Treeview - iterate through all nodes, stop at first visible

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I'm having a mental block right now, this can't be that hard.
I have a function which should get the last visible node in the TreeView. First I want to go to the first visible node and then second from there on go as long as node.IsVisible().

What I have tried:

C#

public TreeNode GetLastVisibleNode()
    {
        var node = treeControl1.Nodes.Cast<TreeNode>().Where(x => x.IsVisible).FirstOrDefault();
        TreeNode retVal = node;
        while (node != null && node.IsVisible)
        {
            if (!node.IsSelected)
                retVal = node;
            node = node.NextVisibleNode;
        }
        return retVal;
    }

I made it to iterate to the last visible node when I have the first visible (HOORAY) but my approach of getting the first visible is WRONG (OHHHHH!)
I noticed that treeControl1.Nodes only gives me the parent nodes but obvioulsy I want to get the first visible node of all nodes.
I also know that I probably need a recursive method but as I said in the beginning, I'm having a mental block right now and want to have this fixed quite soon :(

Posted 19-Jul-18 2:58am

Markus Rechberger

Updated 19-Jul-18 4:39am

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Eric Lynch · Accepted Answer · 2018-07-19T03:10:00

The following should work:

private static TreeNode FindFirstVisible(TreeNodeCollection nodes)
{
  foreach (TreeNode node in nodes)
  {
    if (node.IsVisible)
      return node;

    TreeNode first = FindFirstVisible(node.Nodes);
    if (first != null)
      return first;
  }

  return null;
}

To call, use as follows:

TreeNode first = FindFirstVisible(tree.Nodes);

For completeness, you may also want to check out (which is slightly different from what you ask):
TreeView.TopNode Property (System.Windows.Forms) | Microsoft Docs[^]

Actually, thinking a bit longer, you shouldn't even need to dig into the tree. I believe for a child node to be visible the parent must be visible. So, I think you either must have a top level node visible, or no nodes are visible. So, the following should work:

private static TreeNode FindFirstVisible(TreeNodeCollection nodes) =>
  nodes.Cast<TreeNode>().FirstOrDefault(node => node.IsVisible);

Based on subsequent information, and if you are concerned about scrolling, the following methods will let you select the last partially or fully visible node. Using NextVisibleNode will not consider whether the node has scrolled out of range.

private TreeNode GetFirstVisibleNode(TreeView tree, bool includePartial)
{
  if (!includePartial)
    return tree.TopNode;

  Rectangle treeBounds = tree.ClientRectangle;
  return tree.Nodes.Cast<TreeNode>()
    .FirstOrDefault(node => node.IsVisible &&
      treeBounds.Contains(node.Bounds));
}

private TreeNode GetLastVisibleNode(TreeView tree, bool includePartial)
{
  TreeNode last = GetFirstVisibleNode(tree, includePartial);
  Rectangle treeBounds = tree.Bounds;

  for (TreeNode node = last; node != null; node = node.NextVisibleNode)
  {
    if (includePartial)
    {
      if (!treeBounds.IntersectsWith(node.Bounds))
        break;
    }
    else
    {
      if (!treeBounds.Contains(node.Bounds))
        break;
    }

    last = node;
  }

  return last;
}

Markus Rechberger · Accepted Answer · 2018-07-19T04:08:00

C#

public TreeNode GetLastVisibleNode()
        {
            return treeControl1.Nodes.Cast<TreeNode>().Select(GetLastVisibleNode).
                            LastOrDefault(first => first != null);
        }

TreeNode GetLastVisibleNode(TreeNode parentNode) =>
        parentNode.IsVisible
             ? parentNode
             : parentNode.Nodes.Cast<TreeNode>().Select(GetLastVisibleNode).
                      LastOrDefault(childFirstNode => childFirstNode != null);

Someone answered the same question I asked here

Markus Rechberger · Accepted Answer · 2018-07-19T04:39:00

I was told in the comments that TreeView.TopNode gets me the first visible node.

From there on I just iterated through the list as long as node.IsVisible and node != null.

C#

public TreeNode GetLastVisibleNode()
        {
            TreeNode node = treeControl1.TopNode;
            TreeNode retVal;
            do
            {
                retVal = node;
                node = node.NextVisibleNode;
            } while (node != null && node.IsVisible);

            return retVal;
        }

Treeview - iterate through all nodes, stop at first visible

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