I'm writing my first ASP.net control. I would like to know to know how to make the control postback when the user clicks something (but in general, I want to know how to make arbitrary events make the control postback).
Update Thanks for the answer. However, upon more Googling, it sounds like I'm supposed to make my control call a JavaScript function called __doPostBack. It says that I'm supposed to pass __doPostBack the UniqueID of the control.
You implement IPostBackEventHandler. The linked MSDN page includes a code example.
Related
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.
ASP.NET has a number of nice features regarding making data input pages:
Adding input controls is easy (<asp:...).
The system automatically generates member variable for the controls.
Post-backs automatically populate the members variable with the returned values.
and some not so nice bits
post-backs seem to be tied to JavaScript for even the simplest of cases. For instance, with statically defined pages, using only basic controls, that are known at compile time.
My questions:
Is is possible to get the first list without the second?
What features does that JavaScript give the user?
What does that JavaScript actually do?
What is the technical reasons that it's used even in trivial cases?
As it happens my assumption were in error: See here
It really depends on the types of controls you are trying to use here -- the only ones that implement javascript are those that can't natively cause a postback (ie, an input/submit button are the only two that can). If you are using a LinkButton, ImageButton, or anything that you set "AutoPostBack = true" on will turn javascript on in order to cause a postback.
Other controls can also potentially use javascript if they are more advanced such as the Calendar. The technical reason for using javascript here is to provide automated postback when the controls require more advanced server interaction -- think about it, a link is meant to only ever be a link and if we're trying to make it operate as a button we have to force it to do just that through javascript interaction.
So that being said, yes you can definitely use ASP.NET without it having javascript you just have to avoid the controls that implement it by including functionality you couldn't possibly have without it. You can just as easily add HTML controls and add the runat="server" attribute and gain member variables to the control from code-behind.
Here's what came to my mind:
What features does that JavaScript give the user?
Client side validation.
What does that JavaScript actually do?
For exmaple, it ensures that the correct (server-side) event handlers are called, by setting the __EVENTTARGET hidden field.
Is is possible to get the first list without the second?
You can use normal HTML controls instead of the ASP.NET controls. Then on the server-side, you can read the control's values from the Form collection.
I assume you mean the javascript associated with an <asp:Button /> control, right?
In addition to the reasons mentioned by Fooberichu, the javascript can also help with ASP.NETs client side validation framework.
But I think it's primary use is to alert the framework what events it should fire on the postback in the page behind.
So if you had two buttons on the form, SaveButton and DeleteButton, the javascript helps the framework know whether it should execute the SaveButton_Click event or DeleteButton_Click event.
Hope this helps.
So I have a number of user control dynamically added to a page, and user interaction with these dynamically added user controls need to be handled by the control's parent.
Is this what is referred to as "event bubbling"?
How do I do that in VB?
Thanks in advance.
First, you have several complex issues here and my initial thought is that you should separate them and attack each on its own until you have it working and then add them into the final solution. For instance, don't try to start off by dynamically creating your user control and getting it to expose and fire an event. The dynamic part of this problem could get in the way and cause your events not to work but you would never know which is the problem. Instead my recommendation is you focus on events in VB.NET and getting them to work from a statically created user control. Then once you have this all working, move to making the user control dynamically created.
As far as understanding events in VB.NET, I highly recommend the MSDN samples. Start with this simple example: How to: Raise an Event (Visual Basic) and then follow through with the other samples that are linked to from that page. Then once you have learned creating your own events in VB.NET, then look into adding a usercontrol dynamically.
Event bubbling is when a parent control handles an event from a child. So, yes, this is what you are trying to do.
I am not sure of VB but in c# you can use following
id.event+=eventhandler yourEvent;
My first response to this kind of question is always this - why are you dynamically adding the controls? Could they go into a repeater (where this becomes a lot simpler), or must they be programatically handled?
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.
I'm trying to code what I think is a fairly routine AJAX pattern using TreeViews and UpdatePanels. My situation is this:
I have a TreeView within an UpdatePanel. I have a Literal within another UpdatePanel. When the user clicks on a node within the TreeView, the contents of the Literal are updated. Now, since the whole thing is asynchronous, there is of course a time lag between the click and the update of the Literal contents. During this time, I'd like to do two things:
1) Show an UpdateProgress, and
2) Clear the contents of the Literal
This is so that the user doesn't have to stare at the old contents while the new text is getting loaded asynchronously.
I can't seem to figure out an easy way to accomplish (2). I've been reading up on client side callbacks and using GetCallbackEventReference, but it seems like a very complicated approach to what is seemingly a simple problem.
Ideally, I would like to leave TreeView alone to do it's work. I don't want to get the contents myself and add them to the TreeView using JS. I'd just like to detect the node change event at the client side, clear up the Literal, and let TreeView go about with its normal operation.
Is this possible? Or are client call backs my only option?
You'll be wanting to play with the PageRequestManager from the ASP.NET AJAX library. Here's the MSDN reference for the PRM - http://msdn.microsoft.com/en-us/library/bb311028.aspx.
Just be for warned Microsoft have stated that the TreeView can be problematic within the UpdatePanel and you'll also want to be very careful of the performance, particularly if you have a large TreeView (see my article on optimising the UpdatePanel performance - http://www.aaron-powell.com/blog.aspx?id=1195). You should really look at something like a jQuery plugin (eg: http://bassistance.de/jquery-plugins/jquery-plugin-treeview/).
But to actually answer you're question you need to:
Have a BeginRequest event handler which will then clear your literal and can even show a Loading (I'm not a fan of the UpdateProgress, I prefer much more granular control I get from doing it myself)
Use the EndRequest event to ensure that the Loading component vanises
You could also make the TreeView a AsyncPostbackTrigger of the 2nd UpdatePanel on the page, or just call the Update method on it during the async postback of the TreeView
i had the same problem and fixed it by creating a hidden html element that overlaps the area i want to hide. I show it onSubmit and hide it in the window.onload during a postback. It's not pretty, but it works and should be fast.