Espresso idlingResource - how to register?

Issue

in the @Before function of one of my tests i am trying to register espresso idlingResource but i keep getting error that it needs to be run off the main thread. here is what i have so far:

 @Before
    public void setUp() throws Exception {
        mIntentsTestRule.getActivity().sharedPrefRepo.clearAll();

        new Thread(){
            @Override
            public void run() {
                super.run();
                IdlingResource loadingDialogIdlingResource = new LoadingDialogIdlingResource();
                IdlingRegistry.getInstance().register(loadingDialogIdlingResource);
            }
        }.start();

}

but this kind of makes no sense. im registering these things on another thread and yet i'll continue running my tests before it completes ? what is the way to really register these things ? i have created a unregister function as well in teardown which looks like this:

@After
    public void tearDown() throws Exception {
        //handle any clean up
        mIntentsTestRule.getActivity().sharedPrefRepo.clearAll();
        freeIdlingResources();
    mIntentsTestRule.getActivity().finish();
    }

the error is below if i do not use a thread:

java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.RuntimeException: This method can not be called from the main application thread
at android.support.test.espresso.base.IdlingResourceRegistry.runSynchronouslyOnMainThread(IdlingResourceRegistry.java:314)
at android.support.test.espresso.base.IdlingResourceRegistry.sync(IdlingResourceRegistry.java:90)
at android.support.test.espresso.Espresso.onView(Espresso.java:69)

please note: The former Espresso.registerIdlingResources() method has been deprecated in by IdlingRegistry via getInstance().register().

update: here is my idlresource code:

public class LoadingDialogIdlingResource implements IdlingResource {
      private ResourceCallback resourceCallback;
      private boolean isIdle;

      @Override
      public String getName() {
          return LoadingDialogIdlingResource.class.getName();
      }

      @Override
      public boolean isIdleNow() {
          if (isIdle) return true;

          Activity activity = getCurrentActivity();
          if (activity == null) return false;

          Fragment f = activity.getFragmentManager().findFragmentByTag(ProgressDialogFragment.class.getName());
          isIdle = f == null;
          if (isIdle) {
              resourceCallback.onTransitionToIdle();
          }
          return isIdle;
      }

      public Activity getCurrentActivity() {
          final Activity[] currentActivity = {null};

          InstrumentationRegistry.getInstrumentation().runOnMainSync(new Runnable(){
              public void run(){
                  Collection<Activity> resumedActivity = ActivityLifecycleMonitorRegistry.getInstance().getActivitiesInStage(Stage.RESUMED);
                  Iterator<Activity> it = resumedActivity.iterator();
                  currentActivity[0] = it.next();
              }
          });
          return currentActivity[0];
      }

      @Override
      public void registerIdleTransitionCallback(
              ResourceCallback resourceCallback) {
          this.resourceCallback = resourceCallback;
      }
  }

Solution

The problem was in this block of code:

public Activity getCurrentActivity() {
    final Activity[] currentActivity = {null};

    InstrumentationRegistry.getInstrumentation().runOnMainSync(new Runnable(){
        public void run(){
            Collection<Activity> resumedActivity = ActivityLifecycleMonitorRegistry.getInstance().getActivitiesInStage(Stage.RESUMED);
            Iterator<Activity> it = resumedActivity.iterator();
            currentActivity[0] = it.next();
        }
    });
    return currentActivity[0];
}

Calling runOnMainSync is forbidden here. I resolved the issue by simply passing in the fragment manager into the constructor.

Answered By - j2emanue