I have a custom class (ServerSideValidator.vb) that validates user input on server side (it doesn't use any of the .NET built in validators, therefore Page.Validate() is not an option for me). I am calling the Validate() method on page.IsPostback event and the class performs without any problem
My issue is, when validation fails (returns false), I want to stop the postback event handler from firing, but load the page along with all the controls and user-input values in them. If I do, Response.End(), the page comes up blank. I can programmatically instruct the page to go to the previous page (original form before postback), but it loses all user-inputs.
I thought of creating a global boolean variable in the page code behind file and check the value before performing any postback method, but this approach takes away from my plan to provide all functionalities inside the class itself. The page object is being referenced to ServerSideValidator.
Seems like all the postback related properties/variables I come across inside Page class are 'Readonly' and I can't assign value(s) to control/prevent postback event from firing.
Any idiea on how I can accomplish this? Please let me know if you need further details
It's probably easier to post back to the same page every time and do your validation there, specifically on the page load event. If the validation fails, you're already on the correct page and don't have to go to a previous page. If the validation succeeds, then you can redirect to another page if you wish, in which case you probably don't need any data.
Edit: This isn't exactly what you asked for, but I have a feeling it will do what you want while fitting into the existing ASP.NET validation design. See http://www.dotnetcurry.com/ShowArticle.aspx?ID=197 and https://web.archive.org/web/20211020145934/https://www.4guysfromrolla.com/articles/073102-1.aspx
Basically, you create a custom class just like you have now, but inherit from BaseValidator. To follow your design, you can create an enum called ValidationType which has Alphabetic, Alphanumeric, etc. In your custom class, create a property called ValidationType that uses the ValidationType enum. Of course you have to add all the validation logic. Then in your aspx page, you can add your custom validator to the page and set ValidationType="Alphabetic", etc. with full IntelliSense support.
Since you use BaseValidator, all the regular validation techniques will work including Page.Validate(), Page.IsValid, etc. You can even create client-side validation JavaScript if you wish.
Having said this, someone has probably already done most of this for you.
Related
I'm retro-fitting a .aspx page with AJAX functionality (using VB, not C#). The codebehind populates the page with data pulled from a web-service. The page has two panels that are populted (with different data, of course) in this way. On a full page refresh, one or both panels might need to be populated. But populating Panel 2 can take a long time, and I need to be able to update panel 1 without refreshing Panel 2. Hence the need for AJAX (right?)
The solution I've come up with still has the old .aspx page with .aspx.vb codebehind, but introduces a Generic Handler (.ashx) page into the mix. Those first two components do the work on the user's first visit or on a full page refresh, but when AJAX is invoked, the request is handled by the .ashx page.
First question: Is this sound architecture? I haven't found a situation online quite like mine. Originally, I wanted to make the .aspx page into the AJAX handler by having the codebehind implement IHttpRequest, and then providing "ProcessRequest" and "IsReusable" methods, but I found I couldn't separate a regular visit to the page from an AJAX request, so my AJAX handlers took over even on the first visit to the page. Second question: Am I right to think that this approach (making the .aspx page do double-duty as the AJAX handler) will never work? Is it impossible to tell whether we're getting a full-page request or a partial-page (AJAX) request?
If the architecture is good, then I need to dynamically generate a lot of HTML in the .ashx file, right? If that is right, should I send HTML back to the client, or should I encode it in some way? I've heard of JSON encryption, but haven't figured out how to use it yet. So, Third question: Is "context.Response.Write" the only pipeline for sending data back to the client? And, if so, should I send back HTML or some kind of JSON-encoded objects?
Thanks in advance.
It sounds as if the page requires some AJAX functionality added to the UI.
Suggest using an UpdatePanel for each web form element that needs to have AJAXy refresh
functionality. That'll save you from having to refactor a bunch of code, and introduce a whole lot of HTML creation on your .ashx.
It'll be more maintainable over the long run, and require a shorter development cycle.
As pointed out by others, UpdatePanel would be a easier way - but you need to use multiple update panels with UpdateMode property set as conditional. Then you can trigger the update-panel refresh using any button on the page (see AsyncPostBackTrigger) or even using java-script (see this & this). On the server side, you may decide what has triggered the partial post-back and act accordingly by bypassing certain code if not needed.
You can also go with your approach - trick here is to capture the page output using HttpServerUtility.Execute in your ashx and write it back into the response (see this article where this trick has been used to capture user control output). Only limitation with this approach is that you can only simulate GET requests to your page and so you may have to change your page to accept parameters via query string. Personally, I will suggest that you create a user control that accept parameters via method/properties and will generate necessary output and then use the control on your page and in ashx (by dynmaically loading it in a temperory page - see this article).
EDIT: I am using jquery to illustrate how to do it from grid-row-view.
$(document).ready(function() {
$("tr.ajax-grid-row").click(function() {
$("#hidden-field-id").val($(this).find(".row-id").val()); // fill hidden filed
$("#hidden-button-id").click(); // simulate button click
});
});
You can place above script in the head element in markup - it is assuming that you have decorated each grid-row-view with css class "ajax-grid-row" and each row will have hidden field decorated with css class "row-id" to store row identifier or the value that you want to pass to server for that row. You can also use cell (but then you need to use innerHTML to get the value per row). "hidden-field-id" and "hidden-button-id" are client ids for hidden field and submit button - you should use Control.ClientID to get actual control ids if those are server controls.
JSON is not for that purpose, it is to pass objects serialized with a nice light weight notation, is you need to stream dinamically generated html using ashx, response.Write is what you have. You may want to take a look at MVC
Or you could use jquery if it's just html, the simpliest would be the load function, or you can look into Ajax with jquery. Since the ashx can be served as any resource it can be used in the load function.
I agree with #p.campbell and #R0MANARMY here. UpdatePanel could be the easiest approach here.
But then like me, if you don't want to go the UpdatePanel route, I don't see anything wrong with your approach. However, generating the html dynamically (entirely) at the back end is not a route I'll personally prefer (for the maintainence reasons). I'd rather prefer implementing a solution that will keep the design separate from the data.
I have a website in ASP.NET (WebForms, NOT MVC) which has a survey form divided in several slides. Each slide has a next button that, obviously does a transition (client-side, not post back or remote request) to the next slide.
In each slide I have several ASP.NET controls with their related validators. I want this validators to be triggered when I click the next button (or maybe when each input loses focus?).
I remembered ASP.NET doing client side validation on lost focus, but maybe I'm wrong... (I quit doing ASP.NET development about 3 years now, so I can't remember)
Thanks
UPDATE:
It would be better to make ASP.NET trigger each validator when the associated control lost focus. I remember ASP.NET doing this (or am I dreaming? =P)
First you need to make sure all of your validators have target controls specified using the "TargetControlID" Attribute on the validators.
Then you can set up a validation group per page and specify the group name in your next button and on the controls themselves.
If you are using regular expression validators you can choose them from this website
To Validate Client Side
If you are using custom validators you can create a client function and specify it on the custom validator using the ClientValidationFunction attribute and by setting EnableclientScript = "true" on the custom validator.
Just be sure your client function has sender and args parameters.
It looks like there's a supplied JavaScript function called Page_ClientValidate which should be callable to check the validation manually from JavaScript. I haven't used it, though, so YMMV.
put all your client-side validators into the same validationgroup and with your 'next' button add the same validation group. When you click the button it will automatically trigger all the validators before it does the post-back.
as to manually triggering the validation...
you might also be able to use ValidatorOnSubmit(). I remember doing this in another project but i'm having a hard time finding the code.
It seems that enabling 'SetFocusOnError' on each validator triggers the validation whenever I try to leave the field.
In short decorate your model, now Data Annotations are supported from Asp.Net 4.5
Check my Answer here..Client side webform validations
I know that ASP.NET controls such as the button have the postback event model. And checking whether the page.IsValid is dependent on events and postback in order for the validation to kick in.
But what if I have a button using regular HTML inside my .aspx (and I don't want to use the asp.net button...please do not ask me why) yet still want to take advantage of calling Page.IsValid?
For example, lets say my .aspx page has 2 buttons:
<asp:ImageButton runat="server" ID="cmdPlaceOrder" OnClick="cmdPlaceOrder_Click" ImageUrl="images/someButton.gif" />
and that was there in the page, someone else had created that a while back. In the cmdPlaceOrder we check for Page.IsValid:
protected void cmdPlaceOrder_Click(object sender, EventArgs args)
{
if (!IsValid)
return;
... rest of logic
}
That's standard. Now what if I add a non-ASP.NET button like this in the .aspx page, used to place the order (but for a different kind of order seperate from the existing place order button above):
<img src="images/buttonPayGoogleCheckout.gif" alt="Pay with Google"/>
So on click of the hyperlink, the page posts back to itself (same url). I check the url for a querystring param flag that if set calls the method below that I created which is basically a similar method as the above but with a bit of different logic in it:
protected void PlaceGoogleCheckoutOrder()
{
if (!IsValid)
return;
... rest of logic here, but I can't get to it because there is no event model to allow IsValid to work
}
Obviously I'm not tying in an event model to this therefore once it hits the check for Page.IsValid it errors with the following message at runtime:
Page.IsValid cannot be called before validation has taken place. It should be queried in the event handler for a control that has CausesValidation=True and initiated the postback, or after a call to Page.Validate.
But I still want to be able to call this validation, the validation that's already been setup in our .aspx. I don't want to reinvent the wheel on this and I don't in this case want to use an ASP.NET based button (do not ask me why, I have my reasons and it's too long to get into that).
I want to know how I can still get that Page.IsValid check to work for a non-event driven button using . I'm not sure how to hook up an event to do so that still hooks in after the redirect and allows that code to still validate.
I tried adding Page.Validate(); inside my PlaceGoogleCheckoutOrder() method right before the check for Page.IsValid but I still get the same error.
After looking at MSDN on Page.Validate() (http://msdn.microsoft.com/en-us/library/0ke7bxeh.aspx) and it states "The validation group is determined by the control that posted the page to the server. If no validation group is specified, then no validation group is used."
So that's why nothing happened. So I'm not sure how to get ASP.NET in this case to know about the control (in this case my ) that posted the page to the server so that a validation group IS used. I guess I could add a runat="server" to my ...but doubt that's all I need to do here.
The trick with your normal button is that it never does a post back because your href attribute has some other url there. If you want to check if the page is valid, you have to post back to your page class first to make that check and then redirect from there.
What you can do to make this happen with a normal anchor (<a >) tag is process that anchor's onclick event in javascript, do any client side work you want, and then call the __doPostBack() javascript function.
You can see an example of how to call __doPostBack() on msdn here:
http://msdn.microsoft.com/en-us/library/aa720099(VS.71).aspx
It's from .Net 1.1, but still accurate.
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 wrap my head around asp.net. I have a background as a long time php developer, but I'm now facing the task of learning asp.net and I'm having some trouble with it. It might very well be because I'm trying to force the framework into something it is not intended for - so I'd like to learn how to do it "the right way". :-)
My problem is how to add controls to a page programmatically at runtime. As far as I can figure out you need to create the controls at page_init as they otherwise disappears at the next PostBack. But many times I'm facing the problem that I don't know which controls to add in page_init as it is dependent on values from at previous PostBack.
A simple scenario could be a form with a dropdown control added in the designer. The dropdown is set to AutoPostBack. When the PostBack occur I need to render one or more controls denepending on the selected value from the dropdown control and preferably have those controls act as if they had been added by the design (as in "when posted back, behave "properly").
Am I going down the wrong path here?
I agree with the other points made here "If you can get out of creating controls dynamically, then do so..." (by #Jesper Blad Jenson aka) but here is a trick I worked out with dynamically created controls in the past.
The problem becomes chicken and the egg. You need your ViewState to create the control tree and you need your control tree created to get at your ViewState. Well, that's almost correct. There is a way to get at your ViewState values just before the rest of the tree is populated. That is by overriding LoadViewState(...) and SaveViewState(...).
In SaveViewState store the control you wish to create:
protected override object SaveViewState()
{
object[] myState = new object[2];
myState[0] = base.SaveViewState();
myState[1] = controlPickerDropDown.SelectedValue;
return myState
}
When the framework calls your "LoadViewState" override you'll get back the exact object you returned from "SaveViewState":
protected override void LoadViewState(object savedState)
{
object[] myState = (object[])savedState;
// Here is the trick, use the value you saved here to create your control tree.
CreateControlBasedOnDropDownValue(myState[1]);
// Call the base method to ensure everything works correctly.
base.LoadViewState(myState[0]);
}
I've used this successfully to create ASP.Net pages where a DataSet was serialised to the ViewState to store changes to an entire grid of data allowing the user to make multiple edits with PostBacks and finally commit all their changes in a single "Save" operation.
You must add your control inside OnInit event and viewstate will be preserved. Don't use if(ispostback), because controls must be added every time, event in postback!
(De)Serialization of viewstate happens after OnInit and before OnLoad, so your viewstate persistence provider will see dynamically added controls if they are added in OnInit.
But in scenario you're describing, probably multiview or simple hide/show (visible property) will be better solution.
It's because in OnInit event, when you must read dropdown and add new controls, viewstate isn't read (deserialized) yet and you don't know what did user choose! (you can do request.form(), but that feels kinda wrong)
After having wrestled with this problem for at while I have come up with these groundrules which seems to work, but YMMV.
Use declarative controls whenever possible
Use databinding where possible
Understand how ViewState works
The Visibilty property can go a long way
If you must use add controls in an event handler use Aydsman's tip and recreate the controls in an overridden LoadViewState.
TRULY Understanding ViewState is a must-read.
Understanding Dynamic Controls By Example shows some techniques on how to use databinding instead of dynamic controls.
TRULY Understanding Dynamic Controls also clarifies techniques which can be used to avoid dynamic controls.
Hope this helps others with same problems.
If you truly need to use dynamic controls, the following should work:
In OnInit, recreate the exact same control hierarchy that was on the page when the previous request was fulfilled. (If this isn't the initial request, of course)
After OnInit, the framework will load the viewstate from the previous request and all your controls should be in a stable state now.
In OnLoad, remove the controls that are not required and add the necessary ones. You will also have to somehow save the current control tree at this point, to be used in the first step during the following request. You could use a session variable that dictates how the dynamic control tree was created. I even stored the whole Controls collection in the session once (put aside your pitchforks, it was just for a demo).
Re-adding the "stale" controls that you will not need and will be removed at OnLoad anyway seems a bit quirky, but Asp.Net was not really designed with dynamic control creation in mind. If the exact same control hierarchy is not preserved during viewstate loading, all kinds of hard-to find bugs begin lurking in the page, because states of older controls are loaded into newly added ones.
Read up on Asp.Net page life cycle and especially on how the viewstate works and it will become clear.
Edit: This is a very good article about how viewstate behaves and what you should consider while dealing with dynamic controls: <Link>
Well. If you can get out of creating controls dynamicly, then do so - otherwise, what i whould do is to use Page_Load instead of Page_Init, but instead of placing stuff inside the If Not IsPostBack, then set i just directly in the method.
Ah, that's the problem with the leaky abstraction of ASP.NET web forms.
Maybe you'll be interested to look at ASP.NET MVC, which was used for the creation of this stackoverflow.com web site? That should be an easier fit for you, coming from a PHP (thus, pedal-to-the-metal when it comes to HTML and Javascript) background.
I think the answer here is in the MultiView control, so that for example the dropdown switches between different views in the multi-view.
You can probably even data-bind the current view property of the multiview to the value of the dropdown!
The only correct answer was given by Aydsman. LoadViewState is the only place to add dynamic controls where their viewstate values will be restored when recreated and you can access the viewstate in order to determine which controls to add.
I ran across this in the book "Pro ASP.NET 3.5 in C# 2008" under the section Dynamic Control Creation:
If you need to re-create a control multiple times, you should perform the control creation in the Page.Load event handler. This has the additional benefit of allowing you to use view state with your dynamic control. Even though view state is normally restored before the Page.Load event, if you create a control in the handler for the Page.Load event, ASP.NET will apply any view state information that it has after the Page.Load event handler ends. This process is automatic.
I have not tested this, but you might look into it.