How can i fill a DropDown list using ajax and a c# method

Question

Hi my c# method is this:

[WebMethod] 
    protected static void fillList(HiddenField hiddenControl, System.Web.UI.WebControls.DropDownList listinc)
    {
        int dato = 0;
        string strSql;
        dato = Convert.ToInt32(hiddenControl.Value);

        SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["default"].ToString());
        conn.Open();
        strSql = "SELECT DISTINCT incid FROM HisReportes WHERE peri = " + dato;
        SqlCommand camAND = new SqlCommand(strSql, conn);
        System.Data.DataTable tablainc = new System.Data.DataTable();
        camAND.CommandTimeout = 36000;
        tablainc.Load(camAND.ExecuteReader());

        foreach (DataRow dtrw in tablainc.Rows)
        {            
           listinc.Items.Add(dtrw[0].ToString());
        }

    }

i tested with a onlick function and it works but i need to call it from Ajax function:

$.ajax({
        type: "POST",
        url: "Incio.aspx/fillList",
        data: '{hiddenControl , listinc, dtrw }',
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function(data)
            {
                $.each(data, function (){
                    $("listinc").append($("<option     />").val(this.incidente).text(this.dtrw[0]));
                });
            },
            failure: function () {
                alert("Failed!");
            }
        });

that's my ajax function but it is not filling the dropdown list.

A lot of weird thigs are going on with this code. First fillList method takes 2 parameters but your ajax sends just one parameter and its not even match. Second your code open to SQL injections. I think you need to know how Client/Server side communicate. You can check How to fill a DropDown using Jquery Ajax Call? — Selim Yildiz
– Selim Yildiz, Commented Nov 21, 2019 at 20:06

Angel Cantu · Accepted Answer · 2019-11-21 21:36:24Z

4

you need to return the list from your WebMethod, I recommended you to return a string array from the WebMethod.

    [WebMethod]
    public static string[] fillList()
    {
        your code here....
        return listinc.ToArray();
    }

So, into Ajax in the success function

    $.ajax({
      type: "POST",
      url: "./Inicio.aspx/fillList",
      ...
      success: function (data) {
          let data = data["d"];
          let dropdown = $("#listinc");

          for (let i = 0; i < data.length; i++) {
            // put here your data
            dropdown.append(`<option>${ data[i] }</option>`);
          }
       }
    });

answered Nov 21, 2019 at 21:36

Angel Cantu

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2 Comments

Chris Over a year ago

You are going to have to pass in that Hidden Field value in your web method so he can use in the SQL statement

Angel Cantu Over a year ago

Sure, this is only an example.

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