[RESOLVED] Binding data from table to Treeview in ASP.NET C#

Hi friends, I am trying to bind table values to treeview control in asp.net c#. I want the output of treeview as following:

 

Control1

       Sub-Control1

       Sub-Control2

       Sub-Control3

Control2

       Sub-Control1

       Sub-Control2

       Sub-Control3

Control3

       Sub-Control1

       Sub-Control2

       Sub-Control3

Control4

       Sub-Control1

       Sub-Control2

       Sub-Control3

 

But I’m getting “Object Reference not set to an instance of object” Error. Please help me. I have posted my code below.

 

Thanks.

 

SqlCommand cmd_Select_Parent_Nodes = new SqlCommand("Select DISTINCT control_Type from tbl_Controls", con);

                SqlDataAdapter da_Parent = new SqlDataAdapter(cmd_Select_Parent_Nodes);

                ds_Parent = new DataSet();

                da_Parent.Fill(ds_Parent);

 

 

                int parentNodes = ds_Parent.Tables[0].Rows.Count;

 

                TreeNode[] HeaderNode = new TreeNode[parentNodes];

 

                for (int i = 0; i < parentNodes; i++)

                {

 

                    string header = ds_Parent.Tables[0].Rows[i]["control_Type"].ToString();

 

                    HeaderNode[i].Text = header;

 

 

                    SqlCommand cmd_Select_Child_Nodes = new SqlCommand("Select control_Name from tbl_Controls where control_Type = @Type", con);

                    cmd_Select_Child_Nodes.Parameters.AddWithValue("@Type", HeaderNode[i].Text);

                    DataSet ds_Child = new DataSet();

                    SqlDataAdapter da_Child = new SqlDataAdapter(cmd_Select_Child_Nodes);

                    da_Child.Fill(ds_Child);

                   

                    int childNodes = ds_Child.Tables[0].Rows.Count;

 

                    TreeNode[] RootNodes = new TreeNode[childNodes];

 

                    for (int node = 0; node < childNodes; node++)

                    {

                        RootNodes[node].Text = ds_Child.Tables[0].Rows[node]["control_Name"].ToString();

                        HeaderNode[i].ChildNodes.Add(RootNodes[node]);

                    }

controls_TreeView.Nodes.Add(HeaderNode[i]);

}

You can do in following way:

http://techbrij.com/display-hierarchical-data-with-treeview-in-asp-net

refer following thread:

http://forums.asp.net/t/1685783.aspx/1?I+want+to+bind+data+to+treeView+control+

hi,

avoid use  TreeNode[] it is too easy to make mistake .  childnode is relation with parentNode .we can use a loop that contains the loop to load child nodes .

such as :

foreach (DataRow c in dtTree)
            {
                TreeNode ParentNode = new TreeNode();
                ParentNode.Text = c.StudentID;
                ParentNode.Value = c.StudentID;
                TreeView1.Nodes.Add(ParentNode);
                List list2 = dal.FindAll();
                foreach (DataRow d in dtTree.Select("control_Type  = " + c.id))
                {
                    TreeNode ChildNode = new TreeNode();
                    ChildNode.Text = d.StudentID;
                    ChildNode.Value = d.StudentID;
                    ParentNode.ChildNodes.Add(ChildNode);
                }
            }

Hope this helps

 

 

 

to find the actual reason of this error, please have a detailed look on the exception object and specially the stack-strace. to me, following lines of code can be
problematic if do not check them for null/empty values, as it is not necessary the every parent must has childs in database.

// if "control_Type" allows null it will fail
string header = ds_Parent.Tables[0].Rows[i]["control_Type"].ToString();

// if parent has zero childs then it may crash
int childNodes = ds_Child.Tables[0].Rows.Count;

i hope you got my point, thanks