WebPart on Top of Displayform for Custom List, ListItem deleted => Server Error

Question

so I have a visual webpart for registering/unregistering for an event on top of a custom lists' ("events"-list) display form (added via &ToolPaneView=2).

Now my use-case is this: potential Attendee opens the display form and wants to register. But he has to [get some coffee first, etc...] first - so he lets the display form openend.

While [attendee gets coffee etc...] an Editor deletes the corresponding Entry of the events-list.

Now later on, the potential attendee comes back and tries to register for the - now deleted - event. And now there's my problem: Instead of showing a) the error message as defined in my catch-block, or b) redirecting as you could see in the code I'll add, I get a server error in appliaction (you know, this yellow page which should never show up ;) ) - in this error page it shows the message, that the object is renamed or deleted by another user - but that's not wanted. I want a) error label showing the text (same as in server error page) or if that's not working because the displayform is not there b) redirect to a defined error page where I'd add the text. So, what am I missing? Would be great to get an answer!

So, this is my relevant code (I hope so, at least, ask for more if you want :) ):

    protected void Page_Load(object sender, EventArgs e)
    {
        try
        {
            ...
            currentEventItem = (SPListItem)SPContext.Current.Item;   
            ...
        }
        catch (Exception ex)
        {
            ErrorLabel.Text = "Fehler: " + ex.Message 
                            + "StackTrace: " +ex.StackTrace;   
        } 
    }

and

    protected void ButtonRegister_Click(object sender, EventArgs e)
    {
        try
        {
            //trying to check if item exists here
            SPList eventslist = website.Lists["eventsListString"];
            if (eventslist.GetItemById(currentEventItem.ID) != null)
            {
                bool full = IsFull(registrations, maxRegistrations);
                ResetLabel();
                if (!full)
                {
                    ...
                }
                else
                {
                    ...
                }
            }
            else
            {
                //tried to redirect the response to an error page
                Response.Redirect("ErrorPageString");
            }
        }
        catch (Exception ex)
        {
            ErrorLabel.Text = "Problem: " + ex.Message
            //...(loggingservice)                
        }
    }

So as I thought, the pot. attendee becomes a) redirected to my error page, or b) the catch-block is reached and I get output to my errorlabel (which is in the webpart in top of displayform... maybe that's the problem?) - but all I get is this huge messy error page.

Hope you could help me for I am out of Ideas.

Best regards, Dominik

Answer 1

Create a base class for your web parts that handles exceptions. That way the page doesn't fail, just your web part. The error message is displayed on the page where your web part should be, the surrounding web parts are rendered normally. I use this as the base class for all my web parts.

http://andreascode.blogspot.com/2007/12/general-exception-handling-in-web-parts.html