How to count RecyclerView items with Espresso

Question

Using Espresso and Hamcrest,

How can I count items number available in a recyclerView?

Exemple: I would like check if 5 items are displaying in a specific Re

Answer 1

Adding a bit of syntax sugar to the @Stephane's answer.

public class RecyclerViewItemCountAssertion implements ViewAssertion {
    private final Matcher matcher;

    public static RecyclerViewItemCountAssertion withItemCount(int expectedCount) {
        return withItemCount(is(expectedCount));
    }

    public static RecyclerViewItemCountAssertion withItemCount(Matcher matcher) {
        return new RecyclerViewItemCountAssertion(matcher);
    }

    private RecyclerViewItemCountAssertion(Matcher matcher) {
        this.matcher = matcher;
    }

    @Override
    public void check(View view, NoMatchingViewException noViewFoundException) {
        if (noViewFoundException != null) {
            throw noViewFoundException;
        }

        RecyclerView recyclerView = (RecyclerView) view;
        RecyclerView.Adapter adapter = recyclerView.getAdapter();
        assertThat(adapter.getItemCount(), matcher);
    }
}

Usage:

    import static your.package.RecyclerViewItemCountAssertion.withItemCount;

    onView(withId(R.id.recyclerView)).check(withItemCount(5));
    onView(withId(R.id.recyclerView)).check(withItemCount(greaterThan(5)));
    onView(withId(R.id.recyclerView)).check(withItemCount(lessThan(5)));
    // ...