I have a Button_click event. While refreshing the page the previous Postback event is triggering again. How do I identify the page refresh event to prevent the Postback action?
I tried the below code to solve it. Actually, I am adding a visual webpart in a SharePoint page. Adding webpart is a post back event so !postback is always false each time I'm adding the webpart to page, and I'm getting an error at the else loop because the object reference is null.
if (!IsPostBack){
ViewState["postids"] = System.Guid.NewGuid().ToString();
Cache["postid"] = ViewState["postids"].ToString();
}
else{
if (ViewState["postids"].ToString() != Cache["postid"].ToString()){
IsPageRefresh = true;
}
Cache["postid"] = System.Guid.NewGuid().ToString();
ViewState["postids"] = Cache["postid"].ToString();
}
How do I solve this problem?
using the viewstate worked a lot better for me as detailed here. Basically:
bool IsPageRefresh = false;
//this section of code checks if the page postback is due to genuine submit by user or by pressing "refresh"
if (!IsPostBack)
{
ViewState["ViewStateId"] = System.Guid.NewGuid().ToString();
Session["SessionId"] = ViewState["ViewStateId"].ToString();
}
else
{
if (ViewState["ViewStateId"].ToString() != Session["SessionId"].ToString())
{
IsPageRefresh = true;
}
Session["SessionId"] = System.Guid.NewGuid().ToString();
ViewState["ViewStateId"] = Session["SessionId"].ToString();
}
This article could be of help to you
http://www.codeproject.com/Articles/68371/Detecting-Refresh-or-Postback-in-ASP-NET
you are adding a Guid to your view state to uniquely identify each page. This mechanism works fine when you are in the Page class itself. If you need to identify requests before you reach the page handler, you need to use a different mechanism (since view state is not yet restored).
The Page.LoadComplete event is a reasonable place to check if a Guid is associated with the page, and if not, create one.
check this
http://shawpnendu.blogspot.in/2009/12/how-to-detect-page-refresh-using-aspnet.html
This worked fine for me..
bool isPageRefreshed = false;
protected void Page_Load(object sender, EventArgs args)
{
if (!IsPostBack)
{
ViewState["ViewStateId"] = System.Guid.NewGuid().ToString();
Session["SessionId"] = ViewState["ViewStateId"].ToString();
}
else
{
if (ViewState["ViewStateId"].ToString() != Session["SessionId"].ToString())
{
isPageRefreshed = true;
}
Session["SessionId"] = System.Guid.NewGuid().ToString();
ViewState["ViewStateId"] = Session["SessionId"].ToString();
}
}
Simple Solution
Thought I'd post this simple 3 line solution in case it helps someone. On post the session and viewstate IsPageRefresh values will be equal, but they become out of sync on a page refresh. And that triggers a redirect which resets the page. You'll need to modify the redirect slightly if you want to keep query string parameters.
protected void Page_Load(object sender, EventArgs e)
{
var id = "IsPageRefresh";
if (IsPostBack && (Guid)ViewState[id] != (Guid)Session[id]) Response.Redirect(HttpContext.Current.Request.Url.AbsolutePath);
Session[id] = ViewState[id] = Guid.NewGuid();
// do something
}
If you want to detect a refresh on an HTTP GET rather than only POSTs, here's a hacky work-around that, in modern browsers, mostly works.
Javascript:
window.onload = function () {
// regex for finding "loaded" query string parameter
var qsRegex = /^(\?|.+&)loaded=\d/ig;
if (!qsRegex.test(location.search)) {
var loc = window.location.href + (window.location.search.length ? '&' : '?') + 'loaded=1';
window.history.replaceState(null, document.title, loc);
}
};
C#:
public bool IsPageRefresh
{
get
{
return !string.IsNullOrEmpty(Request.QueryString["loaded"]);
}
}
When the page loads, it will change add a QueryString parameter of loaded=1 without reloading the page (again, this--window.history.replaceState--only works in post-archaic browsers). Then, when the user refreshes the page, the server can check for the presence of the loaded parameter of the query string.
Caveat: mostly works
The case where this doesn't work is when the user clicks the Address Bar and presses enter. That is, the server will produce a false-positive, detecting a refresh, when odds are, the user actually meant to reload the page fresh.
Depending on your purposes, maybe this is desirable, but as a user, it would drive me crazy if I expected it to reset the page.
I haven't put too much thought into it, but it might be possible to write some magic in order to distinguish a refresh from a reset via the address bar using any/all of:
SessionState (assuming SessionState is enabled) and the value of the loaded QueryString parameter
the window.onbeforeunload event listener
keyboard events (detecting F5 and Ctrl + R to quickly change the URL back to removing the loaded QueryString parameter--though this would have a false-negative for clicking the browser's refresh button)
cookies
If someone does come up with a solution, I'd love to hear it.
Another way to check page refresh. I have written custom code without java script or any client side.
Not sure, it's the best way but I feel good work around.
protected void Page_Load(object sender, EventArgs e)
{
if ((Boolean)Session["CheckRefresh"] is true)
{
Session["CheckRefresh"] = null;
Response.Write("Page was refreshed");
}
else
{ }
}
protected void Page_PreInit(object sender, EventArgs e)
{
Session["CheckRefresh"] = Session["CheckRefresh"] is null ? false : true;
}
Related
I have problem with my iframe asp.net page.
Browser url containst parameter which I need to use in my iframe page.
Obviously I can't get access via .NET so I came up with the idea that at the end of the Page_Load method add sth like that :
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
bool isReloaded = Request.QueryString.GetValue<bool>("reloaded");
ContentId = Request.QueryString.GetValue<int>("contentId"); //I need this value
if (!isReloaded)
{
StringBuilder js = new StringBuilder("<script language='javascript'>");
js.Append("var last = window.top.location.href.substring(window.top.location.href.lastIndexOf('/') + 1, window.top.location.href.length); ");
js.Append("window.location.href = window.location.href + '?reloaded=true&contentId=' + last;");
js.Append("if(window.location.href.indexOf('reloaded=true') == -1) window.location.reload();");
js.Append("<" + "/script>");
Response.Write(js.ToString());
}
}
}
In shortcut I use Javascript to get value I need and fire reload() but with changed QueryString.
Page_Load is firing again and now I have bool isReloaded filled with true.
The condition (!isReloaded) blocks that this time javascript will not be added to Response.
I don't know why, but Page_Load fires again, this time without added parameters so it's the same situation as at the beginning and again is adding JS etc.
Result is that Page_load fires endlessly.
What did I do wrong ? What is the reason ?
if you have a look at your code, you have this line:
js.Append("if(window.location.href.indexOf('reloaded=true') == -1) window.location.reload();");
you are checking the location.href for the 'reloaded' var, but note that your page is reloaded as soon as you change the location, and your script keeps executing before it is done, so it results in reloading of the page over an over again without the query string.
remove this line and it should work fine.
another thing though, i changed your code a little bit to register the script on page instead of response.write it,
it shouldnt make any difference, but if your code still doesnt work then try my version:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
bool isReloaded;
int ContentId;
bool.TryParse(Request.QueryString["reloaded"],out isReloaded);
int.TryParse(Request.QueryString["contentId"],out ContentId); //I need this value
if (!isReloaded)
{
StringBuilder js = new StringBuilder();
js.Append("var last = window.top.location.href.substring(window.top.location.href.lastIndexOf('/') + 1, window.top.location.href.length); ");
js.Append("window.location.href = window.location.href + '?reloaded=true&contentId=' + last;");
ExecScript(js.ToString());
}
}
}
void ExecScript(string script)
{
Page page = HttpContext.Current.CurrentHandler as Page;
if (page != null && !page.ClientScript.IsClientScriptBlockRegistered("AttachedScript"))
{
page.ClientScript.RegisterClientScriptBlock(page.GetType(), "AttachedScript", script, true);
}
}
Thanks for help.
Now I have sth like that and it's ok.
StringBuilder js = new StringBuilder("<script language='javascript'>");
js.Append("var last = window.top.location.href.substring(window.top.location.href.lastIndexOf('/') + 1, window.top.location.href.length); ");
js.Append("if(window.location.href.indexOf('reloaded=true') == -1) window.location.href = window.location.href + '?reloaded=true&contentId=' + last;");
js.Append("<" + "/script>");
I didn't know that editing location executes reload automatically ;)
Thanks again
I am perplexed, and maybe I am just familiar with the properties of pageLoad, IsPostBack, or IsCallback. I created a Boolean variable called "first" and set it to True.
First time through PageLoad, there is a line of code if first = False, if so, write = true.
Then I have a Run_write routine attached to a button, when it runs, if the user response Yes, to the initial question, I make another group of radio buttons visible and set first to false. (i ran this in debug, and I know it hits this line of code) ... so the write to sql is ignored because write == false and the window reappears with the new set of Buttons... Great!
Furthermore, I go through the PageLoad routine again, and it hits the line if (!first), set write to TRUE. my issue is first has been re-set to true? What am I missing?
Note, I was able to work around this by utilizing whether the new set of buttons is checked, but I may not want to go this route, and I do want to understand what is going on.
code is below.
namespace MEAU.Web.Components.SupportCenter
{
public partial class feedback : System.Web.UI.Page
{
String login;
String myurl;
String response;
String s_call;
String p_ship;
String wrnty;
Boolean write;
Boolean first = true;
protected void Page_Load(object sender, EventArgs e)
{
login = Sitecore.Security.Accounts.User.Current.Profile.Email;
myurl = Request.QueryString["value"];
s_call = "No";
p_ship = "No";
wrnty = "No";
// Hide the question Buttons
scall.Visible = false;
parts.Visible = false;
wrnt.Visible = false;
lit.Visible = false;
write = false;
if (!first)
write = true;
}
protected void Run_Write(object sender, EventArgs e)
{
// Get Reponse
if (yes.Checked)
{
response = "Yes";
// Display the quesiton buttons, and Hide the NO button
scall.Visible = true;
parts.Visible = true;
wrnt.Visible = true;
lit.Visible = true;
no.Visible = false;
first = false;
// Did this Prevent a Service call?
if (scall.Checked)
{
s_call = "Yes";
write = true;
}
// Did this Prevent a parts shipment?
if (parts.Checked)
{
p_ship = "Yes";
write = true;
}
// Is this under warranty?
if (wrnt.Checked)
{
wrnty = "Yes";
write = true;
}
// write = true;
}
if (no.Checked)
{
response = "No";
write = true;
}
if (write == true)
{
SqlConnection conn = new SqlConnection(Sitecore.Configuration.Settings.GetConnectionString("feedback"));
SqlCommand cmd = new SqlCommand("Insert_fb", conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#login", login);
cmd.Parameters.AddWithValue("#url", myurl);
cmd.Parameters.AddWithValue("#response", response);
cmd.Parameters.AddWithValue("#dateTime", DateTime.Now);
cmd.Parameters.AddWithValue("#serviceCall", s_call);
cmd.Parameters.AddWithValue("#partsShipment", p_ship);
cmd.Parameters.AddWithValue("#warranty", wrnty);
try
{
conn.Open();
cmd.ExecuteNonQuery();
Response.Write("<script type='text/javascript'>parent.$.fancybox.close();</script>");
Response.Write("<script type='text/javascript'>return false;</script>");
}
catch (Exception ex)
{
throw new Exception("Error on file update" + ex.Message);
}
finally
{
conn.Close();
}
}
}
}
}
Every HTTP request to your site creates a new instance of your page class.
Instance state is not preserved.
Instead, you need to store the state in session or ViewState, depending on what you want to apply to.
Page_Load will be called every time your server is requested for the page. This includes post-backs.
You can check IsPostBack to see if the current Page_Load execution is for the first display of the page, or a subsequent post-back.
protected void Page_Load(object sender, EventArgs e)
{
if (this.IsPostBack)
{
// Do first-time things
}
else
{
// Do non-first-time things
}
}
Note that the particular instance of your page object will not persist from access to access. So there may be some information that you need to initialize every time the page is called.
Every time you visit the page, you're creating a new instance of the class.
To distinguish a page load from a user clicking a button vs. a user arriving on the page for the first time, you want to check the IsPostBack property.
So rewrite your if along the lines of
// Code that always executes
if (IsPostBack)
{
// Code that only executes on initial page load
}
else
{
// Code that only executes when a postback event occurs
// e.g. A user clicks on a button.
}
There are some ways by which you can maintain the state or value of the controls, so I have been maintaining the Viewstate of the controls in the not is postback, as check of
(!IspostBack) // means when page loads first time
and whatever written in the else means when postback occurs in which you can maintain the viewstate of the objects.
Also we can use the session, if Viewstate is not used.
Rykiel,
the basic concept of the web is (state-less), and that why you have to handling, but anyway you can read about page life cycle I recommend you read it http://www.codeproject.com/Articles/20659/The-ASP-NET-Page-Lifecycle-A-Basic-Approach
you can use
if(!isPostBack)
{
first=true;
this portion of code only run when the page is requested first time
}else
{
first = false;
}
if you change the value of control in the page or click a button isPostBack will be true. but if you refresh the page or hit F5 you page will be requested again and isPostBack will be false;.
also you can use cookies or session variable (I also recommend do not load too much the Session Variable). try to read the prior link and you will be more clear where put your code to get the best performance.
J.S.
The answers on here are good, but technical. I will try to explain a little of what is happening.
When a browser requests your page, and on the server, a new instance of your class is created.
ASP.NET then runs the rest of the page, starting with your page_load. This will call all your other functions and then render the HTML as a response to your request and send it back to the browser. I like to explain this as a disconnected environment. Once the response is sent, everything is disposed of in a sense. Your variables, previous work, etc... are all gone. The Server as far as it is concerned, never expects to get anything from the browser again... its done its job. It took your request for a page, created a result and posted it back to the browser. Done.
So, think of your code as a new request each time it is called.
You can use the IsPostback as stated by ThatBlairGuy, because that will return true if you are responding to a postback from the browser, meaning that it has already served up this page to the browser on the previous postback.
I have a 4.0 webpage with a button click that runs a server side process that takes about 5-10 seconds to run. I thought I’d be smart and search for some code that made the button hide and showed an animated gif image while the process was running. I got this working but started to notice “file being used by another process” errors being thrown server side (part of the process is deleting a directory). I debugged through and started to see what appeared to be a second button event click being fired at the same time. Turns out that the piece of Js code I added to refresh the page to allow the animated gif to run seems to be firing the server click event a second time. I had to call the Js SetTimeOut() method to get the gif image running, it's this that is appearing to cause the problem.
I did a bit of searching to try to find a different approach to getting the animated gif to run, but couldn’t find one, so I went for the ambulance at the bottom of the cliff approach and decided to add a server side timestamp into session and only proceed with my code if it is more than 20 seconds since session was last set.
I’ve had some very erratic results with this approach and any input would be appreciated.
Is there a better way I can get the gif running?
Has anyone else come across this issue of the event firing twice?
Why should my lock not work first time through?
Any suggestion of a better approach to do this is appreciated, Thanks!
Logging results:
First time through (no session existing)
2011-06-21 11:46:14.8968|DEBUG|FileViewer.copyfiles|Count = 1 & Locked = False
2011-06-21 11:46:14.8968|DEBUG|FileViewer.copyfiles|Count = 2 & Locked = True
2011-06-21 11:46:19.0619|DEBUG|FileViewer.copyfiles|Count = 1 & Locked = False
2011-06-21 11:46:19.0619|DEBUG|FileViewer.copyfiles|Count = 2 & Locked = True
2011-06-21 11:46:23.1959|DEBUG|FileViewer.copyfiles|Count = 3 & Locked = True
2011-06-21 11:46:28.8119|DEBUG|FileViewer.copyfiles|Count = 3 & Locked = True
Run again:
2011-06-21 11:49:47.7798|DEBUG|FileViewer.copyfiles|Count = 1 & Locked = False
2011-06-21 11:49:47.7798|DEBUG|FileViewer.copyfiles|Count = 2 & Locked = True
2011-06-21 11:49:55.9697|DEBUG|FileViewer.copyfiles|Count = 3 & Locked = True
2011-06-21 11:49:59.8697|DEBUG|FileViewer.copyfiles|Count = 1 & Locked = True
2011-06-21 11:49:59.8697|DEBUG|FileViewer.copyfiles|Count = 3 & Locked = True
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
PostBackOptions optionsSubmit = new PostBackOptions(btnGo);
btnGo.OnClientClick = "HideControlOnClick(this);";
btnGo.OnClientClick += ClientScript.GetPostBackEventReference(optionsSubmit);
}
}
protected void btnGo_Click(object sender, EventArgs e)
{
bool locked = true;
if (Session["ClickTime"] == null || (DateTime)Session["ClickTime"] < DateTime.Now.AddSeconds(-20))
{
Session["ClickTime"] = DateTime.Now;
locked = false;
}
WriteToLog(1, locked);
if (Page.IsValid && !locked)
{
locked = true;
WriteToLog(2, locked);
// Do all my processing
}
WriteToLog(3, locked);
}
<script language="javascript" type="text/javascript">
function HideControlOnClick(btnGo)
{
// IE uses className for the css property.
btnGo.setAttribute('className', 'hide');
document.getElementById('MainContent_imgWait').setAttribute('className', 'show');
setTimeout("UpdateImg('MainContent_imgWait','Images/loading.gif');",50);
}
function UpdateImg(ctrl, imgsrc)
{
var img = document.getElementById(ctrl);
img.src = imgsrc;
}
</script>
I think its better use some web debugger tools to track the request. I suggest use the Fiddler
I suspect that issue here is probably nothing to do with animated gif but button being pressed twice (i.e. two clicks getting registered instead one). You can try disabling the button to supress the second click (yet another way is to have flag at button level) - for example,
btnGo.OnClientClick = "return HideControlOnClick(this);";
function HideControlOnClick(btnGo)
{
if (btnGo["My_Is_Clicked"]) {
// already clicked, ignore
return false;
}
btnGo["My_Is_Clicked"] = true;
...
return true;
}
I've solved the issue by dropping all of the relevant controls into an update pannel, this seems to allow the animated gif to run without calling the setTimeout("UpdateImg('MainContent_imgWait','Images/loading.gif');",50); JS method. Working fine now with the server event only firing once.
The issue is most likely that you're using a server side button control (since you're referencing it server side), and those fire a postback when they're clicked typically (hard to say without knowing the exact object you're using). Use an HTML input to fire your client side event, do your work, and then perform the postback from your JS code (with an appropriate ID to catch on the server side).
Something like this server side:
/// <summary>
/// Page init event, setup the core of the page.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected override void Page_Init(object sender, EventArgs e)
{
try
{
// See if we're in a postback.
if (IsPostBack)
{
// If we have a target...
if (Request.Params["__EVENTTARGET"] != null)
{
// See what the target is.
switch (Request.Params["__EVENTTARGET"])
{
case "btnGo":
// Maybe make this a parameterless method rather than an event handler to avoid parameters that you don't need.
btnGo_Click(null, null);
break;
}
}
}
}
}
And client side:
function Go() {
// Show loading...
// Call server.
__doPostBack("btnGo", "My Args");
}
EDIT: As an alternative I think you can also add "return false;" after the client side event, such as:
btnGo.OnClientClick = "HideControlOnClick(this); return false;";
and that should stop the postback as well.
i have a webform that generates a file, but when i click the button that produces the postback to generate the file Once it finish if i press Refresh (F5) the page resubmit the postback and regenerates the file, there's any way to validate it and show a message to the user or simply DO NOTHING!
thanks :)
The simpler way will be to use Post Rediret Get pattern.
http://en.wikipedia.org/wiki/Post/Redirect/Get
Make sure to check out External Links on that Wikipedia article.
the browser should warn them if they hit refresh on a page that has been postbacked. how i handle it though is in the session track what i have done so i don't repeat certain actions. a simple flag should suffice.
Check for the existence of the file in question in your postback logic and only create the file if the file doesn't already exist:
if (false == System.IO.File.Exists(filename))
{
// create the file
}
else
{
// do whatever you do when the file already exists
}
i wrote a solution for this problem and here it is if anyone needs it.
protected void Page_Load(object sender, System.EventArgs e)
{
/*******/
//Validate if the user Refresh the webform.
//U will need::
//A global private variable called ""private bool isRefresh = false;""
//a global publica variable called ""public int refreshValue = 0;""
//a html control before </form> tag: ""<input type="hidden" name="ValidateRefresh" value="<%= refreshValue %>">""
int postRefreshValue = 0;
refreshValue = SII.Utils.convert.ToInt(Request.Form["ValidateRefresh"]); //u can use a int.parse()
if (refreshValue == 0)
Session["ValidateRefresh"] = 0;
postRefreshValue = SII.Utils.convert.ToInt(Session["ValidateRefresh"]); //can use a int.parse()
if (refreshValue < postRefreshValue)
isRefresh = true;
Session["ValidateRefresh"] = postRefreshValue + 1;
refreshValue = SII.Utils.convert.ToInt(Session["ValidateRefresh"]); //can use a int.parse()
/********/
if (!IsPostBack)
{
//your code
}
}
you just have to evaluate:
if (!isRefresh)
PostFile();
else
{
//Error msg you are refreshing
}
I have a boolean variable declared at the top of a class and when a radio button is selected on a page, the variable gets set to true, but when the page is reloaded, the variable gets reset back to false. One way I have handled this was by using the static keyword, but I am not sure if this is the best way to handle this. Here is the class where I tried doing things in the Page_Load event, but it is still resets the variables to false.
public class SendEmail
{
bool AllSelected;
protected void Page_Load(object sender, EventArgs e)
{
if(!Page.IsPostBack)
{
AllSelected = false;
}
}
protected void rbAll_SelectedIndexChanged(object sender, EventArgs e)
{
if(rbAll.SelectedValue == "All")
AllSelected = true;
}
public Send()
{
if(AllSelected)
{
//Send Email. Never runs because AllSelected is always false;
}
}
}
When the page gets reloaded, a new instance of your page class is created so any values from the last server interaction are lost. Put the value into viewstate if you want it to persist across postbacks:
bool AllSelected
{
get
{
object o = ViewState["AllSelected"];
if(o == null) return false;
return (bool)o;
}
set
{
ViewState["AllSelected"] = value;
}
}
The ViewState collection is written in a hidden element into the form in the client's browser, and posted back and restored the next time they click a button or do any other "postback" type action.
Every time asp.net serves a page, it creates a new instance of the page class. This means that AllSelected will always be auto initialized to false.
My suggestion, unless there is something I don't see here, is to just call Send() from your SelectedIndexChanged method.
You need your variable to be stored. I'd suggest storing it in ViewState or if you want to stay away from ViewState, hide it in a form element on the page.
Also, I'm not seeing where Send is being called.
Your boolean is an instance variable, so it will get the default value (which is false for bools) every time you create a new instance of your class.
Remember, every request to your page uses a brand new instance of your page class. This includes postbacks.
Not to jump down on you or anything...but why not just check if
rbAll.SelectedValue == "All"
in your send function?
No storage...no populating the ViewState or Session with data that isn't needed...
I don't really know if this is going to be handy in asp.net but I create a new bool in property.settings so that it remembers the bool whenever I close or restart the application. But I think this is more for winforms.