How to figure out which updatepanel was updated on clientside

Question

For my particular problem i need to find a way on the client side which UpdatePanel has been updated. To figure that out on the ServerSide is not quite hard (there's a plentitude of SO Questions about this), but i'd prefer a more generic solution for the client side.

I tried the following things:

I inspected the PageRequestManager client object without success
I checked the value of $("#__EVENTTARGET").val() in hope for any ID to work with (always empty)

My scenario is that i've written a script for a control which is executed via Sys.Application.add_init, which is why EVENTTARGET hidden field may not be filled yet.

My idea would be mixing techniques of ASP.MVC (IHttpModule) and Webforms (like here) to get a clean and generic solution.

Thus my plan is to access params for the request and inject a JS into the response which declares the eventtarget for me.

What i am wondering about now is: Is this a good solution or am i unaware of some existing functionality to figure out which updatepanel was updated? (Or is this an ugly solution and you know a better way to do this)

@TimSchmelter Yes. Basically i have a nested structure of UpdatePanels and some Telerik Controls and need to figure out, which one has been updated to limit my script calls depending on that information — Dbl, Jul 25 '14 at 13:49

score 1 · Answer 1 · edited Jun 20 '20 at 09:12

One way I know to get the names of update panels that are going to be updated after postback is to use Sys.WebForms.PageRequestManager pageLoading Event.

From MSDN:

Raised after the response from the server to an asynchronous postback is received but before any content on the page is updated.

To get a list of update panels you need to call get_panelsUpdating function:

<script>
    Sys.WebForms.PageRequestManager.getInstance().add_pageLoading(pageLoadingHandler);

    function pageLoadingHandler(sender, args) {

        console.log("Following panels are going to be updated:");
        var panelsToBeUpdated = args.get_panelsUpdating();
        for (var index in panelsToBeUpdated) {
            console.log(panelsToBeUpdated[index].id);
        }
    }
</script>

Alternatively you can intercept asynchronous postback before anything would be sent to server using Sys.WebForms.PageRequestManager initializeRequest Event. I think it would be possible to save the list of update panels to some variable/field/whatever which is available for your script.

<script>
    Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(initializeRequestHandler);

    function initializeRequestHandler(sender, args) {

        var panelsToBeUpdated = args.get_updatePanelsToUpdate(); // This function returns client ids of update panels
        for (var index in panelsToBeUpdated) {
            console.log(panelsToBeUpdated);
        }
    }
</script>

Anyways, almost all page event handlers sender parameters are having _postBackSettings field which could be used to get the list of panel ids affected by postback:

sender._postBackSettings.panelsToUpdate

The only downside of this field is _ in its name which means that it is "private" and should be avoided to be accessed directly.

helpful but not viable for my scenario. i've used this method before in another scenario. unfortunately this time i am bound to getting it to work within add_init and there's no similar method to call on the args of the handler. — Dbl, Jul 27 '14 at 12:24
@AndreasMüller maybe I'm mistaken but isn't `add_init` handler called only once, i.e. the first time page loaded and not after each async postback? — Alexander Manekovskiy, Jul 27 '14 at 17:43
You are correct about that. However in my scenario i bind it to init, as well as firing it at render time, making my script run at both times. Unfortunately this is part of the reason why i need to find a way to figure out the updatepanel in question. (Also i can't use add_load, because some of the controls inside my control use that event and i need my script to be executed before that) — Dbl, Jul 28 '14 at 08:01
@AndreasMüller please see updated answer. New idea is to save list of update panels right before postback and then retrieve them in your script. — Alexander Manekovskiy, Jul 29 '14 at 07:04

score 0 · Accepted Answer · answered Jul 29 '14 at 08:32

0

In the meantime i modified my production solution but for this particular issue you can indeed implement IHttpModule and inject code to update information in javascript, in case someone stumbles into a similar scenario.

answered Jul 29 '14 at 08:32

Dbl

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How to figure out which updatepanel was updated on clientside

2 Answers2