在页面加载时强制下拉列表SelectMethod

Question

I'm developing a little web-form based web application. It uses some DropDownList asp controls. This is the control which I've appended a default empty value --- seleziona ---

                <asp:DropDownList
                    ID="dropQuestionari"
                    runat="server"
                    SelectMethod="GetQuestionari"
                    AppendDataBoundItems="true"
                    ItemType="Models.Questionario"
                    DataTextField="Questionariointestazione"
                    DataValueField="idQuestionario">
                    <asp:ListItem Text="--- seleziona ---" Value="" Selected="true"></asp:ListItem>
                </asp:DropDownList>

The control uses SelectMethod property with GetQuestionari() method that retrieves all the items needed to populate the list.

It work fine, but I need to check if the drop-down list is empty (excluding the default item) and change the default object text if so. I tried like this (in code behind):

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        //...

        if (dropQuestionari.Items.Count == 1) 
        {
            dropQuestionari.Items[0].Text = "Nessun questionario per l'utente corrente";
            this.confirmButton.Enabled = false;
        }
    }
}

It seems that the list is not populated at page-load and dropQuestionari.Items.Count always returns 1 (obviously it counts only the default item). How can I force the list to be populated in the PageLoad?

Answer 1

You're checking the count when the page ISN'T a post back, meaning it's the first time the page is loaded. If it's the first time, the DDL would not be populated.