Question

I am trying to assign a ViewState value in my application with a SelectedIndexChanged function. Once it’s assigned the postback will use the value to change some data and then set the value to zero but I can’t seem to get it to work correctly. The controls are all created dynamically on Page_Load.

Page Load

protected void Page_Load(object sender, EventArgs e)
{
    CreateAttributeControls();
    TempProductVariantId = 0;
}

Create Attribute Controls

public void CreateAttributeControls()
{
    ...
    var ddlArtistArtworks = new DropDownList();
    ddlArtistArtworks.ID = "ddlArtistArtworksTest";
    divAttribute.Controls.Add(ddlArtistArtworks);
    ddlArtistArtworks.Items.Clear();
    ddlArtistArtworks.SelectedIndexChanged += new EventHandler(ArtistArtwork_SelectedIndexChange);
    ddlArtistArtworks.AutoPostBack = true;
    ...
}

ArtistArtwork_SelectedIndexChange

protected void ArtistArtwork_SelectedIndexChange(object sender, EventArgs e)
{
    DropDownList ddl = sender as DropDownList;
    TempProductVariantId = int.Parse(ddl.SelectedValue);
}

TempProductVariantId ViewState Save

public int TempProductVariantId
{
    get
    {
        if (ViewState["TempProductVariantId"] == null)
            return 0;
        else
            return (int)ViewState["TempProductVariantId"];
    }
    set
    {
        ViewState["TempProductVariantId"] = value;
    }
}

When I load the page everything is fine. I change the DropDownList’s value, It posts back, and the value is not set. Change it again the value is set and continues to change as I change the value of the DropDownList.

Any guidance on this would be greatly appreciated.

Note: I have tried changing when CreateAttributeControls() is called. In OnPreRender for example. I was given this to understand the lifecycle of the page Life Cycle

Answer 1

That’s because you are essentially recreating the dropdown on every postback..

try this

public void CreateAttributeControls()
{
    ...
    DropDownList ddlArtistArtworks;
    if (!IsPostBack)
    {
        ddlArtistArtworks = new DropDownList();
        ddlArtistArtworks.ID = "ddlArtistArtworksTest";
        divAttribute.Controls.Add(ddlArtistArtworks);
        ddlArtistArtworks.Items.Clear();
        ddlArtistArtworks.AutoPostBack = true;
    }
    else
    {
         ddlArtistArtworks = (DropDownLise)divAttribute.FindControl("ddlArtistArtworksTest");
    }

    ddlArtistArtworks.SelectedIndexChanged += new EventHandler(ArtistArtwork_SelectedIndexChange);
    ...
}

For dynamically added controls, the event handler has to be linked up everytime so that has to be done outside the if-block, unconditionally.