(ASP.NET)
How do i prevent duplicate records insertion in my database when user refreshs the page after post back. i know it can handle by redirecting the page. it and also handle through the check if same entry exists inside the stored procedure. but this wont full fill requirement sometime. i just want to know is there any other good practice instead redirecting the page.
(I know it can also handle using AJAX, but i am not using AJAX)
Try this
if (!IsPostBack)
{
do something
}
You can use the Page.IsPostBack property
private void Page_Load()
{
if (!IsPostBack)
{
//logic
}
}
In the code example above, if the page is a postback then no code would be executed (the logic).
Related
I would like to know if I can prevent the event bubbling / propagation on the page load based on condition like:
protected override void OnLoad(EventArgs e)
{
// If the user press F5 from the browser
if (IsRefresh)
{
// Here I want to stop propagation/bubbling the events like OnClick of a submit button but without using the button object (I want it generic)
}
else
{
base.OnLoad(e);
}
}
Is this possible?
Prevent the event bubbling has two difficulties - detect the F5 and stop the events - i would simply use the Post/Redirect/Get-pattern:
protected void Button1_Click(object sender, System.EventArgs e)
{
// do what you need to do
// now redirect to the same page,
// then a browser-refresh via F5 won't trigger this event again
Response.Redirect(Request.Url.PathAndQuery);
}
I did once in ASP.NET WebForms project when user press on F5 it'll do something other than refresh, I done this by use jQuery keypress even for the page and call e.preventDefault(); check this
Update:
$(document).ready(){function(){
this.keydown(e){
if (e.which == 116){
e.preventDefault();
window.location.href = "http://foo.com/?IsReferesh=1";
}
};
)};
You can use the QueryString to check if user press F5 and the reflection in Code Behind. If I missed something, then I didn't fully understand your question.
Regarding the specifics of your question, how about inverting it? Maybe add a Load event listener (say, in page Init) only if the condition is not met.
Another option might be doing something like:
this.Load -= MyPageLoadMethod;
You are likely looking at the event itself, not the OnLoad method. Eitherway, I think it is possible, see some options here How to remove all event handlers from a control
There is a big "BUT" though...
Like most people here, I think you are not solving the right problem. I'm sorry the same applies for Emad's solution I think.
Tim nailed it. This answer will try to explain this option more.
The pattern Post-Get-redirect is very popular and very standard. In most of our applications, submitting the same form more than once either by re-clicking the submit button before page loading or refreshing the browser causing another POST call is wrong, so, the practice of redirect after a non-AJAX form submission has become so standard.
Everything else you may try will be no more of a dirty workaround than a proper solution.
--
Now, comes the problem of providing feedback to the user. Ruby On Rails provides a nifty helper for this called Flash helper. It's a message you can set before redirecting (or even in the same page if there is no redirect) and the next time you display it, it'll destroy itself, the next time you call it, you get nothing. so, you display nothing.
ASP.NET MVC has something like this which is TempData. TempData can be stored in many places, by default in the Session, so, if you are redirecting from an MVC action, you can set something like TempData['Message'] , and read it in the next Controller. ASP.NET MVC will handle removing it after the redirect.
So, how about Webforms? There's nothing to prevent you from doing it too. It really isn't rocket science
You can check for URL Referrer whether it is an edit page or not and display message based on that.
You can store a message in Session before redirect, and check for it in every page load, if found, you display it and delete it from Session
If Session is disabled, you can use cookies. You can check the date of the cookie before sending, so that if the redirect never happened (use network dropped or whatever) and use came to the page later in the time he doesn't see an outdated message.
You can also store in Cache (with some key related to user of course, as Cache is application wide), You can then set the Cache expiration to some short period to avoid the problem explained in cookies option
You can also google for Rails Flash-like for ASP.NET Webforms to see what reusable components other people came up with. This result for example came in my search:
http://highoncoding.com/Articles/542_Creating_Rails_Like_Flash_Feature_in__NET_The_Flash_Control.aspx
Check NuGet also maybe there's something there. Again, it's not hard to build your own anyway.
Update:
Another simple approach might be to just redirect to the same URL, this'll cause a GET request and will not run any handler, pretty close to the original implementation of Post-Get-Redirect (yours will be Post-Post-Redirect maybe, kidding), and pretty safe as well.
Something like:
Response.Redirect(Request.RawUrl);
Update 2
Just as mentioned above, if you are running after page init, say in page Load, you can always emove events in a way similar to:
this.SubmitButton.Click -= SubmitButton_Click;
You get the idea...
That's useful if what you want is stop particular events, while the previous bits of the answer were assuming you are trying to stop most of the events.
http://gurustop.net
protected override void OnLoad(EventArgs e)
{
if (!IsPostBack)
{
if (Request.UrlReferrer != null)
if (Request.UrlReferrer.PathAndQuery == Request.RawUrl)
{
// Show Message
}
}
}
protected void Button1_Click(object sender, System.EventArgs e)
{
Response.Redirect(Request.Url.PathAndQuery);
}
Note:
if (Request.UrlReferrer.PathAndQuery == Request.RawUrl) // does not work with chrome
so you can replace it with
if (Request.UrlReferrer.AbsolutePath == Request.Url.AbsolutePath)
static string REFRESH_CHECK_GUID = "REFRESH_CHECK_GUID";
protected void Page_Load(object sender, EventArgs e)
{
if (ViewState[REFRESH_CHECK_GUID] != null && !ViewState[REFRESH_CHECK_GUID].ToString().Equals(Session[REFRESH_CHECK_GUID].ToString()))
{
Response.Redirect("Login.Aspx");
}
Session[REFRESH_CHECK_GUID] = System.Guid.NewGuid().ToString();
ViewState[REFRESH_CHECK_GUID] = Session[REFRESH_CHECK_GUID];
i have a dropdownlist and a listbox both asp.net controls
i am trying to prevent the user add duplciate items to listbox control
i able to block it but i want to display DIV or Alert box saying,"duplciate names are not allowed"
protected void btn_AddRecipientAction_OnClick(object sender, EventArgs e)
{
if (Convert.ToInt32(this.ddlRecipient.SelectedValue) > 0)
{
if (ddlRecipient.Text.Length > 0)
{
//var items = new System.Collections.ArrayList(this.lstRecipient.Items);
for(var i = lstRecipient.Items.Count - 1; i >= 0; --i)
{
if (lstRecipient.Items[i].Text == ddlRecipient.SelectedItem.Text)
{
lstRecipient.Items.RemoveAt(i);
**//alert("duplicate entry not allowed")
//div display the message and disappears after few seconds?**
}
}
ListItem newList = new ListItem();
newList.Text = ddlRecipient.SelectedItem.Text;
newList.Value = ddlRecipient.SelectedValue;
this.lstRecipient.Items.Add(newList);
}
}
}
alert way:
You could use this line assuming you have a ScriptManager
ScriptManager.RegisterClientScriptBlock(this,this.GetType(),"alert","alert('duplicate entry not allowed');",true);
This, however still does a postback since the script is run when the page is loaded again after the click. A better solution is to validate in client using javascript before submitting the page.
What you want is actually two separate things.
You should be validating on in the code behind, checking for duplicates on the post back. Then, use some javascript to do the same check on the client.
You MUST check for duplicates on the server since the user may not have javascript turned on.
Wow! Please don't inject js in the page to alert the user. You should instead have a notification control that receive a dataset of messages like an array then display the messages to the user. You want to separate your concerns.
You can achieve that in js. At the server you can set the array in json in a hidden field and then at the document ready event in js read that json data, parse it and loop on the array and display you messages. If you must you can use alert to display them but you should avoid it since it's so 1990's.
But I would go beyond that. I you do all the processing and validation in javascript before it gets to the server. So you don't rely on a post back to execute your validation. So as soon as the user adds the item it's told that it's a duplicate. Then, once the list is filled by the user he could save with a ajax call or post the page and at the server you parse the list, validate it and save it. If you have to compare the list to one already persisted at the server you can do that there. SOme thing goes wrong? you add the message to the notification control.
Please think about it. Try using a framework like MVC to separate you concerns. I makes the hole thing much faster to develop and so easier to maintain.
To call some JS from the code behind you can use Page.ClientScript property and call the RegisterStartupScript() method
http://msdn.microsoft.com/en-us/library/asz8zsxy.aspx
I'm working on a wizard-like set of page, and I'm relying on cross page postbacks to navigate between them.
I need to be able to trigger the Load event on the previous page in order to save the form data for the page.
I've been told that for situations of this sort all I had to do is access the PreviousPage property in the destination page and this would trigger the load event of the previous page but for some reason this doesn't seem to be working.
Is there anything else I can do to explicitly trigger the load event on the previouspage if the PreviousPage property is not null?
Thanks for your help,
Yong
Have you considered moving whatever persistence logic you're doing in the load of the Previous Page into a method on the page?
That way you can just hit:
if(PreviousPage != null)
PreviousPage.DoThatSavingThing();
Obviously you'd need to type it to get the specific methods you add unless you added those to all pages.
This sounds a little confusing to me, but if you are wanting access to data, it's best to save that data into something that you can easily get to, like the ASP.NET session cache. So instead of going back to a previously navigated page in order to get data, you will cache the data the first time you reach the first page, and then when the user navigates to the 2nd page, it will have access to that information.
To add - I tested using two methods of getting a "strongly-typed" previouspage.
Added a reference to the destination:
Added the PreviousPage directive on the destination:
When accessing the PreviousPage property in the destination, the Load event was fired on the
PreviousPageName page (source).
Example (assuming there is a public property named Test on the PreviousPageName (Source page)):
protected void Page_Load(object sender, EventArgs e)
{
if (PreviousPage != null)
{
//Using a reference, you have to cast:
PreviousPageName x = (PreviousPageName)PreviousPage;
string test = x.Test;
//Using the PreviousPage directive, you do not need to cast:
string test2 = PreviousPage.Test
}
}
I am trying after the btnCreate_OnClick event to reset the form to it's default value just like the first page_load. The problem is after PostBack, every textbox and other controls, reloads the ViewState value. I cannot deactivate viewstate because of server event on DropDownList selection. The only way I found so far is to Redirect to self after the click event, but this loads the page twice and is therefor a bad solution. I have try ViewState.Clear() and update the UpdatePanel, but was unsuccessful.
I could do a loop for all controls and set the txtXXXXX.Text == "", but I'm quite sure it's not the best idea.
Something like Page.Reset() would have been just perfect but it doesn't exist.
Any thought on this problem of mine?
Thanks
If workable, I usually just use Response.Redirect to reload the same page from scratch.
An initial GET request to a page usually costs less than subsequent POSTs anyway, so there's not much reason to avoid it.
We can reset the ASP.NET Form Page with just 2 lines of code
protected void Button_Reset_Click(object sender, EventArgs e)
{
Session["ViewState"] = null;
Response.Redirect("/Roster/DRAC/Create.aspx");
}
Self redirecting gets tricky because of viewstate.
There is an html input type "reset" for buttons, but I'm not sure what or any integration msft has put into viewstate/asp.net for this. It generally works for simple javascript forms.
ex:
<input type="button" value="Reset" onclick="document.<formId>.reset();">
from google ----^
One way, not necessarily ideal, is to reset the values to their defaults using Javascript. If it is a large form, it can be ugly, but will prevent the need to do a self-redirection.
You also might try Server.Transfer instead of Response.Redirect(/self/)
I dont know if this helps but i change the name of every input on the form that i want to get fresh values by using javascript before submiting the form, since the .net page can no longer match the values from the form to the controls for the page it reloads them as if there was no postback. i also append a new value to the form so i know what button submitted the form and use that logic to decide what to load into all the controls and how to process the form data of course.
$("#Bset").children().click(function() { //all the btns click function
$.each($("form").find("input"), function(e,v) { //could filter this to subset of inputs
$(v).attr("name", "_" + $(v).attr("name")); // ctrl1 becomes _cntrl1
});
$("form").append("<input type='hidden' id='b' name='b' value='" + $(this).text() + "' />").submit();
});
then in the code behind
protected void Page_Init(object sender, EventArgs e)
{
id = int.Parse(Request.QueryString["id"]);
bk = db.dc.getDetailBK(id).Single();
if (Request.Form.Count > 0)
doPostBack();
mrl = (from a in db.dc.getMetricQTD(id, null, null, loadSavedGoals) select a).ToList();
}
i can then do things in dopostback that process the form data, interact with the db etc. that may change the values mrl is loaded with and refresh the data in the inputs tied to mrl regardless of wether they were modified or not on the form.
the other alternative would be to tie some buttons to use a webservice to handle your db interaction then call window.location to refresh the page.
$.ajax({
url: "webservice/dbfunction?"
data: {which btn pressed, some form values etc...}
success: function() {window.location("samepage.aspx?id=xxx");}
...
});
this would also avoid having to response redirect on the server side.
In our case the best performance solution was to set manually for each control the default value in the click event ex:
textbox1.Text = null;
textbox2.Text = null;
This avoid the double page_load and the loop. We don't event have to update the UpdatePanel since it executes before render.
Maybe in a more complex web application we would have to Redirect as most people seem to accept this as a solution.
Setting per control the default value was better suited to our case.
Thank you
I need to catch the HTML of a ASP.NET just before it is being sent to the client in order to do last minute string manipulations on it, and then send the modified version to the client.
e.g.
The Page is loaded
Every control has been rendered correctly
The Full html of the page is ready to be transferred back to the client
Is there a way to that in ASP.NET?
You can override the Render method of your page. Then call the base implementation and supply your HtmlTextWriter object. Here is an example
protected override void Render(HtmlTextWriter writer)
{
StringWriter output = new StringWriter();
base.Render(new HtmlTextWriter(output));
//This is the rendered HTML of your page. Feel free to manipulate it.
string outputAsString = output.ToString();
writer.Write(outputAsString);
}
You can use a HTTPModule to change the html. Here is a sample.
Using the answer of Atanas Korchev for some days, I discovered that I get JavaScript errors similar to:
"The message received from the server could not be parsed"
When using this in conjunction with an ASP.NET Ajax UpdatePanel control. The reason is described in this blog post.
Basically the UpdatePanel seems to be critical about the exact length of the rendered string being constant. I.e. if you change the string and keep the length, it succeeds, if you change the text so that the string length changes, the above JavaScript error occurs.
My not-perfect-but-working solution was to assume the UpdatePanel always does a POST and filter that away:
protected override void Render(HtmlTextWriter writer)
{
if (IsPostBack || IsCallback)
{
base.Render(writer);
}
else
{
using (var output = new StringWriter())
{
base.Render(new HtmlTextWriter(output));
var outputAsString = output.ToString();
outputAsString = doSomeManipulation(outputAsString);
writer.Write(outputAsString);
}
}
}
This works in my scenario but has some drawbacks that may not work for your scenario:
Upon postbacks, no strings are changed.
The string that the user sees therefore is the unmanipulated one
The UpdatePanel may fire for NON-postbacks, too.
Still, I hope this helps others who discover a similar issue. Also, see this article discussing UpdatePanel and Page.Render in more details.
Take a look at the sequence of events in the ASP.NET page's lifecycle. Here's one page that lists the events. It's possible you could find an event to handle that's late enough in the page's lifecycle to make your changes, but still get those changes rendered.
If not, you could always write an HttpModule that processes the HTTP response after the page itself has finished rendering.
Obviously it will be much more efficient if you can coax the desired markup out of ASP.Net in the first place.
With that in mind, have you considered using Control Adapters? They will allow you to over-ride how each of your controls render in the first place, rather than having to modify the string later.
I don't think there is a specific event from the page that you can hook into; here is the ASP.Net lifecycle: http://msdn.microsoft.com/en-us/library/ms178472.aspx
You may want to consider hooking into the prerender event to 'adjust' the values of the controls, or perform some client side edits/callbacks.