display div if dropdownlist value is selected with C#

问题

I'm trying to make a Div appear if special "option" is selected in a Drop Down list. No matter what I try I can't make it work. I tried other pages here but nothing seems to make it work.

My C# code

protected void ddlSubject_SelectedIndexChanged(object sender, EventArgs e)
{
    if (ddlEmne.SelectedValue == "Lej os")
    {
        divselected.Visible = true;
    }
    if (ddlEmne.SelectedValue == "")
    {
        divselected.Visible = false;
    }
}

My DropDownList:

<asp:DropDownList CssClass="margtop" ID="ddlEmne"  runat="server" OnSelectedIndexChanged="ddlSubject_SelectedIndexChanged">
                <asp:ListItem Value="Pakke Løsninger">Pakke Løsninger</asp:ListItem>
                <asp:ListItem Value="Spørgsmål">Spørgsmål</asp:ListItem>
                <asp:ListItem Value="Lej os">Lej os</asp:ListItem>
                <asp:ListItem Value="Andet">Andet</asp:ListItem>
            </asp:DropDownList>

and the div I want to show/hide :

<div id="divselected" runat="server" style="visibility: hidden;">
    s
</div>

Hope that someone can say that I'm doing wrong.

回答1:

You need to Enable the AutoPostBack of the dropdownlist for raising the OnSelectedIndexChanged event on server side.

asp:DropDownList CssClass="margtop" ID="ddlEmne" AutoPostBack="true" runat="server" OnSelectedIndexChanged="ddlSubject_SelectedIndexChanged">

and change the markup: visible is the attribute of html elements, so you can directly use it like this.

 <div id="divselected" runat="server" visible="false">
    s
 </div>

来源：https://stackoverflow.com/questions/21068367/display-div-if-dropdownlist-value-is-selected-with-c-sharp

标签

ASP.NET

html-select