DefiningInitialFragmentWithState.java 文件源码

private static Matcher<View> childAtPosition(
        final Matcher<View> parentMatcher, final int position) {

    return new TypeSafeMatcher<View>() {
        @Override
        public void describeTo(Description description) {
            description.appendText("Child at position " + position + " in parent ");
            parentMatcher.describeTo(description);
        }

        @Override
        public boolean matchesSafely(View view) {
            ViewParent parent = view.getParent();
            return parent instanceof ViewGroup && parentMatcher.matches(parent)
                    && view.equals(((ViewGroup) parent).getChildAt(position));
        }
    };
}