Canceling Jobs

Canceling Jobs:

It is a common requirement that sometimes you notice a Job will not be needed anymore, like when a user leaves an activity or a user cancel an operation.

To achieve this, you can use job tags to identify your Jobs and later reference them to cancel using JobManager#cancelJobs or JobManager#cancelJobsInBackground.

Note that if a job is already running when cancel request arrives, JobManager will wait until Job#onRun method finishes (so no thread interrupts to stop the job). If you have a long running onRun method, you can check Job#isCancelled and if it returns true, just throw an exception to immediately stop the Job.

Case Study: Canceling Jobs of an Activity

Here is an example on how you could cancel all jobs created for an Activity when it becomes invisible. This sample uses onStart & onStop tuple, but you could as well use onCreate and onDestroy.

public class BaseActivity extends Activity {
  ...
  // a random string identifier that is generated when Activity becomes visible
  private String sessionId; 
  // preferably injected
  private JobManager jobManager; 

  public String getSessionId() {
    return sessionId;
  }

  @Override
  protected void onStart() {
    super.onStart();
    sessionId = UUID.randomUUID().toString();
  }

  @Override
  protected void onStop() {
    super.onStop();
    jobManager.cancelJobsInBackground(null, TagConstraint.ANY, sessionId);
  }
}

Now, in an activity that extends this BaseActivity, you can create jobs that will automatically be cancelled when Activity goes to background as follows:

abstract class ActivityBoundJob extends Job {
  public ActivityBoundJob(BaseActivity activity, Params params) {
    super(params.addTags(activity.getSessionId()));
  }
}