Question

My TreeView control is displaying the structure of some selected hard disk drive. In my addToParentNode, I make a call from after the tree view is expanded. But when I pass the node from one method to another, an “Object reference not set to an instance of an object” exception is thrown.

void addToParentNode(TreeNode childNodes)
{
    DirectoryInfo getDir = new DirectoryInfo(childNodes.Tag.ToString());
    DirectoryInfo[] dirList = getDir.GetDirectories();
    foreach (DirectoryInfo dir in dirList)
    {
        TreeNode parentNode = new TreeNode();
        parentNode.Text = dir.Name;
        parentNode.Tag = dir.FullName;
        childNodes.Nodes.Add(parentNode);
    }
}

private void tv_fileExplore_AfterExpand(object sender, TreeViewEventArgs e)
{
    foreach (TreeNode item in e.Node.Nodes)
    {
        addToParentNode(item);
    }
}

Can someone point me in the right direction?

Answer 1

According to the comments on your question, the Tag property of a tree node is null.

You are assigning a non-null value to every tree node in your addToParentNode method, but somewhere, there must be a start and you must be creating a root node. Therefore, that root node apparently has its Tag property still set to null.