Develop Reference

Submit a form from code behind

I'm having trouble implementing a functionality on my c#/asp.net app.
I have a form with a RadioButtonList and a submit button.
The RadioButtonList is generated on Page_Load() from a list of objects I retrieve from the database.
I would like to automatically submit the form if there is only 1 object in the list.
I have access to my Form object, to the submit button etc... but I can't seem to find a solution (in the end I'm looking for a kind of form.Submit() ) method.
Does anyone have an idea of how I could do this ?
Thanks in advance !
EDIT >> Here is the code :
.aspx : http://pastebin.com/0E6T7dqH
.aspx.cs : http://pastebin.com/54payZJP
EDIT2 >>>
As it seems there is no way to do what I wanted to do at first, I ended up using a session variable with a response.redirect()
Source :
http://dotnetslackers.com/Community/blogs/haissam/archive/2007/11/26/ways-to-pass-data-between-webforms.aspx

Post happens in the client side. As in Page_Load you are currently executing in the server side, just call the code you want to execute on post.
Edit: For actually going to another aspx
public void Page_Load(object sender, EventArgs e) {
if(!IsPostback && OnlyOneItem) {
Server.Transfer("TheOtherPage.aspx");
}
}
Server.Transfer will maintain the entire request, so your post data will be available.
http://msdn.microsoft.com/en-us/library/system.web.httpserverutility.transfer.aspx

Try something like this
In your Page_Load
if(!IsPostBack)
{
if(check for only one object)
{
//your submit code
}
}

I actually had to do something similar, once. Here is a way you can do it.
Asp.Net buttons have a property called PostBackUrl, and it does exactly what you would expect - it controls where the form will post if you click the button.
You can also use the RegisterStartupScript function to render javascript on the page.
Now, with these two pieces, you can achieve your goal.
if(!IsPostBack)
{
if(results == 1)
{
button.PostBackUrl = "next page's url"
//Register script to click the button using RegisterStartupScript
}
}
Now, having shown you this, I will warn you it may not make for the best user experience. When I did it, it was for a very specific case that had no other solution. The page will actually post back to the user, and they will see the page for a moment before the javascript to click the button takes effect. Additionally, when you set a button's PostBackUrl, that means that when it is clicked, your entire form will be posted to the page specified. The code behind for the current page will not fire at all, so if you have any validation, it won't run.
There's nothing wrong with letting the user click the button to submit the form even if they only have one choice. In my experience, users like to feel like they are in control on the system; they don't like it when pages just do things without their input.
Also, there is not really anything wrong with putting the information the next page needs into the session or even a database table, and using Response.Redirect. It's a fairly common practice and works reliably in most scenarios.

call clientside javascript from asp.net c# page

I have a c# asp.net page and an update function which will update the database. In this function I would like to call some client side javascript. I've read a lot about registering a start up script in page_load() but this is always trigger on page load (funny that!)
How would I register then call a script inside my update function? Triggered when a user clicks the "update" button. I have tried the following (inside my function)
protected void doUpdate(object sender, EventArgs e) {
string jScript;
jScript = "<script type=text/javascript>alert('hello');<" + "/script>";
ClientScript.RegisterStartupScript(GetType(), "Javascript", jScript);
}
but it isn't fired. Any ideas? Many thanks.
[update]
It's now working - the function looks like this
protected void doUpdate(object sender, EventArgs e) {
ScriptManager.RegisterStartupScript(this, GetType(),"Javascript", "cleanup();",true);
}
Cleanup() is the javascript function in my HTML. Thanks for the help guys :)

If the control causing the postback is inside an UpdatePanel you need to use
ScriptManager.RegisterStartupScript

You can't 'execute' client side scripts from the web server (the client knows who the server is, but not the other way around).
The only way to overcome this limitation is by a. create a long-polling process that requests something from the server, the server doesn't complete the request till it has something to return (then client side it makes another request).
What you are really looking for is websocket (duplex) enabled communication. You can check out alchemy websockets or SignalR (has a pretty nice library with dynamic proxy generation).
The reason why that 'script always works on Page_Load' is because it effectively injects your script tag into the html returned for the page requested.

Your Update button is likely using the standard ASP Button behavior, meaning it is type="submit" when it is rendered. Since that's the case, you can just use:
Page.ClientScript.RegisterOnSubmitStatement
Keep in mind that will register a script for every postback, not just the Update button. So, if you only want some javascript run on clicking Update, you would need to check if the EventTarget is UpdateButton.ClientID. Also, RegisterOnSubmitStatement always adds the <script> tags, so don't include those in the javascript statement.
An even easier solution, the ASP Button itself also has an OnClientClick property. This will run client-side code (javascript) when the button is clicked in the browser.

Call an event handler on another page

Simple question here, but I've got a nagging feeling that there's a more interesting solution than the one I've chosen:
Page Two consists of a dropdown, and the change event is handled to execute some query.
protected void ddlSavedQueries_SelectedIndexChanged(object sender, EventArgs e)
{
/* stuff happens */
}
Page One is a home page, where I'm providing another version of that dropdown. I'd like the change event in this case to redirect control to Page Two, and then execute the event handler.
My cheap solution is just a Redirect with a querystring value that is handled on page load. Am I missing a more interesting approach?

If you don't want to ugly things up with a querystring value, I suppose you could put something in Session and pick it up on Page_Load of the second page (and then clear it out of Session). Not exactly an awesome improvement though.

Does the same page always get displayed when you change that dropdown? If so, consider using client side javascript to redirect to the correct page, then fire any logic on the subsequent page in the page_load event. Example using jQuery:
$(function() {
$("select.classyouneedtodefine").change(function() {
document.location.href = "somepage.aspx?value=" + $(this).val();
});
});
haven't tested the above...just shooting from the hip

Refresh Page C# ASP.NET

Is there a Page.Refresh type of command to refresh a page?
I don't want to redirect to the page or refresh in JavaScript.

I think this should do the trick (untested):
Page.Response.Redirect(Page.Request.Url.ToString(), true);

Careful with rewriting URLs, though. I'm using this, so it keeps URLs rewritten.
Response.Redirect(Request.RawUrl);

Response.Redirect(Request.Url.ToString());

You can just do a regular postback to refresh the page if you don't want to redirect. Posting back from any control will run the page lifecycle and refresh the page.
To do it from javascript, you can just call the __doPostBack() function.

Use:
Response.Redirect(Request.RawUrl, true);

You shouldn't use:
Page.Response.Redirect(Page.Request.Url.ToString(), true);
because this might cause a runtime error.
A better approach is:
Page.Response.Redirect(Page.Request.Url.ToString(), false);
Context.ApplicationInstance.CompleteRequest();

Depending on what exactly you require, a Server.Transfer might be a resource-cheaper alternative to Response.Redirect. More information is in Server.Transfer Vs. Response.Redirect.

I use
Response.Redirect(Page.Request.Path);
If you have to check for the Request.Params when the page is refresh use below. This will not rewrite the Request.Params to the URL.
Response.Redirect(Page.Request.Path + "?Remove=1");

I use # for Current page url address at Redirect to Refresh and that working currectly.
What do you think about this:
Response.Redirect("#")

Call Page_load function:
Page_Load(sender, e);

To refresh the whole page, but it works normally:
Response.Redirect(url,bool)

ASP.Net: Page_Load() being called multiple times

I don't know alot about ASP.Net but I'm trying to make a new control for a message box. You enter some info and press a button.
However, for some bizarre reason when the button is pressed, Page_Load() gets called a second time, and all of the member variables are reset to null! I need those variables, and Page_Load() has not reason to be called a second time! Of course the callstack is useless.

Remember, in ASP.Net every time you cause a postback of any kind, including handling events like button clicks, you're working with a brand new instance of your page class that must be rebuilt from scratch. Any work you've done previously to build the page on the server is gone. That means running the entire page life cycle, including your page load code, and not just the click code.
Always two there are, no more, no less. A request and a response.

When the page posts back, the Page_Load method is called. Then, once the server actually processes the page and sends you a new one based on changes, the Page_Load is called again, actually the first time on the new page sent to you.
So if you are pulling data in the Page_Load event or setting some values, enclose it in the following block:
if(!Page.IsPostBack)
{
}
to preserve some of your state. Otherwise, the instructions that you put into the Page_Load event will execute every time.
It helps to review the ASP.Net page lifecycle :)

As Joel mentioned, instance variables will be lost once the page is sent back to the client. However, there are various methods of storing the values of your variables so you can retrieve them later. This page on State Management is a good starting point if you want to learn more.

Any tag/element which requires url reference like img, anchor, object etc must be checked for the empty reference.
e.g. href="", url="", src="" are some common errors.

This code works for me:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
if (Session["something"] == null)
{
Session["something"] = "1";
}
else
{
Session["something"] = null;
//your page load code here
}
}
}

For me, the issue was a bit complicated, but I found that the
protected override void OnPreRender(EventArgs e)
handler is only called once, so it's safer to put some actions in there if it's not too late in the pipeline for you.

An extension of #user3207728's response, I found this link explains it well and has a simple solution...
http://www.aspdotnet-suresh.com/2010/04/detect-browser-refresh-to-avoid-events.html
Unfortunately checking just for if (!Page.IsPostBack) is not enough as IsPostBack will always be FALSE on a refresh.

Just a shot in the dark but maybe add this after your page_load:
if (!IsPostBack)
{

you can use sessions or viewstate to retain the values of variables..
if you want to redirect to a different page , use session[]
else if you want to stay on the same page , use viewstate[]

In my Case the Problem Was Related to Iframe, One Time I removed the Iframe Everithing Work Fine
<iframe id="pdf2"
src="#"
width="100%"
height="100%">
</iframe>