C#

public Form1()
{
    InitializeComponent();
    this.treeView1.BeforeExpand += new TreeViewCancelEventHandler(treeView1_comb);
    this.treeView1.BeforeCheck += new TreeViewCancelEventHandler(treeView1_comb);
    this.treeView1.Click += new EventHandler(treeView1_comb);
    this.treeView1.BeforeCollapse += new TreeViewCancelEventHandler(treeView1_comb);

}


void treeView1_comb(object sender, EventArgs e)
{
    if (e is TreeViewCancelEventArgs)
    {
        TreeViewCancelEventArgs te = e as TreeViewCancelEventArgs;

        if (te.Action == TreeViewAction.Expand)
        {
            /*node expanded*/
            MessageBox.Show("On Expand");
        }
        else if (te.Action == TreeViewAction.Collapse)
        {
            /*node Collapsed*/
            MessageBox.Show("On Collapse");
        }
        else if (te.Action == TreeViewAction.ByKeyboard || te.Action == TreeViewAction.ByMouse)
        {
            /*node checked*/
            MessageBox.Show("On Check");
        }

    }
    else
    {
        //the node is just clicked
        MessageBox.Show("On Click");
    }
}