insert method Null safety

void insert(
  1. OverlayEntry entry,
  2. {OverlayEntry? below,
  3. OverlayEntry? above}
)

Insert the given entry into the overlay.

If below is non-null, the entry is inserted just below below. If above is non-null, the entry is inserted just above above. Otherwise, the entry is inserted on top.

It is an error to specify both above and below.

Implementation

void insert(OverlayEntry entry, { OverlayEntry? below, OverlayEntry? above }) {
  assert(_debugVerifyInsertPosition(above, below));
  assert(!_entries.contains(entry), 'The specified entry is already present in the Overlay.');
  assert(entry._overlay == null, 'The specified entry is already present in another Overlay.');
  entry._overlay = this;
  setState(() {
    _entries.insert(_insertionIndex(below, above), entry);
  });
}