EnableViewState not working in DropDownList

Question

The default.aspx page has a DropDownList which is populated in the code behind only when it is not a postback. When a value is selected a method is called which fills a Literal with the selected value. It works as expected. The problem is when I set the page to not EnableViewState enabling it in the DropDownList control only. In this case when posted back the DropDownList loses its items. I have setup a new Web project just to test this. There is no master page to make it simpler.

Default.aspx:

<%@ Page Title="Home Page" Language="C#" AutoEventWireup="true"
    CodeBehind="Default.aspx.cs" Inherits="WebApplication4._Default" 
    EnableViewState="false" %>

<asp:DropDownList ID="DDL" runat="server" 
    OnSelectedIndexChanged="DDL_OSIC" 
    AutoPostBack="true" 
    EnableViewState="true">
</asp:DropDownList>

<asp:Literal ID="Literal1" runat="server"></asp:Literal>

Default.aspx.cs:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        DDL.Items.Add("red");
        DDL.Items.Add("green");
        DDL.Items.Add("blue");
    }
}
protected void DDL_OSIC(object sender, EventArgs e)
{
    Literal1.Text = DDL.SelectedValue;
}

Why isn't EnableViewState working?

Clodoaldo Neto Clodoaldo Neto · Accepted Answer · 2012-08-02T23:17:47

Found the answer with the help of a deleted answer. The deleted answer was wrong just because it was incomplete. With that hint I found the ViewStateMode Property page.

Summarizing it to disable all controls' ViewState and enable it just for the choosen ones:

Set both the page and all the control's EnableViewState property to true. This is the default so it is not necessary to write anything
Set the page ViewStateMode to Disabled
Set ViewStateMode to Enabled in the control where you want ViewState enabled

EnableViewState not working in DropDownList

2 Answers