material-components/material-components-android · error · IllegalArgumentException

> resourceName < is not a valid ancestor

Error message

> resourceName < is not a valid ancestor

What it means

TransitionUtils.findAncestorById (around TransitionUtils.java:285) walks up the view hierarchy from a starting view looking for an ancestor with the given id; if the root is reached without a match, it throws IllegalArgumentException naming the resolved resource ("<name> is not a valid ancestor"). The id must belong to a parent/ancestor in the same inflated hierarchy — sibling ids, descendant ids, or ids from other fragments simply will not be found.

Source

Thrown at lib/java/com/google/android/material/transition/TransitionUtils.java:285

      return descendant;
    }
    return findAncestorById(view, viewId);
  }

  static View findAncestorById(View view, @IdRes int ancestorId) {
    String resourceName = view.getResources().getResourceName(ancestorId);
    while (view != null) {
      if (view.getId() == ancestorId) {
        return view;
      }
      ViewParent parent = view.getParent();
      if (parent instanceof View) {
        view = (View) parent;
      } else {
        break;
      }
    }
    throw new IllegalArgumentException(resourceName + " is not a valid ancestor");
  }

  static RectF getRelativeBounds(View view) {
    return new RectF(view.getLeft(), view.getTop(), view.getRight(), view.getBottom());
  }

  static Rect getRelativeBoundsRect(View view) {
    return new Rect(view.getLeft(), view.getTop(), view.getRight(), view.getBottom());
  }

  static RectF getLocationInWindow(View view) {
    int[] location = new int[2];
    view.getLocationInWindow(location);
    int left = location[0];
    int top = location[1];
    int right = left + view.getWidth();
    int bottom = top + view.getHeight();
    return new RectF(left, top, right, bottom);

View on GitHub (pinned to ac7e18efee)

Solutions

1. Verify the id passed as the ancestor belongs to a real parent/ancestor of the start view in the same inflated tree.
2. Run the lookup only after the view is attached (do it in onViewCreated/onAttachedToWindow, not in inflate-time callbacks).
3. If the target is in a different hierarchy, restructure so both views share one common ancestor before starting the transform.

Example fix

// before
transform.setTargetViewId(R.id.wrong_container); // not an ancestor of startView

// after
// ensure R.id.real_container wraps startView in the same layout
transform.setTargetViewId(R.id.real_container);

static View findAncestorOrNull(View start, @IdRes int ancestorId) {
  View v = start;
  while (v != null) {
    if (v.getId() == ancestorId) return v;
    ViewParent p = v.getParent();
    v = p instanceof View ? (View) p : null;
  }
  return null; // caller decides: skip transform or fail with its own message
}
View target = findAncestorOrNull(startView, R.id.target_container);
if (target != null) transform.setTargetView(target); else Log.w(TAG, "ancestor missing; skipping transform");

static boolean hasAncestorWithId(View v, @IdRes int id) {
  for (ViewParent p = v.getParent(); p != null; p = p.getParent()) {
    if (p instanceof View && ((View) p).getId() == id) return true;
  }
  return false;
}

When it happens

Trigger: Passing a targetViewResId to MaterialContainerTransform that is not actually an ancestor of the transitioned view; referencing a view id in a different fragment or a sibling container; calling findAncestorById before the view is attached to its full hierarchy (view detached or not yet added).

Common situations: Container transform configured with the wrong resource id (copy-paste of a target id); fragment view hierarchies where the "ancestor" lives in the activity layout but the start view is in a fragment that is not yet attached; RecyclerView item views whose assumed ancestor id exists only in some view holders.

Related errors

• > resourceName < is not a valid ancestor
• MaterialSplitButton can only hold MaterialButtons.
• MaterialSplitButton can only hold two MaterialButtons.
• We already have an EditText, can only have one
• The view is not a child of CoordinatorLayout

AI-assisted analysis of material-components/material-components-android@ac7e18efee (2026-08-14). Data as JSON: /api/errors/b81002bd02020cd3. Report an issue: GitHub.