Question

I have a TreeView control in my ASP.NET web application, and I have problems with the event selected node changed, I click on some node in the treeview but the event doesn’t trigger, I have some instructions there that are not executed, I checked with debugger also.

<asp:TreeView ID="ArboreSarcini" runat="server" ImageSet="News" 
onselectednodechanged="ArboreSarcini_SelectedNodeChanged" NodeIndent="10" 
style="z-index: 1; left: 1px; top: 27px; position: absolute; height: 308px; width: 446px">
<HoverNodeStyle Font-Underline="True" BackColor="#99CCCC" Font-Size="12pt" />
<LeafNodeStyle ImageUrl="~/Poze/leaf.png" NodeSpacing="2px" />
<LevelStyles>
<asp:TreeNodeStyle BorderColor="Black" BorderStyle="Solid" BorderWidth="1px" 
Font-Names="Leelawadee" Font-Size="Medium" Font-Underline="False" 
ImageUrl="~/Poze/Root.png" />
<asp:TreeNodeStyle BorderColor="#003300" BorderStyle="Solid" BorderWidth="1px" 
Font-Names="Leelawadee" Font-Underline="False" ImageUrl="~/Poze/node.png" 
Width="400px" />
<asp:TreeNodeStyle BorderColor="#006600" BorderStyle="Solid" BorderWidth="1px" 
Font-Names="Leelawadee" Font-Underline="False" Height="10px" 
ImageUrl="~/Poze/leaf.png" Width="390px" />
</LevelStyles>
<NodeStyle Font-Names="Leelawadee" Font-Size="10pt" ForeColor="Black" 
HorizontalPadding="5px" NodeSpacing="2px" VerticalPadding="0px" 
ImageUrl="~/Poze/node.png" Width="0px" />
<ParentNodeStyle Font-Bold="False" Width="500px" />
<RootNodeStyle ImageUrl="~/Poze/Root.png" />
<SelectedNodeStyle Font-Underline="False" BackColor="#009148" BorderWidth="2px" 
Font-Bold="False" Font-Italic="True" Font-Size="12pt" />
</asp:TreeView>

protected void Button1_Click(object sender, EventArgs e)
{
ArboreSarcini.Nodes.Clear();
populeaza_sarcini();

string sqlstring1 = "Select * from activitati";
System.Data.SqlClient.SqlConnection con1 = new System.Data.SqlClient.SqlConnection(
            "Data Source=BOGDAN-PC\\BOGDAN;Initial Catalog=ePlanning;Integrated Security=SSPI;Connect Timeout=10;TrustServerCertificate=True ");
System.Data.SqlClient.SqlCommand comm1 = new System.Data.SqlClient.SqlCommand(sqlstring1, con1);
System.Data.SqlClient.SqlDataReader reader1;
con1.Open();
reader1 = comm1.ExecuteReader();

while (reader1.Read())
{
foreach (Sarcina s in listaSarcini)
{
    if ((int)reader1["id_sarcina"] == s.Id_sarcina)
    {
        s.ListaActivitati.Add(new Activitate(Convert.ToInt32(reader1["id_activitate"]), reader1["descriere"].ToString()));
    }
}
}

TreeNode tatal = new TreeNode();
tatal.Value = DropListProiecte.SelectedItem.ToString();
//    ArboreSarcini.Nodes.Add(tatal);


TreeNode parentNode = new TreeNode();
foreach (Sarcina sarc in listaSarcini)
{
parentNode = new TreeNode( sarc.Id_sarcina.ToString() + ". " + sarc.Descriere.ToString());


foreach (Activitate act in sarc.ListaActivitati)
{
    TreeNode copil = new TreeNode(act.Id_activitate.ToString()+". "+act.Descriere.ToString() );
    parentNode.ChildNodes.Add(copil);
}
tatal.ChildNodes.Add(parentNode);
//parentNode.Collapse();


}
ArboreSarcini.Nodes.Add(tatal);
con.Close();
ArboreSarcini.ExpandAll();
}


    protected void ArboreSarcini_SelectedNodeChanged(object sender, EventArgs e)
{

    if (ArboreSarcini.SelectedNode.ImageUrl == "~/Poze/node.png")
    {

        System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(
                      "Data Source=BOGDAN-PC\\BOGDAN;Initial Catalog=ePlanning;Integrated Security=SSPI;Connect Timeout=10;TrustServerCertificate=True ");
        //  string de_splituit = ArboreSarcini.SelectedNode.Text;
        string[] id_sarcina = ArboreSarcini.SelectedNode.Text.Split('.');


        string sqlstring = "Select * from sarcini where id_sarcina=" + id_sarcina[0] + ";";




        System.Data.SqlClient.SqlCommand comm = new System.Data.SqlClient.SqlCommand(sqlstring, con);
        System.Data.SqlClient.SqlDataReader reader;

        con.Open();
        reader = comm.ExecuteReader();
        while (reader.Read())
        {
            tbIDSarcina.Text = reader["id_sarcina"].ToString();
        }
    }
}

Answer 1

By default, the TreeView control handles expand-collapse functionality
on the client unless the browser does not support client script or the
EnableClientScript property is set to false. If the
PopulateNodesFromClient property is set to true and the browser
supports client script, then the TreeView control retrieves the data
from the server without posting the entire page back.

When the TreeView control is in selection mode, each time a user
clicks a node, a postback to the server occurs and the
SelectedNodeChanged event is raised.

Typically, you should handle postback events when the TreeView control
is in selection mode or the nodes are being dynamically populated.
This is because either the PopulateOnDemand or PopulateNodesFromClient
property is set to true.

So kindly verify that you set all the required properties. Sharing your HTML might helpful.
Read more about the asp.net treeview here
TreeNode.Nodes Property.
Gets the collection of TreeNode objects assigned to the current tree node.

http://msdn.microsoft.com/en-us/library/system.windows.forms.treenode.nodes.aspx