I've created a socket listener, and I need to display a div (keep it hidden, then make it visible), when the server detects a certain socket data.
I've tried to use a thread, but it doesn't update the UI in realtime, only if the page is reloaded or if you do a post back.
Here is an example of what I want to do, in this case I only want to update a textbox with codebehind data, I would like to do it without ajax, javascript or jQuery, if possible.
Code Behind:
protected void Page_Load(object sender, EventArgs e)
{
Thread t = new Thread(TestThread);
t.Start();
}
private void TestThread()
{
for (int i = 0; i <= 1000000000; i++)
{
myTextbox.Text += "1";
}
}
Webpage:
<asp:UpdatePanel runat="server" ID="myPanel" >
<ContentTemplate>
<asp:TextBox runat="server" ID="myTextbox" />
</ContentTemplate>
</asp:UpdatePanel>
what you are trying to do is change the UI (modify client components) from server code (code behind) in asp.net when the server already sent the data to the client.
you have to use client side scripting/coding.
As far as I know, this is not possible without using ajax or JavaScript.
ASP.NET is only responsible for generating the html that is sent from your web-server to the client. Once that html is rendered in the browser, the only way to update the html is via JavaScript.
You can do a Partial Render in WebForms using their AJAX handler without having to write jQuery by enabling a partialRenderingEnabled attribute in the ScriptManager tag. There's no way to do this without scripting or AJAX, the content has to get back to the server to run your code-behind somehow, but at least this way you don't have to write any JavaScript yourself.
For real-time web functionality check out :
SignalR
In a web enviornment, there is no way for the server side to reach out for the client except in the request-response scenario, where the client has to send a request to the server side, the server side handles the request and replies with a response.
EDIT :
SignalR uses the best available technique, websockets when available, if not, AJAX long polling technique in which the client polls(sends a request) to the server, and the server replies only when a certain change to the observed data happens, else SignalR tries repetitve AJAX requests, polling the server over and over until the server replies with the change on the observed data (Worst scenario !).
Also, HTML 5 contains web-sockets, i don't have enough information about it, but it maybe interesting to check out.
With minimal JavaScript you could utilise Server Sent Events for simplex data (from server to client) It doesn't have the overhead of Websockets which has a bit of cost in terms of establishing a connection. However I don't think all browsers are supported but there might be polyfill available for it (library to provide functionality in absence of native support)
Checkout:
http://www.html5rocks.com/en/tutorials/eventsource/basics/
In ASP.NET Threads gets aborted as soon as the page unloads, so this is not possibler you way, sorry.
Your approach could be using AJAX to poll the status from the server on regular intervals. Server on the other hand, will reply according to change in data.
in your ASP.NET Page, add the following script
<head>
<script type="text/javascript" language="javascript">
function poll()
{
var ajax;
if(window.XMLHttpRequest)
ajax = new XMLHttpRequest();
else
ajax = new ActiveXObject("Microsoft.XMLHTTP");
url = "yourPageOrHandler.aspx";
ajax.onreadystatechange = function()
{
if (ajax.readyState == 4 && ajax.status == 200)
{
// success
var receivedText = ajax.responseText;
}
else
{
// error, do the needful
}
}
ajax.open("GET", url, true);
ajax.send();
setTimeout("poll()", 1000); //polls every 1 second, you can change the duration here.
}
</script>
</head>
Start the polling before page finishes
<body>
.
.
.
.
<script type="text/javascript" language="javascript">
poll();
</script>
</body>
Alternatively, you can use the ASP.NET AJAX controls, but that will be heavier compared to JavaScript AJAX.
Glad to help! Please remember to accept the answer if you found it helpful.
Related
I want to create an application for WP8 that shows the content of a web page. I'm not writing the code yet, but but i know that i can take the page content using xpath. My problem is that the content i want to take is not in a single page. I have to press the "Next" button to go to the next page. The code for the button is this.
<td class="pager-next" style="padding:0;margin:0;">
<a id="ctl00_ContentPlaceHolder1_LinkButton2" class="buttondiego buttondiego_small buttondiego_arrow" href="javascript:__doPostBack('ctl00$ContentPlaceHolder1$LinkButton2','')"></a>
</td>
And this is the JS function in the header:
<script type="text/javascript">
//<![CDATA[
var theForm = document.forms['aspnetForm'];
if (!theForm) {
theForm = document.aspnetForm;
}
function __doPostBack(eventTarget, eventArgument) {
if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
theForm.__EVENTTARGET.value = eventTarget;
theForm.__EVENTARGUMENT.value = eventArgument;
theForm.submit();
}
}
//]]>
</script>
Is it possible to go to the next page with my code? How should i do?
You will either have to:
Deeply analyze their JavaScript, and do some reverse engineering on the required POST values to fetch a specific page. You can see what requests are sent using Firebug or Chrome Developer Tools network view. The URL definitely is
<http://www.starcomics.com/UsciteMensili.aspx?AspxAutoDetectCookieSupport=1
but simply POSTing the monitored "interesting looking" fields
__ASYNCPOST:true
__EVENTTARGET=ctl00$ContentPlaceHolder1$DataPager2$ctl00$lnkNextPage
was not sufficient.
Alternatively, you could use some headless browser implementation which actually executes the JavaScript. They will be more complicated to setup and be less performant, but you won't have to care about the logic behind loading the pages any more. I think the most common used headless browser is PhantomJS, but I don't know whether and how to employ it with Windows Phone and C#, you might want to set it up on your own server and proxy the data.
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.
In summary:
I have an ASP.NET web page that causes an AJAX postback to the server. When this event handler runs (in the code behind) it will generate some JavaScript that I then want to run in the client. Not sure how to achieve this.
In Detail:
I have an ASP.NET web page with multiple items displayed on the page.
As a "nice to have", I want to display either a green circle or a red cross next to each item (these differ depending upon each item). Since it isn't vital for the User to see these icons and also because it takes several seconds to work out which icon should be shown for each item, I want to perform this after the page has loaded, so in an AJAX callback.
My thought therefore was this. When creating the page, I would create both icons next to each object and create them with the style of "hidden". I would also make a note of each one's client ID.
Then, when the callback occurs, I fetch the necessary data from the database and then create a JavaScript function that changes the display for each of the icons I want to show from "hidden" to "visible".
I thought I could achieve this using the ScriptManager object.
Here's a very trivial version of my server side code (C#)
void AjaxHandler(object sender, EventArgs e)
{
// call to database
string jscript = "alert('wibble');";
ScriptManager.RegisterStartupScript(this, this.GetType(), "uniqueKey", jscript);
}
Obviously, here I'm just trying to get an alert to fire after the postback has occurred...in real life I'd have my JavaScript function to change the display of all the icons I want to display.
When I run this, the serverside code runs and yet nothing happens in the server.
I have also tried:
ScriptManager.RegisterClientScriptBlock()
Page.RegisterStartupScript()
Page.RegisterClientScriptBlock()
Page.ClientScript.RegisterStartupScript()
Page.ClientScript.RegisterClientScriptBlock()
but none of them work....
FireFox shows the following JavaScript error:
Error: uncaught exception: [Exception... "Node cannot be inserted at the specified point in the hierarchy" code: "3" nsresult: "0x80530003 (NS_ERROR_DOM_HIERARCHY_REQUEST_ERR)" location: "http://localhost/MyWebSiteName/Telerik.Web.UI.WebResource.axd?_TSM_HiddenField_=ctl00_RadScriptManager1_TSM&compress=1&_TSM_CombinedScripts_=%3b%3bSystem.Web.Extensions%2c+Version%3d3.5.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a3de828f0-5e0d-4c7d-a36b-56a9773c0def%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2009.3.1314.20%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3aec1048f9-7413-49ac-913a-b3b534cde186%3a16e4e7cd%3aed16cbdc%3a874f8ea2%3af7645509%3a24ee1bba%3a19620875%3a39040b5c%3af85f9819 Line: 1075"]
Does anyone know if what I am trying to do is even allowed?
If not - what's my alternative?
Thank you
Since your script doesn't have enclosing <script> tags, you need to use this form of RegisterStartupScript:
ScriptManager.RegisterStartupScript(this, this.GetType(), "uniqueKey", jscript, true);
You said your initial goal was:
The idea was that the page would load, data would be sent (AJAX) to the server. The server would then generate some JavaScript based upon this data and send that back to the page. That JavaScript would then run updating the page in a specific way.
Here's a way you can do that:
given:
<asp:ScriptManager runat="server" ID="scriptManager">
</asp:ScriptManager>
<script type="text/javascript">
function endRequestHandler(sender, args) {
var dataItems = args.get_dataItems();
for(var key in dataItems){
if(/^javascript:/.test(dataItems[key])){
eval(dataItems[key].substring("javascript:".length));
}
}
}
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(endRequestHandler);
</script>
<asp:UpdatePanel runat="server" ID="pnl">
<ContentTemplate>
<asp:Button runat="server" ID="btnClick" Text="Click me!" OnClick="btnClick_Click" />
</ContentTemplate>
</asp:UpdatePanel>
You can create a click handler that does this:
protected void btnClick_Click(object sender, EventArgs e)
{
ScriptManager.GetCurrent(Page).RegisterDataItem(this, "javascript:alert('hello world!');");
}
What's happening is during the postback, the page request manager is sent a data item your code-behind. That data-item happens to be a javascript command. After the postback, the client side script manager's endRequest handler is checking for data items. Normally you'd want to see who those items are for, which is apparent by the key of the item (it's the client ID of the control that is the target of the data being sent). In your case, you could load this up with the javascript that you want to fire, tell yourself that it's a javascript because it's prepended, then dynamically evaluate the script.
So in this example, clicking the "Click Me!" button will generate a Hello World prompt whose script was actually created by the code-behind during the postback.
You'll have to be very cautious with this approach until you're comfy - I'd avoid references to "this"...
Happy coding.
B
Okay
The idea was that the page would load, data would be sent (AJAX) to the server. The server would then generate some JavaScript based upon this data and send that back to the page. That JavaScript would then run updating the page in a specific way.
Couldn't get that to work....
I got around this in the following way:
When the page loads, data is sent (AJAX) to the server. This processes the data and serialises the results updating a hidden text element, which goes back to the browser. Meanwhile, I have a JavaScript timer on the page that runs a JavaScript function that was generated when the page first loads. This function looks at the hidden text element. If that element has text (the result of the postback) then it shuts down the timer, deserialises the data and then works out how to update the page.
I have a .Net 3.5 website which uses windows authentication and expires the session using a meta tag on the prerender of my base masterpage class.
protected override void OnPreRender(EventArgs e)
{
base.OnPreRender(e);
if (Response.ContentType == "text/html")
this.Page.Header.Controls.Add(new LiteralControl(
String.Format("<meta http-equiv='refresh' content='{0};url={1}'>",
SessionLengthMinutes * 60, SessionExpireDestinationUrl)));
}
This works well for pages that do full post backs. However there are a few pages in my application where the user does a lot of work that is inside of an update panel. My company's policy is a timeout of 15 minutes. Which means, after 15 minutes of working inside of an update panel page, the user gets redirected to the application splash page.
Is there a way to reset or extend the meta tag on an async postback? Or perhaps a better way to accomplish this entirely?
A better way to accomplish this entirely would be to use javascript. This will prevent meta refresh related issues if your page is bookmarked.
In place of the page META REFRESH use this javascript:
<script type="text/javascript">
var _timerID = setTimeout("window.location='splash-url'", 900000); //15 mins
</script>
When you make a request from the update panel use this javascript:
<script type="text/javascript">
clearTimeout(_timerID);
_timerID = setTimeout("window.location='splash-url'", 900000); //15 mins
</script>
In the past I have used the WebMethod(EnableSession = true) attribute on the methods that respond to AJAX calls
You could use an AJAX request to keep the session alive as well. This will work as long as the user has opened your page in the browser.
See http://808.dk/?code-ajax-session-keepalive
I'm writing a program which has both an ASP.NET configuration system and a Silverlight application. Most users will remain on the Silverlight page and not visit the ASP.NET site except for logging in, etc.
The problem is, I need the session to remain active for authentication purposes, but the session will timeout even if the user is using the features of the silverlight app.
Any ideas?
On the page hosting the silverlight control, you could setup a javascript timer and do an ajax call to an Http Handler (.ashx) every 5 minutes to keep the session alive. Be sure to have your Handler class implement IRequiresSessionState.
I recommend the Handler because it is easier to control the response text that is returned, and it is more lightweight then an aspx page.
You will also need to set the response cache properly to make sure that the browser makes the ajax call each time.
UPDATE
Here is the sample code for an HttpHandler
public class Ping : IHttpHandler, IRequiresSessionState
{
public void ProcessRequest(HttpContext context)
{
context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
context.Response.ContentType = "text/plain";
context.Response.Write("OK");
}
public bool IsReusable
{
get { return true; }
}
}
Then if you use jQuery, you can put this on your host aspx page
setInterval(ping, 5000);
function ping() {
$.get('/Ping.ashx');
}
The interval is in milliseconds, so my sample will ping every 5 seconds, you probably want that to be a larger number. Fiddler is a great tool for debugging ajax calls, if you don't use it, start.
I've actually found a pretty cool hack which essentially embeds an iframe on the same page as the silverlight application. The iframe contains an aspx webpage which refreshes itself every (Session.Timeout - 1) minutes. This keeps the session alive for however long the silverlight app is open.
To do this:
Create an asp.net page called "KeepAlive.aspx". In the head section of that page, add this:
<meta id="MetaRefresh" http-equiv="refresh" content="18000;url=KeepAlive.aspx" runat="server" />
<script language="javascript" type="text/javascript">
window.status = "<%= WindowStatusText%>";
</script>
In the code behind file, add this:
protected string WindowStatusText = "";
protected void Page_Load(object sender, EventArgs e)
{
if (User.Identity.IsAuthenticated)
{
// Refresh this page 60 seconds before session timeout, effectively resetting the session timeout counter.
MetaRefresh.Attributes["content"] = Convert.ToString((Session.Timeout * 60) - 60) + ";url=KeepAlive.aspx?q=" + DateTime.Now.Ticks;
WindowStatusText = "Last refresh " + DateTime.Now.ToShortDateString() + " " + DateTime.Now.ToShortTimeString();
}
}
Now, on the same page as the silverlight app, add this:
<iframe id="KeepAliveFrame" src="KeepAlive.aspx" frameborder="0" width="0" height="0" runat="server" />
Now the asp.net session will remain active while the silverlight app is being used!
The ajax ping / HttpHandler approach is good, but the JQuery $.get function is expecting a json result and throws a javascript parse error.
I modified the Ping HttpHandler to return "{}" instead of "OK" and this worked better.