needed. This page shows how to use the Activity Recognition Transition API, also called the Transition API for short.

Set up your project

To use the Transition API in your app, you must declare a dependency to the Google Location and Activity Recognition API version 12.0.0 or higher and specify the com.google.android.gms.permission.ACTIVITY_RECOGNITION permission in the app manifest.

  1. To declare a dependency to the API, add a reference to the Google maven repository and add an implementation entry to com.google.android.gms:play-services-location:12.0.0 to the dependencies section of your app build.gradle file. For more information, see Set Up Google Play Services.
  2. To specify the com.google.android.gms.permission.ACTIVITY_RECOGNITION permission, add a <uses-permission> element in the app manifest, as shown in the following example:

     <manifest xmlns:android="http://schemas.android.com/apk/res/android"
             package="com.example.myapp">
    
       <uses-permission android:name="com.google.android.gms.permission.ACTIVITY_RECOGNITION" />
       …
     </manifest>
    

Register for activity transition updates

To start receiving notifications about activity transitions, you must implement the following:

To create the ActivityTransitionRequest object, you must create a list of ActivityTransition objects, which represent the transition that you want to receive notifications about. An ActivityTransition object includes the following data:

The following code shows how to create a list of ActivityTransition objects:

List<ActivityTransition> transitions = new ArrayList<>();

transitions.add(
  new ActivityTransition.Builder()
    .setActivityType(DetectedActivity.IN_VEHICLE)
    .setActivityTransition(ActivityTransition.ACTIVITY_TRANSITION_ENTER)
    .build());

transitions.add(
  new ActivityTransition.Builder()
    .setActivityType(DetectedActivity.IN_VEHICLE)
    .setActivityTransition(ActivityTransition.ACTIVITY_TRANSITION_EXIT)
    .build());

transitions.add(
  new ActivityTransition.Builder()
    .setActivityType(DetectedActivity.WALKING)
    .setActivityTransition(ActivityTransition.ACTIVITY_TRANSITION_EXIT)
    .build());

You can create an ActivityTransitionRequest object by passing the list of ActivityTransitions to the ActivityTransitionRequest class, as shown in the following example:

ActivityTransitionRequest request = new ActivityTransitionRequest(transitions);

You can register for activity transition updates by passing your instance of ActivityTransitionRequest and your PendingIntent object to the requestActivityTransitionUpdates() method. The requestActivityTransitionUpdates() method returns a Task object that you can check for success or failure, as shown in the following code example:

// myPendingIntent is the instance of PendingIntent where the app receives callbacks.
Task<Void> task =
  ActivityRecognition.getClient(context).requestActivityTransitionUpdates(request, myPendingIntent);

  task.addOnSuccessListener(
    new OnSuccessListener<Void>() {
      @Override
      public void onSuccess(Void result) {
        // Handle success
      }
    }
  );

  task.addOnFailureListener(
    new OnFailureListener() {
      @Override
      public void onFailure(Exception e) {
        // Handle error
      }
    }
  );

After successfully registering for activity transition updates, your app receives notifications in the registered PendingIntent.

Process activity transition events

When the requested activity transition occurs, you app receives an Intent callback. An ActivityTransitionResult object can be extracted from the Intent, which includes a list of ActivityTransitionEvent objects. The events are ordered in chronological order, for example, if an app requests for the IN_VEHICLE activity type on the ACTIVITY_TRANSITION_ENTER and ACTIVITY_TRANSITION_EXIT transitions, then it receives an ActivityTransitionEvent object when the user starts driving, and another one when the user transitions to any other activity.

You can implement your callback by creating a subclass of BroadcastReceiver and implementing the onReceive() method to get the list of activity transition events. For more information, see Broadcasts. The following example shows how to implement the onReceive() method:

@Override
protected void onReceive(Context context, Intent intent) {
  if (ActivityTransitionResult.hasResult(intent)) {
    ActivityTransitionResult result = ActivityTransitionResult.extractResult(intent);
    for (ActivityTransitionEvent event : result.getTransitionEvents()) {
        // chronological sequence of events....
    }
  }
}

Deregister for activity transition updates

You can deregister for activity transition updates by calling the removeActivityTransitionUpdates() method of the ActivityRecognitionClient and passing your PendingIntent object as a parameter, as shown in the following example:

// myPendingIntent is the instance of PendingIntent where the app receives callbacks.
Task<Void> task =
  ActivityRecognition.getClient(context).removeActivityTransitionUpdates(myPendingIntent);

task.addOnSuccessListener(
  new OnSuccessListener<Void>() {
    @Override
    public void onSuccess(Void result) {
      myPendingIntent.cancel();
    }
  });

task.addOnFailureListener(
  new OnFailureListener() {
    @Override
    public void onFailure(Exception e) {
      Log.e("MYCOMPONENT", e.getMessage());
    }
  });