Winform TreeView with checkboxes - only visible nodes are updated

Question

I am new here, and have searched for answers for my problem practically everywhere - to no avail. I hope that somebody here can help.

I have a WinForm application, where I use a TreeView to display the folder structure below a selected root folder. The treeview has enabled CheckBoxes. When I check or uncheck a checkbox on a TreeNode, any visible nodes below that TreeNode changes as well - so far so good.

The problem is, that when I expand the nodes further, then the new visible nodes are not updated to the correct state.

I used the following recursive routine to perform the update:

    private void CheckAllChildNodes(TreeNode treeNode, bool nodeChecked)
    {
        foreach (TreeNode node in treeNode.Nodes)
        {
            node.Checked = nodeChecked;
            if (node.Nodes.Count > 0)
            {
                // If the current node has child nodes, call the
                // CheckAllChildNodes method recursively.
                CheckAllChildNodes(node, nodeChecked);
            }
        }
    }

It is called from this event handler:

    private void FileTreeView_AfterCheck(object sender, TreeViewCancelEventArgs e)
    {
        // The code only executes if the user caused the checked state to change.
        if (e.Action == TreeViewAction.ByMouse)
        {
            if (e.Node.Nodes.Count > 0)
            {
                // Calls the CheckAllChildNodes method, passing in the current
                // checked value of the TreeNode whose checked state changed.
                CheckAllChildNodes(e.Node, e.Node.Checked);
            }
        }
    }

It seems that the recursive function only cares about TreeNodes that are visible at the time of execution.

If anyone can give a clue of what is wrong, and what can be done to correct it, it will be greatly appreciated.

Thanks in advance.

Best regards,

L. Hummel

Answer 1

Two things. One, you don't need the "if (e.Node.Nodes.Count > 0)" in either. That is a little redundant as if there are 0 nodes when you call a "foreach", it immediately passes out of the loop.

Two, the easiest solution may be to just wire into the AfterExpand method, and when the node gets expanded, set the children then:

private void FileTreeView_AfterExpandobject sender, TreeViewEventArgs e)
{
    // Calls the CheckAllChildNodes method, passing in the current
    // checked value of the TreeNode whose checked state changed.
    CheckAllChildNodes(e.Node, e.Node.Checked);        
}

Also, are you sure you want TreeViewCancelEventArgs in your event methods, and not just TreeViewEventArgs?