Call back function for asp:dropdown

Question

User1132714760 posted

Hi 

I have 3 asp:drop down lists. DropDown2 values on DropDown1 selected Item.

Dropdown3 values depend on dropdown2 selected item. I implemented the functionality using onchangeindex functionality. But it is doing pagerefresh on each dropdown item selected.

I want to implement call back for this funtionalty to aviod page refresh.

can some one share the code.

Answer 1

User839733648 posted

Hi TejasviRebba,

According to your description, I suggest that you could use Updatepanel Control to achieve your requirement.

Updatepanel enables sections of a page to be partially rendered without a postback.

I've made a sample and maybe you could refer to.

.aspx

    <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                <table>
                    <tr>
                        <td>Country:</td>
                        <td>
                            <asp:DropDownList ID="ddlCountries" runat="server" AutoPostBack="true" OnSelectedIndexChanged="Country_Changed">
                            </asp:DropDownList>
                        </td>
                    </tr>
                    <tr>
                        <td>State:</td>
                        <td>
                            <asp:DropDownList ID="ddlStates" runat="server" AutoPostBack="true" OnSelectedIndexChanged="State_Changed">
                            </asp:DropDownList>
                        </td>
                    </tr>
                    <tr>
                        <td>City:</td>
                        <td>
                            <asp:DropDownList ID="ddlCities" runat="server">
                            </asp:DropDownList>
                        </td>
                    </tr>
                </table>
            </ContentTemplate>
        </asp:UpdatePanel>
    </form>

code-behind.

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                string query = "select CountryId, CountryName from D_Countries";
                BindDropDownList(ddlCountries, query, "CountryName", "CountryId", "Select Country");
                ddlStates.Enabled = false;
                ddlCities.Enabled = false;
                ddlStates.Items.Insert(0, new ListItem("Select State", "0"));
                ddlCities.Items.Insert(0, new ListItem("Select City", "0"));
            }
        }

        private void BindDropDownList(DropDownList ddl, string query, string text, string value, string defaultText)
        {
            string conString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
            SqlCommand cmd = new SqlCommand(query);
            using (SqlConnection con = new SqlConnection(conString))
            {
                using (SqlDataAdapter sda = new SqlDataAdapter())
                {
                    cmd.Connection = con;
                    con.Open();
                    ddl.DataSource = cmd.ExecuteReader();
                    ddl.DataTextField = text;
                    ddl.DataValueField = value;
                    ddl.DataBind();
                    con.Close();
                }
            }
            ddl.Items.Insert(0, new ListItem(defaultText, "0"));
        }

        protected void Country_Changed(object sender, EventArgs e)
        {
            ddlStates.Enabled = false;
            ddlCities.Enabled = false;
            ddlStates.Items.Clear();
            ddlCities.Items.Clear();
            ddlStates.Items.Insert(0, new ListItem("Select State", "0"));
            ddlCities.Items.Insert(0, new ListItem("Select City", "0"));
            int countryId = int.Parse(ddlCountries.SelectedItem.Value);
            if (countryId > 0)
            {
                string query = string.Format("select StateId, StateName from D_States where CountryId = {0}", countryId);
                BindDropDownList(ddlStates, query, "StateName", "StateId", "Select State");
                ddlStates.Enabled = true;
            }
        }

        protected void State_Changed(object sender, EventArgs e)
        {
            ddlCities.Enabled = false;
            ddlCities.Items.Clear();
            ddlCities.Items.Insert(0, new ListItem("Select City", "0"));
            int stateId = int.Parse(ddlStates.SelectedItem.Value);
            if (stateId > 0)
            {
                string query = string.Format("select CityId, CityName from D_Cities where StateId = {0}", stateId);
                BindDropDownList(ddlCities, query, "CityName", "CityId", "Select City");
                ddlCities.Enabled = true;
            }
        }

result:

Best Regards,

Jenifer

Answer 2

User1132714760 posted

I cannot use asp:ScriptManager as I am integrating my page in another master page and it is already having asp:ScriptManager.

So i cannot use on my page again. So planning  for call back function.

Answer 3

User839733648 posted

Hi TejasviRebba,

I also try the code in a Master page. I just delete the asp:ScriptManager, and it also worls well like below.

If possible, please provide your detailed code and this will be easier to help with you.

Best Regards,

Jenifer