Is it possible to use Espresso's IdlingResource to wait until a certain view appears?

Question

In my test I have a stage where after pressing a button application does a lot of asynchronous calculations and requests to the cloud service, after which it displays a certain view.

Is it possible to use Espresso's IdlingResource implementation to wait until a certain view appears?

I've read an answers here and comments seems to suggest that you can use IdlingResource instead, but I don't understand how. Espresso does not seem to have any built-in way to handle long operations, but having to write your own waiting loops feels like a hack.

Any way to solve this or should I just do as the answer in the linked thread suggests?

Answer 1

Atte Backenhof's solution has a small bug (or maybe I don't fully understand the logic).

getView should return a null instead of throwing an exception to make IdlingResources work.

Here's a Kotlin solution with the fix:

/**
 * @param viewMatcher The matcher to find the view.
 * @param idleMatcher The matcher condition to be fulfilled to be considered idle.
 */
class ViewIdlingResource(
    private val viewMatcher: Matcher<View?>?,
    private val idleMatcher: Matcher<View?>?
) : IdlingResource {

    private var resourceCallback: IdlingResource.ResourceCallback? = null

    /**
     * {@inheritDoc}
     */
    override fun isIdleNow(): Boolean {
        val view: View? = getView(viewMatcher)
        val isIdle: Boolean = idleMatcher?.matches(view) ?: false
        if (isIdle) {
            resourceCallback?.onTransitionToIdle()
        }
        return isIdle
    }

    /**
     * {@inheritDoc}
     */
    override fun registerIdleTransitionCallback(resourceCallback: IdlingResource.ResourceCallback?) {
        this.resourceCallback = resourceCallback
    }

    /**
     * {@inheritDoc}
     */
    override fun getName(): String? {
        return "$this ${viewMatcher.toString()}"
    }

    /**
     * Tries to find the view associated with the given [<].
     */
    private fun getView(viewMatcher: Matcher<View?>?): View? {
        return try {
            val viewInteraction = onView(viewMatcher)
            val finderField: Field? = viewInteraction.javaClass.getDeclaredField("viewFinder")
            finderField?.isAccessible = true
            val finder = finderField?.get(viewInteraction) as ViewFinder
            finder.view
        } catch (e: Exception) {
            null
        }
    }

}

/**
 * Waits for a matching View or throws an error if it's taking too long.
 */
fun waitUntilViewIsDisplayed(matcher: Matcher<View?>) {
    val idlingResource: IdlingResource = ViewIdlingResource(matcher, isDisplayed())
    try {
        IdlingRegistry.getInstance().register(idlingResource)
        // First call to onView is to trigger the idler.
        onView(withId(0)).check(doesNotExist())
    } finally {
        IdlingRegistry.getInstance().unregister(idlingResource)
    }
}

Usage in your UI tests:

    @Test
    fun testUiNavigation() {
        ...
        some initial logic, navigates to a new view
        ...
        waitUntilViewIsDisplayed(withId(R.id.view_to_wait_for))
        ...
        logic on the view that we waited for
        ...
    }

Important update: default timeout for the IdlingResources is 30 seconds, they don't wait forever. To increase a timeout you need to call it in @Before method for example: IdlingPolicies.setIdlingResourceTimeout(3, TimeUnit.MINUTES)

Answer 2

I took inspiration from Anatolii, but instead of using methods from the View.class I still only use ViewMatchers.

/**
 * {@link IdlingResource} that idles until a {@link View} condition is fulfilled.
 */
public class ViewIdlingResource implements IdlingResource {

    private final Matcher<View>    viewMatcher;
    private final Matcher<View>    idleMatcher;
    private       ResourceCallback resourceCallback;

    /**
     * Constructor.
     *
     * @param viewMatcher The matcher to find the view.
     * @param idlerMatcher The matcher condition to be fulfilled to be considered idle.
     */
    public ViewIdlingResource(final Matcher<View> viewMatcher, Matcher<View> idlerMatcher) {
        this.viewMatcher = viewMatcher;
        this.idleMatcher = idlerMatcher;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean isIdleNow() {
        View view = getView(viewMatcher);
        boolean isIdle = idleMatcher.matches(view);

        if (isIdle && resourceCallback != null) {
            resourceCallback.onTransitionToIdle();
        }

        return isIdle;
    }

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

    /**
     * {@inheritDoc}
     */
    @Override
    public String getName() {
        return this + viewMatcher.toString();
    }

    /**
     * Tries to find the view associated with the given {@link Matcher<View>}.
     */
    private static View getView(Matcher<View> viewMatcher) {
        try {
            ViewInteraction viewInteraction = onView(viewMatcher);
            Field finderField = viewInteraction.getClass().getDeclaredField("viewFinder");
            finderField.setAccessible(true);
            ViewFinder finder = (ViewFinder) finderField.get(viewInteraction);
            return finder.getView();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

And how to use the idler in your test case, I pass the ViewMatchers.isDisplayed() to be my expected condition in the idler.

private void waitUntilViewIsDisplayed(Matcher<View> matcher) {
        IdlingResource idlingResource = new ViewIdlingResource(matcher, isDisplayed());
        try {
            IdlingRegistry.getInstance().register(idlingResource);
            // First call to onView is to trigger the idler.
            onView(withId(0)).check(doesNotExist());
        } finally {
            IdlingRegistry.getInstance().unregister(idlingResource);
        }
    }

With this you can pass any Matcher.class to the ViewIdlingResource constructor to be the required condition for the view found by the viewMatcher parameter.

Answer 3

Your IdlingResource could look like this:

import android.support.test.espresso.IdlingResource;
import android.support.test.espresso.ViewFinder;
import android.support.test.espresso.ViewInteraction;
import android.view.View;

import org.hamcrest.Matcher;

import java.lang.reflect.Field;

import static android.support.test.espresso.Espresso.onView;

public class ViewShownIdlingResource implements IdlingResource {

    private static final String TAG = ViewShownIdlingResource.class.getSimpleName();

    private final Matcher<View> viewMatcher;
    private ResourceCallback resourceCallback;

    public ViewShownIdlingResource(final Matcher<View> viewMatcher) {
        this.viewMatcher = viewMatcher;
    }

    @Override
    public boolean isIdleNow() {
        View view = getView(viewMatcher);
        boolean idle = view == null || view.isShown();

        if (idle && resourceCallback != null) {
            resourceCallback.onTransitionToIdle();
        }

        return idle;
    }

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

    @Override
    public String getName() {
        return this + viewMatcher.toString();
    }

    private static View getView(Matcher<View> viewMatcher) {
        try {
            ViewInteraction viewInteraction = onView(viewMatcher);
            Field finderField = viewInteraction.getClass().getDeclaredField("viewFinder");
            finderField.setAccessible(true);
            ViewFinder finder = (ViewFinder) finderField.get(viewInteraction);
            return finder.getView();
        } catch (Exception e) {
            return null;
        }
    }
}

Then, you could create a helper method waiting for your view:

public void waitViewShown(Matcher<View> matcher) {
    IdlingResource idlingResource = new ViewShownIdlingResource(matcher);///
    try {
        IdlingRegistry.getInstance().register(idlingResource);
        onView(matcher).check(matches(isDisplayed()));  
    } finally {
        IdlingRegistry.getInstance().unregister(idlingResource);
    }    
}

Finally, in your test:

@Test
public void someTest() {
    waitViewShown(withId(R.id.<some>));

    //do whatever verification needed afterwards    
} 

You could improve this example by making IdlingResource wait for any condition, not just for the visibility one.