How to expand first level children only of Treeview

Question

I want to show all children of the first level on the treeview by default. And then expand all children of those on click.

Answer 1

Try:

foreach (TreeNode tn in treeView1.Nodes) {
  tn.Expand();
}

When adding nodes during runtime, you can just check the level and expand, if needed:

private void ShouldAutoExpand(TreeNode tn) {
  if (tn.Level == 0)
    tn.Expand();
}

There is no NodeAdded event you can hook into to check that automatically. You would have to determine yourself whether or not a node should be expanded "by default".

Update:

From your comment, it seems like you want to have all level 0 nodes expanded, but then expand all child nodes of level 1 when you expand them.

Try subscribing to the BeforeExpand event with this code:

private void treeView1_BeforeExpand(object sender, TreeViewCancelEventArgs e) {
  treeView1.BeforeExpand -= treeView1_BeforeExpand;
  if (e.Node.Level == 1) {
    e.Node.ExpandAll();
  }
  treeView1.BeforeExpand += treeView1_BeforeExpand;
}

Answer 2

you can try something like this.. you will have to change the example to fit your own code since you neglected to paste any code that you have or attempted

private void addChildNode_Click(object sender, EventArgs e) 
{
  var childNode = textBox1.Text.Trim();
  if (!string.IsNullOrEmpty(childNode)) {
    TreeNode parentNode = treeView2.SelectedNode ?? treeView2.Nodes[0];
    if (parentNode != null) {
      parentNode.Nodes.Add(childNode);
      treeView2.ExpandAll();
    }
  }
}

Answer 3

if you want a recursive, try this:

void expAll(TreeNode node)
{
   node.Expand();
   foreach(TreeNode i in node.Nodes)
   {
       expAll(i);
   }
}