void OnEnable () {
UpdatePosition();
if (root == null) {
root = this;
} else {
next = root;
root.prev = this;
root = this;
}
}
void OnDisable () {
if (root == this) {
root = next;
if (root != null) root.prev = null;
} else {
if (prev != null) prev.next = next;
if (next != null) next.prev = prev;
}
prev = null;
next = null;
}