Question

I am making a simple web part which queries an SQL database to pull a list of people into a drop down list. When a user of that drop down list is selected, it populates a datagrid with additional information about that user via another sql query.

I have the SQL Server and SQL Database as custom properties.

My problem is that when the custom properties are changed and ‘Ok’ is hit, the databound control does not populate. Instead, I have to then refresh the page again for my data to bind.

I know this is an issue with web part life cycle so was hoping you guys could assist me.

I did try putting my databinding code into the OnPreRender as suggested here, but I then found that when the user was changed in the drop down box, it would re-bind all the data and automatically set the user back at the first in the list.

My entire code:

using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using System.Data;
using System.Data.SqlClient;
using Microsoft.SharePoint.WebPartPages;
using WebPart = System.Web.UI.WebControls.WebParts.WebPart;


namespace SampleProject.SampleWebPart
{
    [ToolboxItemAttribute(false)]
    public class SampleWebPart : WebPart
    {
        public DropDownList dl = null;
        public DataGrid dg = null;
        private string _SqlServer;
        private string _SqlDb;

        [Personalizable(PersonalizationScope.Shared),
         WebBrowsable(true),
         WebDisplayName("SQL Server"),
         WebDescription("Specify the SQL Server to connect to. eg. VM188"),
         SPWebCategoryName("Data Connection Properties"),
         DefaultValue(".")]
        public string SqlServer
        {
            get { return _SqlServer; }
            set { _SqlServer = value; }
        }

        [Personalizable(PersonalizationScope.Shared),
        WebBrowsable(true),
        WebDisplayName("Database Name"),
        WebDescription("Specify the Database to connect to. eg. Test"),
        SPWebCategoryName("Data Connection Properties"),
        DefaultValue("Test")]
        public string SqlDb
        {
            get { return _SqlDb; }
            set { _SqlDb = value; }
        }

        protected override void CreateChildControls()
        {
            if (string.IsNullOrEmpty(this.SqlServer) || string.IsNullOrEmpty(this.SqlDb))
            {
                //If just added, ask to configure in toolpane first.
                LiteralControl literalCtrl = new LiteralControl(
                string.Format("<a id='MsoFrameworkToolpartDefmsg_{0}' href=\"javascript:ShowToolPane2Wrapper('Edit','129','{0}');\">Open the tool pane and enter a valid value.", this.ID));
                this.Controls.Add(literalCtrl);
            }
            else
            {
                try
                {


                    System.Web.UI.UpdatePanel detailsUpdatePanel = new System.Web.UI.UpdatePanel();
                    detailsUpdatePanel.ID = "DetailsUpdatePanel";
                    detailsUpdatePanel.UpdateMode = UpdatePanelUpdateMode.Conditional;
                    this.Controls.Add(detailsUpdatePanel);

                    dl = new DropDownList();
                    dg = new DataGrid();

                    dl.AutoPostBack = true;
                    dl.SelectedIndexChanged += new EventHandler(dl_SelectedIndexChanged);

                    dl.ID = "selectPersonDl";
                    dg.ID = "personDetailsDg";
                    detailsUpdatePanel.ContentTemplateContainer.Controls.Add(dl);
                    detailsUpdatePanel.ContentTemplateContainer.Controls.Add(dg);

                    if (!Page.IsPostBack)
                    {
                        //Populate the drop down list
                        dl.DataSource = GetNames();
                        dl.DataValueField = "Person";
                        dl.DataTextField = "Person";
                        dl.DataBind();

                        //Populate the data grid
                        dg.DataSource = GetData(dl.SelectedValue);
                        dg.DataBind();
                    }

                }
                catch (Exception ex)
                {
                    Label lblError = new Label();
                    lblError.Text = ex.Message;
                    this.Controls.Add(lblError);
                }

                Label lblServ = new Label();
                lblServ.Text = this.SqlServer;
                this.Controls.Add(lblServ);
                Label lblDb = new Label();
                lblDb.Text = this.SqlDb;
                this.Controls.Add(lblDb);



                base.CreateChildControls();
            }
        }


        protected void dl_SelectedIndexChanged(object sender, EventArgs e)
        {
            //
            dg.DataSource = GetData(dl.SelectedValue);
            dg.DataBind();
        }

        protected SqlDataReader GetNames()
        {
            SqlConnection cn = new SqlConnection("server=" + this.SqlServer + "; database=" + this.SqlDb + ";integrated security=true");
            SqlCommand cmd = new SqlCommand("Select Person from Sample", cn);
            cn.Open();
            return cmd.ExecuteReader();
        }

        protected SqlDataReader GetData(string person)
        {
            SqlConnection cn = new SqlConnection("server=" + this.SqlServer + "; database=" + this.SqlDb + ";integrated security=true");
            SqlCommand cmd = new SqlCommand("Select DateMod, Sample FROM Sample WHERE Person='" + person + "'", cn);
            cn.Open();
            return cmd.ExecuteReader();

        }

    }
}

NOTE: I did some more thinking – could be it because I have the binding wrapped inside a !IsPostBack if statement? I’m not sure…

Answer 1

You have to trigger the databinding either on Page_Load or Page_PreRender.
You’re right when you say the users selection gets dropped if you just databind it in either these 2 methods.
The trick to avoid this is to only databind if the page loaded without a postback.
Your page_prerender or page_load would have to look like this :

if(!IsPostBack)
{
  dg.DataSource = GetData();
  dg.DataBind();
}