Question

I am getting this 500 error:

Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500

UPDATE:

My Error is actually this:
System.Web.UI.ViewStateException

if (viewStates.Length != list.Items.Count + 1)
{
    throw new ViewStateException();
}

I have been getting it ever since I added this adapter to my site that is shown on this tutorial.

ASP.NET DropDownList with OptionGroup support

It loads the DropDownList just fine in all pages but when I do any postbacks, regular or ajax is when the error appears. Here is my exact code for the adapter and the browser file.

Adapter Class

public class DropDownListAdapter : WebControlAdapter
{
    private const string OptionGroupAttribute = "OptionGroup";
    private const string TagOptionGroup = "optgroup";
    private const string AttributeLabel = "label";
    protected override void RenderContents(HtmlTextWriter writer)
    {
        DropDownList list = Control as DropDownList;
        string currentOptionGroup;
        List<string> renderedOptionGroups = new List<string>();
        foreach (ListItem item in list.Items)
        {
            Page.ClientScript.RegisterForEventValidation(
                list.UniqueID, 
                item.Value);
            if (item.Attributes[OptionGroupAttribute] == null)
            {
                RenderListItem(item, writer);
            }
            else
            {
                currentOptionGroup = item.Attributes[OptionGroupAttribute];
                if (renderedOptionGroups.Contains(currentOptionGroup))
                {
                    RenderListItem(item, writer);
                }
                else
                {
                    if (renderedOptionGroups.Count > 0)
                    {
                        RenderOptionGroupEndTag(writer);
                    }
                    RenderOptionGroupBeginTag(currentOptionGroup, writer);
                    renderedOptionGroups.Add(currentOptionGroup);
                    RenderListItem(item, writer);
                }
            }
        }
        if (renderedOptionGroups.Count > 0)
        {
            RenderOptionGroupEndTag(writer);
        }
    }

    private void RenderOptionGroupBeginTag(string name, HtmlTextWriter writer)
    {
        writer.AddAttribute(AttributeLabel, name);
        writer.RenderBeginTag(TagOptionGroup);
    }

    private void RenderOptionGroupEndTag(HtmlTextWriter writer)
    {
        writer.RenderEndTag();
    }

    private void RenderListItem(ListItem item, HtmlTextWriter writer)
    {
        foreach (string key in item.Attributes.Keys)
        {
            if (key != OptionGroupAttribute)
            {
                writer.AddAttribute(key, item.Attributes[key]);
            }
        }
        writer.AddAttribute(HtmlTextWriterAttribute.Value, item.Value, true);
        if (item.Selected)
        {
            writer.AddAttribute(HtmlTextWriterAttribute.Selected, "selected");
        }
        writer.RenderBeginTag(HtmlTextWriterTag.Option);
        writer.WriteEncodedText(item.Text);
        writer.RenderEndTag();
    }

    protected override object SaveAdapterViewState()
    {
        DropDownList list = Control as DropDownList;
        object[] viewStates = new object[list.Items.Count + 2];

        int i = 0;
        foreach (ListItem item in list.Items)
            viewStates[i++] = item.Attributes[OptionGroupAttribute];

        viewStates[i++] = base.SaveAdapterViewState();
        viewStates[i] = Hash(list.Items);

        return viewStates;
    }

    private static int Hash(ListItemCollection listItems)
    {
        int hash = 0;
        foreach (ListItem listItem in listItems)
            hash += listItem.GetHashCode();

        return hash;
    }

    object[] viewStates;

    protected override void LoadAdapterViewState(object state)
    {
        viewStates = (object[])state;
        base.LoadAdapterViewState(viewStates[viewStates.Length - 1]);
    }

    protected override void OnPreRender(System.EventArgs e)
    {
        if (viewStates != null && viewStates.Length > 1)
        {
            DropDownList list = Control as DropDownList;
            if (Page.EnableEventValidation)
            {
                if (viewStates.Length != list.Items.Count + 1)
                {
                    throw new ViewStateException();
                }
            }
            if (Hash(list.Items) == (int)viewStates[viewStates.Length - 1])
            {
                int max = viewStates.Length - 2;
                if (list.Items.Count < max)
                {
                    max = list.Items.Count;
                }
                for (int i = 0; i < max; i++)
                {
                    list.Items[i].Attributes[OptionGroupAttribute] = 
                        (string)viewStates[i];
                }
            }
        }
        base.OnPreRender(e);
    }
}

Browser File:

<browsers>
  <browser refID="default">
    <controlAdapters>
      <adapter
          controlType="System.Web.UI.WebControls.DropDownList"
          adapterType="DropDownListAdapter" />
    </controlAdapters>
  </browser>
</browsers>

StackTrace

NopSolutions.NopCommerce.Web.DropDownListAdapter.OnPreRender(EventArgs e) in ...
   // I'm guessing the issue is here
   System.Web.UI.Control.PreRenderRecursiveInternal() +8948774
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2496

If anyone can point me in the right direction on how to fix this that would be awesome. Now please don’t tell me to disable validateRequest because that doesn’t solve the problem it just covers it up.

Answer 1

You probably already solved this problem or just followed another path, but for future reference.

In SaveAdapterViewState you save state to an object array with a length of x + 2:

object[] viewStates = new object[list.Items.Count + 2];

Then, in LoadAdapterViewState you initialize a local field viewStates with the object array coming from view state:

viewStates = (object[])state;

Finally, in OnPreRender you’re ensuring that the local field viewStates has a length of x + 1 which will fail because you saved an array of length x + 2 and that’s what you’ll get when you load it from view state.