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DropDownList retnring error OnSelectedIndexChanged

dodgerfan asked
Last Modified: 2012-06-27
I have an ASP.Net page for user input. I have 2 drop down lists. Once a selection is made from the first list, the values for the second list need to be populated based on that first selection. I am getting an error when you make the selection from the first list. It is an Object reference not set to an instance of an object. It appears that the second recordset that needs to be populated is empty. I have put in a reponse.write to ensure that there is a value selected, and it always displays the id selected. So I'm not sure where my code is going wrong. Any help is appreciated. My code:

protected void Page_Load(object sender, EventArgs e)
        if (!IsPostBack) BindLocations();

    protected void ddlLocation_SelectedIndexChanged(object sender, EventArgs e)
        DropDownList ddlLocation  = (DropDownList)PersonData.FindControl("ddlLocation ");
        DropDownList ddlOfficers = (DropDownList)PersonData.FindControl("ddlOfficers");

        using (SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["myConn"].ToString()))
            ddlOfficers.DataTextField = "Last_Name";
            ddlOfficers.DataValueField = "UserID";
            SqlCommand cmd = new SqlCommand("SELECT UserID, LocationID, Last_Name FROM vw_Officers WHERE Location_ID = @LocationID", conn);
            cmd.Parameters.Add(new SqlParameter("@LocationID", ddlLocation.SelectedValue));
            ddlOfficers.DataSource = cmd.ExecuteReader(CommandBehavior.CloseConnection);
        ddlOfficers.Enabled = true;

    protected void BindLocations()
        DropDownList ddlLocation = (DropDownList)PersonData.FindControl("ddlLocation");
        using (SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["myConn"].ToString()))
            ddlLocation .DataTextField = "Name";
            ddlLocation .DataValueField = "LocationID";
            SqlCommand cmd = new SqlCommand("SELECT LocationID, Name, UserID FROM vw_Locations WHERE UserID = @UserID", conn);
            cmd.Parameters.Add(new SqlParameter("@UserID", SqlDbType.Int).Value = SessionHelper.GetUserId();
            ddlLocation .DataSource = cmd.ExecuteReader(CommandBehavior.CloseConnection);
            ddlLocation .DataBind();
        ddlLocation .Items.Insert(0, new ListItem("SELECT A LOCATION", "-1"));
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