collapseAll method
void
collapseAll()
关闭所有 node
Implementation
void collapseAll() {
assert(_isInitialized);
if (_nodes != null) {
List<EasyTreeNode<E>> result =
_nodes!.where((element) => element.level == 0).toList();
for (EasyTreeNode<E> node in result)
if (node.expanded) this.collapse(node);
toggleNodeExpanded(_initialNodes, false);
}
}