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
Related
I have written some codes in !IsPostBack block. This code is getting executed when the page loads for the first time. That is fine. But the problem is, when I refresh the page by hitting the f5 key this executes again which I don't want to do. I have searched many articles and found difference between PostBack and refresh. I know about this. But my question is difference between !IsPostBack and Refresh. Can we write some code which executes only when the page loads for the 1st time not when we refresh the page. By the way I have written my !IsPostBack block inside Page_Init() method and I am using c# for codebehind. Thanks.
Refersh and IsPostback are somewhat unrelated:
Refresh in browser generally mean "re-run last action that resulted in this page". Usually it causes GET request, but it as well can cause POST if page was shown as result of postback. Side note: you often can find sites warning you not to refresh page during non-reversible operations like "charge my credit card" as it may trigger duplicate post.
IsPostBack simply states that request come to server as POST, not GET.
Combining that you can get Refresh that triggers either branch of if (IsPostBack) check. In most cases so server will receive GET request and hence execute !IsPostBack branch.
If you really need to detect if page was rendered once already - setting cookie or writing information into Session would be reasonable solution.
Please change your code behind code as given below.
Boolean IsPageRefresh;
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
ViewState["postids"] = System.Guid.NewGuid().ToString();
Session["postid"] = ViewState["postids"].ToString();
}
else
{
if (ViewState["postids"].ToString() != Session["postid"].ToString())
{
IsPageRefresh = true;
}
Session["postid"] = System.Guid.NewGuid().ToString();
ViewState["postids"] = Session["postid"].ToString();
}
}
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.
Is there a way to force a postback in code?
I'm looking to force the raising of a postback from a method in the c# code behind my asp.net web application.
You can try redirecting to same page.
Response.Redirect(Request.RawUrl);
A postback is triggered after a form submission, so it's related to a client action...
take a look here for an explanation:
ASP.NET - Is it possible to trigger a postback from server code?
and here for a solution:
http://forums.asp.net/t/928411.aspx/1
Simpler:
ScriptManager.RegisterStartupScript(this.Page, this.Page.GetType(), "DoPostBack", "__doPostBack(sender, e)", true);
Here the solution from http://forums.asp.net/t/928411.aspx/1 as mentioned by mamoo - just in case the website goes offline. Worked well for me.
StringBuilder sbScript = new StringBuilder();
sbScript.Append("<script language='JavaScript' type='text/javascript'>\n");
sbScript.Append("<!--\n");
sbScript.Append(this.GetPostBackEventReference(this, "PBArg") + ";\n");
sbScript.Append("// -->\n");
sbScript.Append("</script>\n");
this.RegisterStartupScript("AutoPostBackScript", sbScript.ToString());
No, not from code behind. A postback is a request initiated from a page on the client back to itself on the server using the Http POST method. On the server side you can request a redirect but the will be Http GET request.
You can use a data-bound control like the Repeater or ListView, re-bind it to a list of control properties as needed, and let it generate the controls dynamically.
As an alternative, you can use Response.Redirect(".") to re-load the same page.
By using Server.Transfer("YourCurrentPage.aspx"); we can easily acheive this and it is better than Response.Redirect(); coz Server.Transfer() will save you the round trip.
You can manually call the method invoked by PostBack from the Page_Load event:
public void Page_Load(object sender, EventArgs e)
{
MyPostBackMethod(sender, e);
}
But if you mean if you can have the Page.IsPostBack property set to true without real post back, then the answer is no.
I've got a page with a Timer that is being used as a trigger on an UpdatePanel. The page also contains a TabContainer and several TabPanels. Look at this question for more information. Basically, I've got an UpdatePanel as the element in each TabPanel's ContentTemplate, and the UpdatePanel is triggered by the Timer.
My page displays data by reading a database on each tick. I've got the following code running on each Timer.Tick in my codebehind:
protected void timeRefresher_Tick(object sender, EventArgs e)
{
UpdateLivePageTitle();
}
The UpdateLivePageTitle() function reads the new information from the database and sets Page.Title accordingly. However, this information is of course not sent to the browser because there is no full page postback--only an async postback to the update panels. As a result, my page title is not being updated until the whole page is being posted back, which destroys the purpose of using UpdatePanels in the first place.
I figure there would be a way to do this by using the document.title JS element and call that from within UpdateLivePageTitle(). But as of now, I haven't been able to figure out how to do this. I tried using the following in my UpdateLivePageTitle() function:
string updatePageTitleScript = String.Format("document.title = '{0}'", newPageTitle);
ToolkitScriptManager.RegisterStartupScript(this.Page, this.Page.GetType(), "UpdatePageTitle", updatePageTitleScript, true);
But the result of this was that my TabContainer stopped rendering. I'm also not sure that would work with the async partial page postbacks, either. Any ideas?
Thanks!
You forgot the ; from your script.
Oh, and if I remember correctly, the framework should be able to update the title if you just set Page.Title.
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>