Question

I’m trying to create some cascading drop downs. I have my States loading via C# page load fine. I just can’t seem to get anything to fire off to load the cities. After the cities, I’ll be adding another drop down, but I can figure that out once I have this working.

I did notice “Default.aspx/LoadCitiesByState 500 (Internal Server Error)” in my Chrome errors.

C#

    protected void LoadStates()
{
    // Populate State dropdown box
    ListItem li = new ListItem();
    li.Value = "0";
    li.Text = "Select One";

    DataSet dsState = SharedData.GetStates();
    ddlState.DataSource = dsState.Tables[0].DefaultView;
    ddlState.DataValueField = "ab";
    ddlState.DataTextField = "name";
    ddlState.DataBind();
    ddlState.Items.Insert(0, li);
}


[WebMethod]
protected void LoadCitiesByState(string state)
{
    ListItem li = new ListItem();
    li.Value = "0";
    li.Text = "Select One";

    DataTable dt = new DataTable();
    dt = SharedData.GetCities(state);
    ddlCity.DataSource = dt.Rows[0].Table.DefaultView;
    ddlCity.DataValueField = "ListCity";
    ddlCity.DataTextField = "ListCity";
    ddlCity.DataBind();
    ddlCity.Items.Insert(0, li);
}

Markup

<asp:DropDownList ID="state" runat="server" MaxLength="50" Style="width: 200px;" />

<asp:DropDownList ID="city" runat="server" MaxLength="50" Style="width: 200px;" /> 



function loadCities(selectedItem) {
            $.ajax({
                type: "POST",
                url: "Default.aspx/LoadCitiesByState",
                data: "selectedItem",
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                async: true,
                success: function Success(data) {
                    alert(selectedItem);
                }
            });

Answer 1

I see you haven’t set autopostback to true in asp:DropDownList.