Yet Another DropDownList.SelectedIndexChanged Dufus

[revbart]

Yep, that's me. I'll bet I've read a hundred articles somewhere or another, but I just can't get the thing to work.

I'm working on a custom solution. One of the major UIs includes a calendar-style presentation. The navigation controls at the top of the calendar include four LinkButton controls (prevYear, prevMonth, nextMonth, nextYear) and two DropDownList controls (monthSelector, yearSelector). The DropDownList webcontrols are set with AutoPostBack=true. I have attached handlers to their SelectedIndexChanged events.

All of the LinkButtons work perfectly. The DropDownLists successfully AutoPostBack. But I can't get my SelectedIndexChanged handler to execute to save my life. Nagging me back in the recesses of my brain is the suspicion that I have solved this one before, but I still just cannot seem to get this to work.

Here's the Control Tree from the Trace, so you can see that these DDLs are buried pretty deep. The object "myCal" of type "Preaching.Web.UI.PreachingCalendar" is my custom control written entirely in C# and packaged up in a DLL.

__Page    ASP.pcal_test_aspx
    ctl05    System.Web.UI.LiteralControl
    ctl00    System.Web.UI.HtmlControls.HtmlHead
        ctl02    System.Web.UI.HtmlControls.HtmlMeta
        ctl03    System.Web.UI.HtmlControls.HtmlMeta
        ctl04    System.Web.UI.HtmlControls.HtmlMeta
        pageTitle    System.Web.UI.HtmlControls.HtmlTitle
    ctl06    System.Web.UI.LiteralControl
    ctl01    System.Web.UI.HtmlControls.HtmlForm
        ctl07    System.Web.UI.LiteralControl
        datasource    Preaching.Web.UI.PreachingEventSqlPager
        ctl08    System.Web.UI.LiteralControl
        myCal    Preaching.Web.UI.PreachingCalendar
            myCal$ctl00    System.Web.UI.WebControls.Table
                myCal$ctl56    System.Web.UI.WebControls.TableRow
                    myCal$ctl57    System.Web.UI.WebControls.TableCell
                        myCal$prevYear    System.Web.UI.WebControls.LinkButton
                        myCal$ctl58    System.Web.UI.LiteralControl
                        myCal$prevMonth    System.Web.UI.WebControls.LinkButton
                    myCal$ctl59    System.Web.UI.WebControls.TableCell
                        myCal$monthSelector    System.Web.UI.WebControls.DropDownList
                        myCal$yearSelector    System.Web.UI.WebControls.DropDownList
                    myCal$ctl60    System.Web.UI.WebControls.TableCell
                        myCal$nextMonth    System.Web.UI.WebControls.LinkButton
                        myCal$ctl61    System.Web.UI.LiteralControl
                        myCal$nextYear    System.Web.UI.WebControls.LinkButton
                        .....
 

Here is the relevant C# code in the DLL.

            // Set up DropDownList navigators for the title
            DropDownList monthSelector = new DropDownList();
            monthSelector.ID = "monthSelector";
            for (int i=0; i<12; i++) {
                monthSelector.Items.Add(new ListItem(DateTimeFormatInfo.InvariantInfo.MonthNames[i],
                                                     (i+1).ToString()));
            }
            monthSelector.AutoPostBack = true;
            monthSelector.EnableViewState = false;
            monthSelector.SelectedIndex = VisibleDate.Month-1;
            monthSelector.DataBind();
 
            DropDownList yearSelector = new DropDownList();
            yearSelector.ID = "yearSelector";
            for (int i=VisibleDate.Year-10; i<=VisibleDate.Year+10; i++) {
                yearSelector.Items.Add(new ListItem(i.ToString(), i.ToString()));
            }
            yearSelector.AutoPostBack = true;
            yearSelector.EnableViewState = false;
            yearSelector.SelectedIndex = 10;
            yearSelector.DataBind();
 
            // Set up postback listeners for each control.
            prevYear.Click += new EventHandler(OnPrevYearClick);
            prevMonth.Click += new EventHandler(OnPrevMonthClick);
            nextMonth.Click += new EventHandler(OnNextMonthClick);
            nextYear.Click += new EventHandler(OnNextYearClick);
            monthSelector.SelectedIndexChanged += new EventHandler(OnMonthSelectorChanged);
            yearSelector.SelectedIndexChanged += new EventHandler(OnYearSelectorChanged);

Can anyone rescue me from my dufus-ness?

[Plater]

The DropDownLists successfully AutoPostBack. But I can't get my SelectedIndexChanged handler to execute to save my life.

How do you know that they're posting back if their even never fires?
How do you know the event never fires?
Are you binding the datasource in the page_load (or analogue) function?

[revbart]

Plater, thanks so much for taking the time to help me. The spirit of fraternal volunteerism on these boards never ceases to amaze me. I'll try to answer your questions.

How do you know that they're posting back if their even never fires?

Answer: I know that AutoPostBack is working because whenever I change one of the DropDownLists, I witness a page reload.

How do you know the event never fires?

I know that the handler never executes because the very first line of the handler writes to the TraceContext indicating that it is beginning to execute. This message never appears in the trace. Also, of course, the desired calendar navigation never takes place.

Are you binding the datasource in the page_load (or analogue) function?

I'm calling DataBind in OnInit. The DDLs have the same value every time--they do not bind to any external datasource. As you can see in the original code, they simply present the months of the year and a list of years surrounding the present year.

The code creating the DDLs lies within a helper method (I think I named it something like CreateNavigationInterface) that is called by CreateChildControls().

[revbart]

Normally I would suspect that the controls hadn't been added to the Control tree when the event came looking for it, but since the LinkButton objects are directly adjacent to these DropDownList controls--even surround them--the fact that the LinkButton controls catch all their events just fine makes me relatively certain that these DDLs are also present while we're raising postback events.

[revbart]

AHA!

I fixed it myself. The problem was one too many DataBind()s In the Page_Load method on the actual page itself, I allow for the querystring to set the VisibleDate on the initial load. I had put the loading of the variable in an if-block, but not the DataBind() call for the PreachingCalendar. Thus, DataBind() was executing every time at Page_Load, whether a PostBack or not. The EnsureChildControls at LoadPostData was painstakingly putting all the controls in place, only to have them obliterated at the beginning of Page_Load, just before RaiseChangedEvents. LinkButtons, I have learned, do it differently (get their events at a different time.

So, am I an even bigger Dufus for puzzling so long over this when the answer was right there in front of me all along? I'll let you decide. Right now, I really don't care, because all that matters is this functional code in front of me.

[Plater]

I'm claiming victory

Are you binding the datasource in the page_load (or analogue) function?