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     private void renameToolStripMenuItem_Click(object sender, EventArgs e)
        {
            //
            //
            //
            RenameDirectory();
        }

        private void treeView1_DoubleClick(object sender, EventArgs e)
        {
            //
            //
            //
            RenameDirectory();
        }  
private void RenameDirectory()
        {
            if (treeView1.SelectedNode != null)
            {
                string sourcePath = ToolboxSubPath + "\\" + treeView1.SelectedNode.Text;
                treeView1.SelectedNode.Text = "@";
                //edit the label = true 
                treeView1.LabelEdit = true;
                if (!treeView1.SelectedNode.IsEditing)
                {
                    treeView1.SelectedNode.BeginEdit();
                }
                //save the new path name (source, destination)
                Directory.Move(sourcePath, ToolboxSubPath + "\\" + treeView1.SelectedNode.Text);
                // after edit label = false
                treeView1.LabelEdit = false;
            }
private void treeView1_AfterLabelEdit(object sender,
         System.Windows.Forms.NodeLabelEditEventArgs e)
        {
            if (e.Label != null)
            {
                if (e.Label.Length > 0)
                {
                    if (e.Label.IndexOfAny(new char[] { '@', '.', ',', '!', '?', '=', '$', '%'}) == -1)
                    {
                        // Stop editing without canceling the label change.
                        e.Node.EndEdit(false);
                    }
                    else
                    {
                        /* Cancel the label edit action, inform the user, and 
                           place the node in edit mode again. */
                        e.CancelEdit = true;
                        MessageBox.Show("Invalid tree node label.\n" +
                           "The invalid characters are: '@', '.', ',', '!', '?', '=', '$', '%'",
                           "Node Label Edit");
                        e.Node.BeginEdit();
                    }
                }
                else
                {
                    /* Cancel the label edit action, inform the user, and 
                       place the node in edit mode again. */
                    e.CancelEdit = true;
                    MessageBox.Show("Invalid tree node label.\nThe label cannot be blank",
                       "Node Label Edit");
                    e.Node.BeginEdit();
                }
            }
        }     

        }                    

1:

 private void treeView1_AfterLabelEdit                    

1:

treeView1.SelectedNode.BeginEdit();