Compiler Error CS1061 | Microsoft Docs[
^] occurs when you try to call a method or access a class member that does not exist.
Note that
this.CheckAllChildNodes
refer to Form class and you probably didn't define such of method. Add below methd to find out if error dissapear.
private void CheckAllChildNodes(TreeNode treeNode, bool nodeChecked)
{
foreach(TreeNode node in treeNode.Nodes)
{
node.Checked = nodeChecked;
if(node.Nodes.Count > 0)
{
this.CheckAllChildNodes(node, nodeChecked);
}
}
}