preventing duplicates when inserting nodes to treeview control

Question

I want to create a hierarchical view of strings based on first two characters.

If the strings are: AAAA,AAAA,BBDD,AABB,AACC,BBDD,BBEE

I want to reate a treeview that looks like this:

AA  
  AAAA  
  AABB
  AACC 
BB
  BBDD
  BBEE

I currently have some code that looks like this (inside a loop over the strings):

    TreeNode pfxNode;

    if (treeView1.Nodes[pfx]!=null) {
        pfxNode = treeView1.Nodes[pfx];
    }
    else {
        pfxNode = treeView1.Nodes.Add(pfx);
    }

    if (!pfxNode.Nodes.ContainsKey(string)) {
        pfxNode.Nodes.Add(string, string + " some info");
    }

For some reason this ends up with multiple "AA" nodes at the top level.
What am I missing?

please no pre-filtering of strings I want to be able to check if a specific treenode exists based on its key.

thanks

score 2 · Accepted Answer · answered Jun 09 '11 at 21:05

2

else {
    pfxNode = treeView1.Nodes.Add(pfx);
}

There's your mistake, you are forgetting to set the key of the tree node. So the next ContainsKey() won't find it. Fix:

    pfxNode = treeView1.Nodes.Add(pfx, pfx);

answered Jun 09 '11 at 21:05

Hans Passant

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This is definately what I was missing. I expected that pfx would also become the key when a single string is provided. thanks. – epeleg Jun 11 '11 at 14:01

Magnus · Answer 2 · 2011-06-09T20:59:29.620

0

Use this:

var q = from s in arr
        group s by s.Substring(0, 2) into g
        select new
        {
            Parent = g.Key,
            Children = g.Select (x => x).Distinct()
        };

foreach (var item in q)
{
    var p = new TreeNode(item.Parent);
    TreeView1.Nodes.Add(p);
    foreach (var item2 in item.Children)
        p.Nodes.Add(new TreeNode(item2));
}

edited Jun 09 '11 at 20:59

answered Jun 09 '11 at 20:49

Magnus

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although the answer provided by @Hans Passant solved my Problem I am still interested in your answer as well. This is LINQ syntax - right? could you provide some details on how this should work ? also is there any performance or other advantage to this syntax? – epeleg Jun 11 '11 at 14:05
also I was not able to run add this code to my program, it does not seem to know what var is and keeps saying that many ;'s are missing along this text block. should I install something to make this work ? – epeleg Jun 11 '11 at 14:08
@epeleg You need .NET >= 3.5 for Linq and `var` key word to work. As for performance linq `group by` and `distinct` operation are pretty good. – Magnus Jun 11 '11 at 15:16

preventing duplicates when inserting nodes to treeview control

2 Answers2