saving data in datatable using recursive function

Question

In the below function I have a DataTable which resets during recursion of the function. How can I solve this problem? I have to create table once and add rows repeatedly in each repeat of the function. Please help! private DataTable GetSelectedTreeNodes(TreeNode parentTreeNode) { DataTable tvp = new DataTable(); tvp.Columns.Add(new DataColumn(Suburb)); if (parentTreeNode.Checked) { ListBox1.Items.Add(parentTreeNode.Text); tvp.Rows.Add(parentTreeNode.Text); tvp.Rows.Add(parentTreeNode.Text); } if (parentTreeNode.ChildNodes.Count > 0) { foreach (TreeNode childTreeNode in parentTreeNode.ChildNodes) { GetSelectedTreeNodes(childTreeNode); } } return tvp; }

Prakash Malakar · Answer

Server Error in '/' Application. Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Line 295: tvp.Rows.Add(parentTreeNode.Text); Line 296: tvp.Rows.Add(parentTreeNode.Text); Line 297:

Syed Shanu · Answer

You can Declare the Datatable as Global variable for example. If is this is Web application then DataTable tvp; publiv void Page_Load { if(!page.ispostback) { tvp = new DataTable(); tvp.Columns.Add(new DataColumn(Suburb)); } } //here your method private DataTable GetSelectedTreeNodes(TreeNode parentTreeNode) { if (parentTreeNode.Checked) { ListBox1.Items.Add(parentTreeNode.Text); tvp.Rows.Add(parentTreeNode.Text); tvp.Rows.Add(parentTreeNode.Text); } if (parentTreeNode.ChildNodes.Count > 0) { foreach (TreeNode childTreeNode in parentTreeNode.ChildNodes) { GetSelectedTreeNodes(childTreeNode); } } return tvp; }