Expand selected node after refresh TreeView in C#

Question

I have a treeview with many items

When I expand an item and its childs and after I called refresh method, that expanded item childs becomes collapsed.

Can you give me an idea how to store the selected node and after refresh, to call the Expand method again...

I tried :

 TreeNode selectedNode = new TreeNode();
 TreeNode selectedNode = SelectedTreeNode();  //method which takes selected node from TV
 RestoreFolderTreeWithLastSelectedItem(); //method which initialise treeview object
 //here I want to call Expand() method but it not exists to TreeNode.

For treeview, I used Windows.Controls.treeView namespace I am beginner... Thank you

I will explain you via images

I expanded all items:

If I press F5 or call Refresh function (RestoreFolderTreeWithLastSelectedItem();) then they will be collapsed like as:

instead of first image...

Answer 1

I'm using this with a WinForms TreeView. It saves the nodes expanded state between refreshes:

// Save the path of the expanded tree branches
var savedExpansionState = treeView1.Nodes.GetExpansionState();

treeView1.BeginUpdate();

// TreeView is populated
// ...

// Once it is populated, we need to restore expanded nodes
treeView1.Nodes.SetExpansionState(savedExpansionState);

treeView1.EndUpdate();

Here is the code to achieve this:

public static class TreeViewExtensions
{
    public static List<string> GetExpansionState(this TreeNodeCollection nodes)
    {
        return nodes.Descendants()
                    .Where(n => n.IsExpanded)
                    .Select(n => n.FullPath)
                    .ToList();
    }

    public static void SetExpansionState(this TreeNodeCollection nodes, List<string> savedExpansionState)
    {
        foreach (var node in nodes.Descendants()
                                  .Where(n => savedExpansionState.Contains(n.FullPath)))
        {
            node.Expand();
        }
    }

    public static IEnumerable<TreeNode> Descendants(this TreeNodeCollection c)
    {
        foreach (var node in c.OfType<TreeNode>())
        {
            yield return node;

            foreach (var child in node.Nodes.Descendants())
            {
                yield return child;
            }
        }
    }
}