how to sort the child nodes of treeView

Question

I want to sort a given TreeView child nodes in alphabetical order.

Suppose my tree View is like this:

• firstNode1

  • secondNode1
  • thirdNode1
  • thirdNode2
  • thirdNode3 ...

• firstNode2

  • secondNode1
  • thirdNode1
  • thirdNode2
  • thirdNode3 ...

I want to sort the nodes in secondNodes of every firstNode.

How can I do it? - I have red about Custom Comparer but cant understand how to use it in my case.

Answer 1

For a normal alphabetical sort simply call the built-in sort:

treeView1.Sort();

and you are good.

But sometimes this is not good enough. Then you need to write a custom sorter. This is really simple; all it needs to provide is an int for the result of <, == or >, i.e. return -1, 0 or 1 respectively. Often the built-in comparers will do after massaging the data a bit..

Here is an example of a custom sorter. This is a simple class implementing the IComparer interface, which has just one method..

---

It prepares the two node texts for my custom comparison before calling the regular string Compare method.

The preparation inserts a large number of zeroes to pad a trailing number to a constant length.

It is just an example but will sort e.g. the default names from the designer numerically/chronologically.

---

public class NodeSorter : System.Collections.IComparer
{
    public NodeSorter() { }

    public int Compare(object x, object y)
    {
        TreeNode tx = x as TreeNode;
        TreeNode ty = y as TreeNode;

        string s1 = tx.Text;
        while (s1.Length > 0 && Char.IsDigit(s1.Last())) s1 = s1.TrimEnd(s1.Last());
        s1 = s1 + tx.Text.Substring(s1.Length).PadLeft(12, '0');

        string s2 = tx.Text;
        while (s2.Length > 0 && Char.IsDigit(s2.Last())) s2 = s2.TrimEnd(s2.Last());
        s2 = s2 + ty.Text.Substring(s2.Length).PadLeft(12, '0');

        return string.Compare(s1, s2);
    }
}

You call it by assigning it and then calling sort:

treeView1.TreeViewNodeSorter = new NodeSorter();
treeView1.Sort();

Result:

This is a slightly modified version of the MSDN TreeNodeSorter example. Besides the changed logic do note:

• The example is old and doesn't qualify the IComparer interface properly. With the advent of generics we usually have a using System.Collections.Generic; clause and this will hide the non-generic IComparer interface, leading to compiler errors, complaining about the missing type arguments.

Adding the qualification takes care of that..:

public class NodeSorter : System.Collections.IComparer