Selecting child view at index using Espresso

Question

With Espresso when using a custom widget view with child image views, which Matcher type can I use to select the nth child? Example:

+--------->NumberSlider{id=2131296844, res-name=number_slider, visibility=VISIBLE, width=700, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=false, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=10.0, y=0.0, child-count=7}
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+---------->NumberView{id=-1, visibility=VISIBLE, width=99, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=true, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=0.0, y=0.0}
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+---------->NumberView{id=-1, visibility=VISIBLE, width=100, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=true, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=99.0, y=0.0}
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+---------->NumberView{id=-1, visibility=VISIBLE, width=100, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=true, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=199.0, y=0.0}
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+---------->NumberView{id=-1, visibility=VISIBLE, width=100, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=true, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=299.0, y=0.0}
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+---------->NumberView{id=-1, visibility=VISIBLE, width=100, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=true, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=399.0, y=0.0}
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+---------->NumberView{id=-1, visibility=VISIBLE, width=100, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=true, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=499.0, y=0.0}
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+---------->NumberView{id=-1, visibility=VISIBLE, width=100, height=95, has-focus=false, has-focusable=false, has-window-focus=true, is-clickable=true, is-enabled=true, is-focused=false, is-focusable=false, is-layout-requested=false, is-selected=false, root-is-layout-requested=false, has-input-connection=false, x=599.0, y=0.0}

Answer 1

 public static Matcher<View> nthChildOf(final Matcher<View> parentMatcher, final int childPosition) {
    return new TypeSafeMatcher<View>() {
      @Override
      public void describeTo(Description description) {
        description.appendText("with "+childPosition+" child view of type parentMatcher");
      }

      @Override
      public boolean matchesSafely(View view) {
        if (!(view.getParent() instanceof ViewGroup)) {
          return parentMatcher.matches(view.getParent());
        }

        ViewGroup group = (ViewGroup) view.getParent();
        return parentMatcher.matches(view.getParent()) && group.getChildAt(childPosition).equals(view);
      }
    };
  }

To use it

onView(nthChildOf(withId(R.id.parent_container), 0)).check(matches(withText("I am the first child")));