Question

This is the feature i want to implement:

1. check a tree node by click mouse as normal, user can multiple select.

2. when user hold Ctrl+ mouse, i want the tree node which mouse clicked to be checked and all other nodes are unchecked.

I have a version but it is not elegant:

Any suggestions?

If you want to test the code, replace TreeViewAdv and TreeNodeAdv with normal TreeView and TreeNode.

using Syncfusion.Windows.Forms.Tools;

namespace treeviewtest
{
    public partial class Form1 : Form
    {
        TreeNodeAdv CurrentNode = null;
        public Form1()
        {
            InitializeComponent();
        }

        private void treeViewAdv1_AfterCheck(object sender, Syncfusion.Windows.Forms.Tools.TreeNodeAdvEventArgs e)
        {
            TreeViewAdv tree = sender as TreeViewAdv;
            if (Control.ModifierKeys == Keys.Control 
                  && e.Action!= TreeViewAdvAction.Unknown)
            {

                foreach (TreeNodeAdv node in tree.Nodes)
                {
                    if (node.CheckState == CheckState.Checked && node != CurrentNode)
                        node.Checked = false;

                    foreach (TreeNodeAdv n in node.WalkTree())
                    {
                        if (n.CheckState == CheckState.Checked && n != CurrentNode)
                            n.Checked = false;
                    }
                }
            }
            CurrentNode = null;
        }

        private void treeViewAdv1_BeforeCheck(object sender, TreeNodeAdvBeforeCheckEventArgs e)
        {
            if (Control.ModifierKeys == Keys.Control && CurrentNode == null)
            {
                CurrentNode = e.Node;
                if (e.NewCheckState == CheckState.Unchecked)
                {
                    TreeViewAdv tree = sender as TreeViewAdv;
                    foreach (TreeNodeAdv node in tree.Nodes)
                    {
                        if (node.CheckState == CheckState.Checked && node != CurrentNode)
                            node.Checked = false;

                        foreach (TreeNodeAdv n in node.WalkTree())
                        {
                            if (n.CheckState == CheckState.Checked && n != CurrentNode)
                                n.Checked = false;
                        }   
                    }
                    e.Cancel = true;
                }
            }
        }
    }

    public static class externtree
    {
        public static IEnumerable<TreeNodeAdv> WalkTree(this TreeNodeAdv node)
        {
            if (node == null)
                yield break;

            // return itself first
            yield return node;

            // return children
            if (node.HasChildren)
            {
                foreach (TreeNodeAdv cNode in node.Nodes)
                    foreach (TreeNodeAdv iNode in cNode.WalkTree())
                        yield return iNode;
            }
        }
    }
}

Answer 1

Make it elegant with inheritance and recursion:

using System;
using System.Windows.Forms;

class MyTreeView : TreeView {
    protected override void OnAfterCheck(TreeViewEventArgs e) {
        if (checking) return;
        checking = true;
        if (e.Node.Checked && (Control.ModifierKeys & Keys.Control) == Keys.Control) {
            uncheckNodes(this.Nodes, e.Node);
        }
        checking = false;
        base.OnAfterCheck(e);
    }

    private void uncheckNodes(TreeNodeCollection nodes, TreeNode except) {
        foreach (TreeNode node in nodes) {
            if (node != except) node.Checked = false;
            uncheckNodes(node.Nodes, except);
        }
    }
    private bool checking;
}