We have a user who is having problems with a ASP.NET app. The user hasn't been available to gather many details, but at this point our best guess is that the PostBack is not occurring. Something is going wrong between when the user clicks the LinkButton and when the HTTP Request is supposed to be made.
(User does have JS enabled)
Beyond solving the immediate problem, it might be helpful for posterity to assemble the canonical list of things that can break PostBack behavior of ASP.NET controls.
If you have say a button that has a postback event as well as a javascript event on click, if the javascript event that is fired returns false postback will be stopped.
I would first check that your <form> tags are well formed and that you don't have nested <form> tags. Both times I've debugged something to do with postback this turned out to be the problem. It's confusing because it's a browser dependent issue.
Having a self-closing <script /> tag can stop postbacks occurring. Get the user to send you any javascript errors from their log. There is actually a decent JS debugger in IE8 (about the only good thing in it!).
a form with no method attribute, or method note being set to POST
an onsubmit event handler that does not return true
trying to submit the form programatically, but unable to locate the form by id as there is another element with the same id on the page
Related
I've heard different stories about ASP.NET and JavaScript: that it works fine with Javascript turned off, that only some parts don't work, and that nothing works at all.
How exactly are ASP.NET applications affected if JavaScript is turned off in a client's browser? What parts don't work (if any)?
For example, will RequiredFieldValidators still work? What about UploadControls? AJAX UpdatePanels and AsyncPostBack's? FileUploads? Do page codebehinds still run?
Forgive my ignorance, I can't seem to find much about the issue that is in-depth.
Client-side validation and Ajax won't work, including async postbacks and any control that requires Javascript in order to work.
Server-side validation (which should always happen anyway) and full postbacks and such should always work, and i think a FileUpload control will as well. The biggest difference would be that someone wouldn't see that the data they entered happened to be invalid til the form was submitted.
LinkButtons don't work because they render out a javascript: target.
If you use GridView controls with ButtonColumns then these won't work as the buttons are javascript too. One way around this is to use a TemplateColumn and add <asp:Button> objects inside it.
Also GridView paging and sorting is JavaScript out-the-box so you'd have to write custom paging and sorting.
Also any control with AutoPostback set to true (e.g. a DropdownList) will not auto-postback. You will be able to catch the SelectedIndexChanged but ONLY when the next postback happens.
Any control that "does something" on the client side without a full page request going back to the server(ie. the whole page reloading) is done via JavaScript , and will not work with JavaScript turned off.
Remember HTML is static, so anything that "changes" in the browser window other than CSS hover effects or anything that calls back to the server without a full page reload, is done via JavaScript, and you cannot expect that to work with JavaScript disabled on the client.
Ok, I thought I understood these topics well, but I guess not, so hopefully someone here can clear this up.
Page.IsAsync seems to be broken. It always returns false.
But ScriptManager.IsInAsyncPostBack seems to work, sort of.
It returns true during the round trip for controls inside UpdatePanels. This is good; I can tell if it's a partial postback or a regular one.
ScriptManager.IsInAsyncPostBack returns false however for async Page Methods. Why is this? It's not a regular postback, I'm just calling a public static method on the page.
It causes a problem because I also realized that if you have a control with AutoPostBack = false, it won't trigger a postback on it's own, but if it has an event handler on the page, that event handler code WILL run on the next postback, regardless of how the postback occurred, IF the value has changed.
i.e. if I tweak a dropdown and then hit a button, that dropdown's handler code will fire. This is ok, except that it will also happen during Page Method calls, and I have no way to know the difference.
Any thoughts?
As Tjaart points out, Page.IsAsync has nothing to do with AJAX! See MSDN for a bit more info about IsAsync and see http://msdn.microsoft.com/en-us/magazine/cc163725.aspx for a fuller description of async pages].
Page methods are web services by a different name. The ScriptManager will emit the necessary JS boiler plate to make creating an XHR that invokes the web service very easy but that's all ScriptManager has to do with them really.
As the MSDN page states, ScriptManager.IsInAsyncPostBack will only be true if the request is in "partial rendering mode" so ScriptManager.IsInAsyncPostBack will be false when you are executing a page method because that request has not been spawned as a result of a partial postback (i.e. an UpdatePanel refreshing its contents).
Now it sounds like you are getting server side event handlers being executed as an apparent result of calling a page method from JS. AFAIAA, invoking a page method using javascript should not cause the page to go through its normal page lifecycle - so Page load, init etc. and these events should not be executing. So that is strange.
Suggestion: -
See Anz's comments and Dave's replies here encosia.
Could it be that you are having similar problems to Anz? i.e. The page method is invoked and but then your page is posting back immediatly after?
This is so because ASP.NET Ajax and ASP.NET Callbacks are two different things and are implemented differently. Unfortunately you have to use both Page.IsAsync and ScriptManager.IsInAsyncPostBack.
Page.IsASync probably returns whether the page was set as Async in the page directive
<%# Page Language="vb" Async="true" ...
The autopostback flag is so that you don't get a postback after every single control action, so the user can fill in an entire form and then only create the postback and trigger all the related code.
It's not really weirdness, they designed it this way so that the server side code will always be synchronized with the client side. So if you make a drop down list selection on the page and a postback occurs then that drop down list change executes it's own code along with the control that triggered the postback. You may want to read up more on the ASP .Net page lifecycle. it made things much more clear for me.
I currently have a simple form that when you click the "save" button will persist it to the database.
I would like to use JQuery to do the callback for me and popup a "Save completed" div window/div of some sort.
My only problem is how do I call the btnSave_Click() event from JQuery?
If I use PageMethods the method would have to be static and therefore lose access to my textboxes and other page controls?
Thanks,
Goosey
Are you explicitly trying to avoid passing the values of the input controls? because that would be much easier.
Using a lightweight jQuery call to do the post but then expecting a full control hierarchy in the code behind to pull data out? What's the intent here? If you require that, it would probably be easier just to submit the page, and register javascript to run to pop the success message up on load.
Personally, I think the page method route and $.ajax or $.post is a much cleaner, separate way to solve the issue. That way you can just show the popup as part of the success callback.
You can use onClientClick
Have a look at the jQuery Form Plugin, it can change existing forms into Ajax forms.
You need to set __EVENTTARGET to the id of the control that you want to simulate causing the postback if you want to use the same handler. I seem to recall having to replace the underscores with dollar signs as well, but I could be wrong on that. The hidden inputs, __EVENTTARGET and __EVENTARGUMENT, are used by the framework to identify which control caused the postback. There's a nice discussion of the server side issues in this blog post, though it doesn't talk about AJAX. Google for __EVENTTARGET and postback for more info.
Ok, so the problem is as follows: I'm using jQuery's AJAX in order to make behind the scene calls within the page (on events such as voting an item) and changing the content in the appropriate element. The problem occurs when I mix AJAX with ASP.net's AJAX, more precisely when I try to do a postback AFTER I've used jQuery on the page to perform an action. The page's viewstate is changed and validation fails (which would seem somewhat normal as a matter of fact).
My question is: can I disable the validation somehow so that I can perform postbacks combined with the chaged page viewstate? So far searching on how to disable it yielded no results.
A more practical example is on a comments page where I allow voting the comments and posting new comments as well. So should a user vote a comment and THEN post his own, the page's contents is changed, and thus validation fails. Also, I've tried placing the comment form within an update panel as to prevent the entire page from posting, but it still fails.
Of course I could use an alternate route and have a different page for handling the event and just call that via jQuery's AJAX, but I was wondering if I could do this by combining ASP.net and jQuery.
Thanks in advance.
If you want to disable viewstate verification, you can set it at the page or config level by using Page.EnableViewStateMac = false.
http://msdn.microsoft.com/en-us/library/system.web.ui.page.enableviewstatemac.aspx
It's not necessarily a good idea though because the validation functionality is there to protect from viewstate tampering, which you'll be turning off...
If you're running into issues with invalid viewstate because of jQuery ajax calls, one option is to consider using the Ajax controls, such as the UpdatePanel. You can wrap certain controls and mark the UpdatePanel as conditional to ensure a small round trip. This will not interfere with viewstate and allow you to continue to use viewstate validation and ajax at the same time.
There may be ways to use jQuery ajax calls and not interfere with viewstate validation. Others may be able to highlight this approach.
I need the ability to temporarily turn off the partial page update behavior for an ASP.NET Ajax / UpdatePanel based page. (The reason is to circumvent the issue where IE blocks "automatic file downloads" for downloads generated as a result of this postback, but I don't want to distract from my original question)
I looked at the client side javascript libraries hoping to find a switch somewhere. I think a solution might involve using javascript to override the 'onclick' event handler for the control that acts as the trigger, and then calling "submit" on the form itself..
Also, using the EnablePartialRendering property on the server-side ScriptManager control won't work because that is done when the page is being built. I need to be able to do this as a result of switching a drop down list box.
Any ideas?
Cheers!
/ Sean
Well, after much trial and error, I found two approaches that seemed to work:
Use Javascript to manually submit the top level form associated with the page. This usually has the ID of "form1".
Create a button that is outside of any UpdatePanels and use Javascript to click the button.
I wound up using the second approach, since it allowed me to handle the event with a specific routine without the need to guess that my postback came from a Javascript call.
This is an example of the code that performed the postback:
...
if (isDownload) {
document.getElementById('FullPostbackSubmitter').click();
return;
}
...
Hope this helps someone else!
You can set the EnablePartialRendering property of your ScriptManager to false.