asp:gridview filter using listbox cannot make multiple selection

Question

I have this asp:gridview in which I show data using mySql stored procedure. I have this listbox named ddlstatus which I use to filter the data. I use viewstate to show data that are selected from the listbox. The problem is I want to make multiple selection on this listbox and show data for each selection made on it, but when it only shows data for the initial selection.

The below is the client side code:

<asp:Label ID="lblstat" Text="status" Visible="false" runat="server"></asp:Label>
<asp:ListBox ID="ddlstatus" runat="server" OnSelectedIndexChanged="DropDownChange" AutoPostBack="true" AppendDataBoundItems="true" SelectionMode="Multiple"></asp:ListBox>

<asp:GridView ID="gdvTM" runat="server" ControlStyle-Width="100%"  AutoGenerateColumns="False" DataKeyNames="ID" OnRowDeleting="gdvTM_RowDeleting" PageSize="5" CssClass="cssgridview" AlternatingRowStyle-BackColor="#d5d8dc">
    <Columns >
       <asp:TemplateField HeaderText="Current Status">
         <ItemTemplate >
             <asp:Label ID="lblcstat" runat="server" Text='<%# Eval("status") %>'></asp:Label>
        </ItemTemplate>
      </asp:TemplateField>
    </Columns>
</asp:GridView>

The below is the server side code:

private void BindDropDownList()
{
    PopulateDropDown(ddlstatus, lblstat.Text);
}
private void PopulateDropDown(ListBox ddl, string columnName)
{
    ddl.Items.Clear();
    ddl.DataSource = BindDropDown(columnName);
    ddl.DataTextField = columnName;
    ddl.DataValueField = columnName;
    ddl.DataBind();
    ddl.Items.Insert(0, new ListItem("Please select", "0"));
}
private void BindGrid()
{
    DataTable dt = new DataTable();
    String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["connStr"].ConnectionString;
    MySqlConnection con = new MySqlConnection(strConnString);
    MySqlDataAdapter sda = new MySqlDataAdapter();
    MySqlCommand cmd = new MySqlCommand("GetTMData");
    cmd.CommandType = CommandType.StoredProcedure;  
    string statusVal = null;
    if (ViewState["stat"] != null && ViewState["stat"].ToString() != "0")
    {
        statusVal = ViewState["stat"].ToString();
    }
    cmd.Parameters.AddWithValue("statusVal", statusVal);
    cmd.Connection = con;
    sda.SelectCommand = cmd;
    sda.Fill(dt);
    gdvTM.DataSource = dt;
    int i = dt.Rows.Count;
    gdvTM.DataBind();
    this.BindDropDownList();
    TableCell cell = gdvTM.HeaderRow.Cells[0];
    setDropdownselectedItem(ViewState["stat"] != null ? (string)ViewState["stat"] : string.Empty, ddlstatus);
}
private void setDropdownselectedItem(string selectedvalue, ListBox ddl)
{
    if (!string.IsNullOrEmpty(selectedvalue))
    {
         ddl.Items.FindByValue(selectedvalue).Selected = true;

    }
}
protected void DropDownChange(object sender, EventArgs e)
 {
      ListBox dropdown = (ListBox)sender;
      string selectedValue = dropdown.SelectedItem.Value;
      switch (dropdown.ID.ToLower())
      {
          case "ddlstatus":
             ViewState["stat"] = selectedValue;
             break;
      }

      this.BindGrid();
 }

private DataTable BindDropDown(string columnName)
{
    string username = uName.Text;
    String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["connStr"].ConnectionString;
    MySqlConnection con = new MySqlConnection(strConnString);
    MySqlCommand cmd = new MySqlCommand("SELECT DISTINCT (" + columnName + ") FROM approved WHERE tm = @tm AND " + columnName + " IS NOT NULL", con);
    MySqlDataAdapter sda = new MySqlDataAdapter(cmd);
    cmd.Parameters.AddWithValue("@tm", username);
    DataTable dt = new DataTable();
    sda.Fill(dt);
    return dt;
}

Below is the MySql stored procedure:

CREATE DEFINER=`root`@`localhost` PROCEDURE `GetTMData`(in statusVal varchar(45))
BEGIN
SELECT *
   FROM approved
   WHERE (statusVal IS NULL
                OR status = statusVal)
         order by date desc;
END

How can I make this happen? Thanks in advance.

Answer 1

Please make listbox multiple

<asp:ListBox id="ListBox1" 
           Rows="6"
           Width="100px"
           **SelectionMode="Multiple"** 
           runat="server">

         <asp:ListItem Selected="True">Item 1</asp:ListItem>
         <asp:ListItem>Item 2</asp:ListItem>
         <asp:ListItem>Item 3</asp:ListItem>
         <asp:ListItem>Item 4</asp:ListItem>
         <asp:ListItem>Item 5</asp:ListItem>
         <asp:ListItem>Item 6</asp:ListItem>

      </asp:ListBox>

Then in server side void SubmitBtn_Click(Object sender, EventArgs e) {

     Message.Text = "You chose: <br />";

     // Iterate through the Items collection of the ListBox and 
     // display the selected items.
     foreach (ListItem item in ListBox1.Items)
     {

        if(item.Selected)
        {

           Message.Text += item.Text + "<br />";

        }

     }

  }