C#

class Tree
        {
            public static TreeNode Build()
            {
                //In the real function this parses an xml file and takes less than 0.1s
                TreeNode MainNode = new TreeNode("MainNode");
                for (int i = 0; i <= 5000; i++)
                {
                    TreeNode ChildNode = new TreeNode("ChildNode" + i.ToString());
                    TreeNode SubNode = new TreeNode("SubNode");
                    ChildNode.Nodes.Add(SubNode);
                    MainNode.Nodes.Add(ChildNode);
                }
                return MainNode;
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Quick :-)
            TreeNode MainNode = Tree.Build();
            //Slow! This is the line that's taking the time
            treeView1.Nodes.Add(MainNode);
        }

public static void Build(ref TreeView treeView)
{
   TreeNode mainNode = new TreeNode("MainNode");
   List<TreeNode> childNodes = new List<TreeNode>();
   for (int i = 0; i <= 5000; i++)
   {
       TreeNode childNode = new TreeNode("ChildNode" + i.ToString());
       TreeNode subNode = new TreeNode("SubNode");
       childNode.Nodes.Add(subNode);
       childNodes.Add(childNode);
   }
   treeView.Nodes.AddRange(childNodes.ToArray());
}

public static TreeNode Build()
        {
            TreeNode mainNode = new TreeNode("MainNode");
            for (int i = 0; i <= 5000; i++)
            {
                TreeNode childNode = new TreeNode("ChildNode" + i.ToString());
                TreeNode subNode = new TreeNode("SubNode");
                childNode.Nodes.Add(subNode);
                mainNode.Nodes.Add(childNode);
            }
            return mainNode;
        }

        public static void Build(ref TreeView treeView)
        {
            TreeNode mainNode = new TreeNode("MainNode");
            List<TreeNode> childNodes = new List<TreeNode>();
            for (int i = 0; i <= 5000; i++)
            {
                TreeNode childNode = new TreeNode("ChildNode" + i.ToString());
                TreeNode subNode = new TreeNode("SubNode");
                childNode.Nodes.Add(subNode);
                childNodes.Add(childNode);
            }
            treeView.Nodes.Add(mainNode);
            treeView.Nodes[0].Nodes.AddRange(childNodes.ToArray());
            //The suggested code used the following line which missed out the mainNode but no performance difference the above
            //treeView.Nodes.AddRange(childNodes.ToArray());
        }

        private void button1_Click(object sender, EventArgs e)
        {
            treeView1.Nodes.Clear();
            treeView2.Nodes.Clear();
            listBox1.Items.Clear();
            DateTime dtBuild1Start;
            DateTime dtBuild1End;
            TimeSpan tsBuild1;
            DateTime dtBuild2Start;
            DateTime dtBuild2End;
            TimeSpan tsBuild2;
            Application.DoEvents();

            //Takes around 2100 ms
            dtBuild1Start = DateTime.Now;
            TreeNode MainNode = Build();
            //Commenting out the following line reduces to around 15 ms
            treeView1.Nodes.Add(MainNode);
            dtBuild1End = DateTime.Now;
            tsBuild1 = dtBuild1End - dtBuild1Start;
            listBox1.Items.Add("Build1 in " + tsBuild1.TotalMilliseconds.ToString() + " milliseconds");

            //Takes around 2700 ms
            dtBuild2Start = DateTime.Now;
            Build(ref treeView2);
            dtBuild2End = DateTime.Now;
            tsBuild2 = dtBuild2End - dtBuild2Start;
            listBox1.Items.Add("Build2 in " + tsBuild2.TotalMilliseconds.ToString() + " milliseconds");
        }

1. The times are very different. Granted, that is probably due to hardware differences, but I wouldn't have thought it would be that significant.
   
2. The use of AddRange should still be faster.

treeView.Nodes.Add(mainNode);
treeView.Nodes[0].Nodes.AddRange(childNodes.ToArray());

mainNode.Nodes.AddRange(childNodes.ToArray());
treeView.Nodes.Add(mainNode);

ss.mmm wrote:

'object' does not contain a definition for 'Controls'. Am I missing out some reference?

• Financial example[^]
  
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