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  • Asynchronous update design/interaction patterns

    - by Andy Waite
    These days many apps support asynchronous updates. For example, if you're looking at a list of widgets and you delete one of them then rather than wait for the roundtrip to the server, the app can hide the one you deleted, giving immediate feedback. The actual deletion on the server will happen in the background. This can be seen in web apps, desktop apps, iOS apps, etc. But what about when the background operation fails. How should you feed back to the user? Should you restore the UI to the pre-deletion state? What about when multiple background operations fail together? Does this behaviour/pattern have a name? Perhaps something based on the Command pattern?

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  • ASP.NET control event handler not firing on postback?

    - by Polaris878
    I have a control which has an ImageButton which is tied to an OnClick event... Upon clicking this control, a postback is performed and the event handler is not called. AutoEventWireup is set to true, and I've double checked spelling etc.... We haven't touched this control in over a year and it has been working fine until a couple of weeks ago. We have made changes to controls which load this control... so I'm wondering, what kind of changes could we have made to stop this event handler from being called? There is quite a bit of Javascript going on, so this could be the culprit too... Edit: Some clarification... we are dynamically loading the parent control of the ImageButton in the OnLoad event of the page... if that makes sense.

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  • What's the official Microsoft way to track counts of dynamic controls to be reconstructed upon Postback?

    - by John K
    When creating dynamic controls based on a data source of arbitrary and changing size, what is the official way to track exactly how many controls need to be rebuilt into the page's control collection after a Postback operation (i.e. on the server side during the ASP.NET page event lifecycle) specifically the point at which dynamic controls are supposed to be rebuilt? Where is the arity stored for retrieval and reconstruction usage? By "official" I mean the Microsoft way of doing it. There exist hacks like Session storage, etc but I want to know the bonafide or at least Microsoft-recommended way. I've been unable to find a documentation page stating this information. Usually code samples work with a set of dynamic controls of known numbers. It's as if doing otherwise would be tougher. Update: I'm not inquiring about user controls or static expression of declarative controls, but instead about dynamically injecting controls completely from code-behind, whether they be mine, 3rd-party or built-in ASP.NET controls.

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  • How to Retrieve Values of A Dynamically Created Control's Child Controls on PostBack?

    - by Jordan
    Given: I have a custom server control in the markup of an aspx page. This control creates child controls in its CreateChildControls() method (e.g. it retrieves content from a database and based on that content dynamically creates either a CheckBoxList or a RadioButtonList) Now I understand that I cannot access the dynamically created controls on postback unless I add them again on Page_Init or Page_PreInit (as per here). My question is, how do I add them again explicitly in Page_Init or Page_PreInit if they are just going to be added yet again when we get around to calling Render() on each of the custom server controls? I'm very certain this is not a unique problem, so there must be a best practice way of doing it...I just don't know what it is :/

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  • How do I register a Javascript function to run with every postback?

    - by Kevin
    I have a treeview in a user control. I need to run a javascript function with every synch postback to scroll the div it's in to the right position. I've got it working, but I think there has to be a "cleaner" way to do it. In the Page_Load function of the control, I have the following code. Is there a better way to do it? ScriptManager.RegisterStartupScript(this.UpdatePanel1, this.GetType(), "key" + DateTime.Now.Ticks, "RestorePosition();", true);

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  • How to detect a timeout when using asynchronous Socket.BeginReceive?

    - by James Hugard
    Writing an asynchronous Ping using Raw Sockets in F#, to enable parallel requests using as few threads as possible. Not using "System.Net.NetworkInformation.Ping", because it appears to allocate one thread per request. Am also interested in using F# async workflows. The synchronous version below correctly times out when the target host does not exist/respond, but the asynchronous version hangs. Both work when the host does respond. Not sure if this is a .NET issue, or an F# one... Any ideas? (note: the process must run as Admin to allow Raw Socket access) This throws a timeout: let result = Ping.Ping ( IPAddress.Parse( "192.168.33.22" ), 1000 ) However, this hangs: let result = Ping.AsyncPing ( IPAddress.Parse( "192.168.33.22" ), 1000 ) |> Async.RunSynchronously Here's the code... module Ping open System open System.Net open System.Net.Sockets open System.Threading //---- ICMP Packet Classes type IcmpMessage (t : byte) = let mutable m_type = t let mutable m_code = 0uy let mutable m_checksum = 0us member this.Type with get() = m_type member this.Code with get() = m_code member this.Checksum = m_checksum abstract Bytes : byte array default this.Bytes with get() = [| m_type m_code byte(m_checksum) byte(m_checksum >>> 8) |] member this.GetChecksum() = let mutable sum = 0ul let bytes = this.Bytes let mutable i = 0 // Sum up uint16s while i < bytes.Length - 1 do sum <- sum + uint32(BitConverter.ToUInt16( bytes, i )) i <- i + 2 // Add in last byte, if an odd size buffer if i <> bytes.Length then sum <- sum + uint32(bytes.[i]) // Shuffle the bits sum <- (sum >>> 16) + (sum &&& 0xFFFFul) sum <- sum + (sum >>> 16) sum <- ~~~sum uint16(sum) member this.UpdateChecksum() = m_checksum <- this.GetChecksum() type InformationMessage (t : byte) = inherit IcmpMessage(t) let mutable m_identifier = 0us let mutable m_sequenceNumber = 0us member this.Identifier = m_identifier member this.SequenceNumber = m_sequenceNumber override this.Bytes with get() = Array.append (base.Bytes) [| byte(m_identifier) byte(m_identifier >>> 8) byte(m_sequenceNumber) byte(m_sequenceNumber >>> 8) |] type EchoMessage() = inherit InformationMessage( 8uy ) let mutable m_data = Array.create 32 32uy do base.UpdateChecksum() member this.Data with get() = m_data and set(d) = m_data <- d this.UpdateChecksum() override this.Bytes with get() = Array.append (base.Bytes) (this.Data) //---- Synchronous Ping let Ping (host : IPAddress, timeout : int ) = let mutable ep = new IPEndPoint( host, 0 ) let socket = new Socket( AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.SendTimeout, timeout ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, timeout ) let packet = EchoMessage() let mutable buffer = packet.Bytes try if socket.SendTo( buffer, ep ) <= 0 then raise (SocketException()) buffer <- Array.create (buffer.Length + 20) 0uy let mutable epr = ep :> EndPoint if socket.ReceiveFrom( buffer, &epr ) <= 0 then raise (SocketException()) finally socket.Close() buffer //---- Entensions to the F# Async class to allow up to 5 paramters (not just 3) type Async with static member FromBeginEnd(arg1,arg2,arg3,arg4,beginAction,endAction,?cancelAction): Async<'T> = Async.FromBeginEnd((fun (iar,state) -> beginAction(arg1,arg2,arg3,arg4,iar,state)), endAction, ?cancelAction=cancelAction) static member FromBeginEnd(arg1,arg2,arg3,arg4,arg5,beginAction,endAction,?cancelAction): Async<'T> = Async.FromBeginEnd((fun (iar,state) -> beginAction(arg1,arg2,arg3,arg4,arg5,iar,state)), endAction, ?cancelAction=cancelAction) //---- Extensions to the Socket class to provide async SendTo and ReceiveFrom type System.Net.Sockets.Socket with member this.AsyncSendTo( buffer, offset, size, socketFlags, remoteEP ) = Async.FromBeginEnd( buffer, offset, size, socketFlags, remoteEP, this.BeginSendTo, this.EndSendTo ) member this.AsyncReceiveFrom( buffer, offset, size, socketFlags, remoteEP ) = Async.FromBeginEnd( buffer, offset, size, socketFlags, remoteEP, this.BeginReceiveFrom, (fun asyncResult -> this.EndReceiveFrom(asyncResult, remoteEP) ) ) //---- Asynchronous Ping let AsyncPing (host : IPAddress, timeout : int ) = async { let ep = IPEndPoint( host, 0 ) use socket = new Socket( AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.SendTimeout, timeout ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, timeout ) let packet = EchoMessage() let outbuffer = packet.Bytes try let! result = socket.AsyncSendTo( outbuffer, 0, outbuffer.Length, SocketFlags.None, ep ) if result <= 0 then raise (SocketException()) let epr = ref (ep :> EndPoint) let inbuffer = Array.create (outbuffer.Length + 256) 0uy let! result = socket.AsyncReceiveFrom( inbuffer, 0, inbuffer.Length, SocketFlags.None, epr ) if result <= 0 then raise (SocketException()) return inbuffer finally socket.Close() }

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  • Calling Web Service Functions Asynchronously from a Web Page

    - by SGWellens
    Over on the Asp.Net forums where I moderate, a user had a problem calling a Web Service from a web page asynchronously. I tried his code on my machine and was able to reproduce the problem. I was able to solve his problem, but only after taking the long scenic route through some of the more perplexing nuances of Web Services and Proxies. Here is the fascinating story of that journey. Start with a simple Web Service     public class Service1 : System.Web.Services.WebService    {        [WebMethod]        public string HelloWorld()        {            // sleep 10 seconds            System.Threading.Thread.Sleep(10 * 1000);            return "Hello World";        }    } The 10 second delay is added to make calling an asynchronous function more apparent. If you don't call the function asynchronously, it takes about 10 seconds for the page to be rendered back to the client. If the call is made from a Windows Forms application, the application freezes for about 10 seconds. Add the web service to a web site. Right-click the project and select "Add Web Reference…" Next, create a web page to call the Web Service. Note: An asp.net web page that calls an 'Async' method must have the Async property set to true in the page's header: <%@ Page Language="C#"          AutoEventWireup="true"          CodeFile="Default.aspx.cs"          Inherits="_Default"           Async='true'  %> Here is the code to create the Web Service proxy and connect the event handler. Shrewdly, we make the proxy object a member of the Page class so it remains instantiated between the various events. public partial class _Default : System.Web.UI.Page {    localhost.Service1 MyService;  // web service proxy     // ---- Page_Load ---------------------------------     protected void Page_Load(object sender, EventArgs e)    {        MyService = new localhost.Service1();        MyService.HelloWorldCompleted += EventHandler;          } Here is the code to invoke the web service and handle the event:     // ---- Async and EventHandler (delayed render) --------------------------     protected void ButtonHelloWorldAsync_Click(object sender, EventArgs e)    {        // blocks        ODS("Pre HelloWorldAsync...");        MyService.HelloWorldAsync();        ODS("Post HelloWorldAsync");    }    public void EventHandler(object sender, localhost.HelloWorldCompletedEventArgs e)    {        ODS("EventHandler");        ODS("    " + e.Result);    }     // ---- ODS ------------------------------------------------    //    // Helper function: Output Debug String     public static void ODS(string Msg)    {        String Out = String.Format("{0}  {1}", DateTime.Now.ToString("hh:mm:ss.ff"), Msg);        System.Diagnostics.Debug.WriteLine(Out);    } I added a utility function I use a lot: ODS (Output Debug String). Rather than include the library it is part of, I included it in the source file to keep this example simple. Fire up the project, open up a debug output window, press the button and we get this in the debug output window: 11:29:37.94 Pre HelloWorldAsync... 11:29:37.94 Post HelloWorldAsync 11:29:48.94 EventHandler 11:29:48.94 Hello World   Sweet. The asynchronous call was made and returned immediately. About 10 seconds later, the event handler fires and we get the result. Perfect….right? Not so fast cowboy. Watch the browser during the call: What the heck? The page is waiting for 10 seconds. Even though the asynchronous call returned immediately, Asp.Net is waiting for the event to fire before it renders the page. This is NOT what we wanted. I experimented with several techniques to work around this issue. Some may erroneously describe my behavior as 'hacking' but, since no ingesting of Twinkies was involved, I do not believe hacking is the appropriate term. If you examine the proxy that was automatically created, you will find a synchronous call to HelloWorld along with an additional set of methods to make asynchronous calls. I tried the other asynchronous method supplied in the proxy:     // ---- Begin and CallBack ----------------------------------     protected void ButtonBeginHelloWorld_Click(object sender, EventArgs e)    {        ODS("Pre BeginHelloWorld...");        MyService.BeginHelloWorld(AsyncCallback, null);        ODS("Post BeginHelloWorld");    }    public void AsyncCallback(IAsyncResult ar)    {        String Result = MyService.EndHelloWorld(ar);         ODS("AsyncCallback");        ODS("    " + Result);    } The BeginHelloWorld function in the proxy requires a callback function as a parameter. I tested it and the debug output window looked like this: 04:40:58.57 Pre BeginHelloWorld... 04:40:58.57 Post BeginHelloWorld 04:41:08.58 AsyncCallback 04:41:08.58 Hello World It works the same as before except for one critical difference: The page rendered immediately after the function call. I was worried the page object would be disposed after rendering the page but the system was smart enough to keep the page object in memory to handle the callback. Both techniques have a use: Delayed Render: Say you want to verify a credit card, look up shipping costs and confirm if an item is in stock. You could have three web service calls running in parallel and not render the page until all were finished. Nice. You can send information back to the client as part of the rendered page when all the services are finished. Immediate Render: Say you just want to start a service running and return to the client. You can do that too. However, the page gets sent to the client before the service has finished running so you will not be able to update parts of the page when the service finishes running. Summary: YourFunctionAsync() and an EventHandler will not render the page until the handler fires. BeginYourFunction() and a CallBack function will render the page as soon as possible. I found all this to be quite interesting and did a lot of searching and researching for documentation on this subject….but there isn't a lot out there. The biggest clues are the parameters that can be sent to the WSDL.exe program: http://msdn.microsoft.com/en-us/library/7h3ystb6(VS.100).aspx Two parameters are oldAsync and newAsync. OldAsync will create the Begin/End functions; newAsync will create the Async/Event functions. Caveat: I haven't tried this but it was stated in this article. I'll leave confirming this as an exercise for the student J. Included Code: I'm including the complete test project I created to verify the findings. The project was created with VS 2008 SP1. There is a solution file with 3 projects, the 3 projects are: Web Service Asp.Net Application Windows Forms Application To decide which program runs, you right-click a project and select "Set as Startup Project". I created and played with the Windows Forms application to see if it would reveal any secrets. I found that in the Windows Forms application, the generated proxy did NOT include the Begin/Callback functions. Those functions are only generated for Asp.Net pages. Probably for the reasons discussed earlier. Maybe those Microsoft boys and girls know what they are doing. I hope someone finds this useful. Steve Wellens

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  • How can I get a custom made set of checkboxes return values in the postback?

    - by AngryHacker
    I have the following in an aspx page: <td colspan="2"> <% DisplayParties(); %> </td> In the code behind for the aspx page, i have this (e.g. I build HTML for the checkboxes): public void DisplayParties() { var s = new StringBuilder(); s.Append("<input type=\"checkbox\" id=\"attorney\" value=\"12345\"/>"); s.Append("<input type=\"checkbox\" id=\"attorney\" value=\"67890\"/>"); s.Append("<input type=\"checkbox\" id=\"adjuster\" value=\"125\"/>"); Response.WriteLine(s.ToString()); } Not my proudest moment, but whatever. The problem is that when this page posts back via some event on the page, I never get these tags in the Request.Form collection. Is this simply how ASP.NET works (e.g. only server-side control post back) or am I missing something simple. My understanding was that a postback should bring back all the form variables.

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  • How to manage a multiplayer asynchronous environment in a game

    - by Phil
    I'm working on a game where players can setup villages, which can contain defending units. Any of these units (each on their own tiles) can be set to "campaign" which means they are no longer defending but can now be used to attack other villages. And each unit on a tile can have up to a 100 health. So far so good. Oh and it's all asynchronous so even though the server will be aware that your village is being attacked, you won't be until the attack is over. The issue I'm struggling with, is the following situation. Let's say a unit on a tile is being attacked by a player from another village. The other player see's your village and is attacking your units. You don't know this is happening though, so you set your unit to campaign and off you go to attack another village, with the unit which itself is actually being attacked by this other player. The other player stops attacking your village and leaves your unit with say a health of 1, which is then saved to the server. You however have this same unit are attacking another village with it, but now you discover that even though it started off with a 100 health, now mysteriously it only has 1... Solutions? Ideas? Edit The simplest solutions are often the best. I referred to Clash of clans below, well after a bit more digging it seems that in CoC you can only attack players that are offline! ha, that almost solves the problem. I say almost because there's still the situation where a players village could be in the process of being attacked when they come back online, still need to address that. Edit 2 A solution to the "What happens when a player is attacking your village and you come online" issue, could be the attacking player just get's kicked out of the village at that point and just get's whatever they had won up to that point, it's a bit of a fudge but it might work.

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  • Asynchronous Streaming in ASP.NET WebApi

    - by andresv
     Hi everyone, if you use the cool MVC4 WebApi you might encounter yourself in a common situation where you need to return a rather large amount of data (most probably from a database) and you want to accomplish two things: Use streaming so the client fetch the data as needed, and that directly correlates to more fetching in the server side (from our database, for example) without consuming large amounts of memory. Leverage the new MVC4 WebApi and .NET 4.5 async/await asynchronous execution model to free ASP.NET Threadpool threads (if possible).  So, #1 and #2 are not directly related to each other and we could implement our code fulfilling one or the other, or both. The main point about #1 is that we want our method to immediately return to the caller a stream, and that client side stream be represented by a server side stream that gets written (and its related database fetch) only when needed. In this case we would need some form of "state machine" that keeps running in the server and "knows" what is the next thing to fetch into the output stream when the client ask for more content. This technique is generally called a "continuation" and is nothing new in .NET, in fact using an IEnumerable<> interface and the "yield return" keyword does exactly that, so our first impulse might be to write our WebApi method more or less like this:           public IEnumerable<Metadata> Get([FromUri] int accountId)         {             // Execute the command and get a reader             using (var reader = GetMetadataListReader(accountId))             {                 // Read rows asynchronously, put data into buffer and write asynchronously                 while (reader.Read())                 {                     yield return MapRecord(reader);                 }             }         }   While the above method works, unfortunately it doesn't accomplish our objective of returning immediately to the caller, and that's because the MVC WebApi infrastructure doesn't yet recognize our intentions and when it finds an IEnumerable return value, enumerates it before returning to the client its values. To prove my point, I can code a test method that calls this method, for example:        [TestMethod]         public void StreamedDownload()         {             var baseUrl = @"http://localhost:57771/api/metadata/1";             var client = new HttpClient();             var sw = Stopwatch.StartNew();             var stream = client.GetStreamAsync(baseUrl).Result;             sw.Stop();             Debug.WriteLine("Elapsed time Call: {0}ms", sw.ElapsedMilliseconds); } So, I would expect the line "var stream = client.GetStreamAsync(baseUrl).Result" returns immediately without server-side fetching of all data in the database reader, and this didn't happened. To make the behavior more evident, you could insert a wait time (like Thread.Sleep(1000);) inside the "while" loop, and you will see that the client call (GetStreamAsync) is not going to return control after n seconds (being n == number of reader records being fetched).Ok, we know this doesn't work, and the question would be: is there a way to do it?Fortunately, YES!  and is not very difficult although a little more convoluted than our simple IEnumerable return value. Maybe in the future this scenario will be automatically detected and supported in MVC/WebApi.The solution to our needs is to use a very handy class named PushStreamContent and then our method signature needs to change to accommodate this, returning an HttpResponseMessage instead of our previously used IEnumerable<>. The final code will be something like this: public HttpResponseMessage Get([FromUri] int accountId)         {             HttpResponseMessage response = Request.CreateResponse();             // Create push content with a delegate that will get called when it is time to write out              // the response.             response.Content = new PushStreamContent(                 async (outputStream, httpContent, transportContext) =>                 {                     try                     {                         // Execute the command and get a reader                         using (var reader = GetMetadataListReader(accountId))                         {                             // Read rows asynchronously, put data into buffer and write asynchronously                             while (await reader.ReadAsync())                             {                                 var rec = MapRecord(reader);                                 var str = await JsonConvert.SerializeObjectAsync(rec);                                 var buffer = UTF8Encoding.UTF8.GetBytes(str);                                 // Write out data to output stream                                 await outputStream.WriteAsync(buffer, 0, buffer.Length);                             }                         }                     }                     catch(HttpException ex)                     {                         if (ex.ErrorCode == -2147023667) // The remote host closed the connection.                          {                             return;                         }                     }                     finally                     {                         // Close output stream as we are done                         outputStream.Close();                     }                 });             return response;         } As an extra bonus, all involved classes used already support async/await asynchronous execution model, so taking advantage of that was very easy. Please note that the PushStreamContent class receives in its constructor a lambda (specifically an Action) and we decorated our anonymous method with the async keyword (not a very well known technique but quite handy) so we can await over the I/O intensive calls we execute like reading from the database reader, serializing our entity and finally writing to the output stream.  Well, if we execute the test again we will immediately notice that the a line returns immediately and then the rest of the server code is executed only when the client reads through the obtained stream, therefore we get low memory usage and far greater scalability for our beloved application serving big chunks of data.Enjoy!Andrés.        

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  • Wiring up JavaScript handlers after a Partial Postback in ASP.NET

    - by Richard
    I am trying to use LinkButtons with the DefaultButton property of the ASP.NET Panel in an UpdatePanel. I have read and used the various other answers that are around describing the wiring up of the click event so that a full postback is not done instead of a partial postback. When the page loads, I wire up the .click function of the LinkButton so that the DefaultButton property of the ASP.NET panel will work. This all works fine, until you bring an UpdatePanel into the mix. With an UpdatePanel, if there is a partial postback, the script to wire up the .click function is not called in the partial postback, and hitting enter reverts to causing a full submit of the form rather than triggering the LinkButton. How can I cause javascript to be executed after a partial postback to re-wire up the .click function of the LinkButton? I have produced a sample page which shows the problem. There are two alerts showing 1) When the code to hook up the .click function is being called, and 2) When the .click function has been called (this only happens when you hit enter in the textbox after the event has been wired up). To test this code, type something in the textbox and hit Enter. The text will be copied to the label control, but "Wiring up Event Click" alert will not be shown. Add another letter, hit enter again, and you'll get a full postback without the text being copied to the label control (as the LinkButton wasn't called). Because that was a full postback, the Wiring Up Event Click event will be called again, and the form will work properly the next time again. This is being done with ASP.NET 3.5. Test Case Code: <%@ Page Language="C#" Inherits="System.Web.UI.Page" Theme="" EnableTheming="false" AutoEventWireup="true" %> <script runat="server"> void cmdComplete_Click(object sender, EventArgs e) { lblOutput.Text = "Complete Pressed: " + txtInput.Text; } void cmdFirstButton_Click(object sender, EventArgs e) { lblOutput.Text = "First Button Pressed"; } protected override void OnLoad(EventArgs e) { HookupButton(cmdComplete); } void HookupButton(LinkButton button) { // Use the click event of the LinkButton to trigger the postback (this is used by the .click code below) button.OnClientClick = Page.ClientScript.GetPostBackEventReference(button, String.Empty); // Wire up the .click event of the button to call the onclick function, and prevent a form submit string clickString = string.Format(@" alert('Wiring up click event'); document.getElementById('{0}').click = function() {{ alert('Default button pressed'); document.getElementById('{0}').onclick(); }};", button.ClientID, Page.ClientScript.GetPostBackEventReference(button, "")); Page.ClientScript.RegisterStartupScript(button.GetType(), "click_hookup_" + button.ClientID, clickString, true); } </script> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <head> <title>DefaultButton/LinkButton Testing</title> <style type="text/css"> a.Button { line-height: 2em; padding: 5px; border: solid 1px #CCC; background-color: #EEE; } </style> </head> <body> <h1> DefaultButton/LinkButton Testing</h1> <form runat="server"> <asp:ScriptManager runat="server" /> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <div style="position: relative"> <fieldset> <legend>Output</legend> <asp:Label runat="server" ID="lblOutput" /> </fieldset> <asp:Button runat="server" Text="First Button" ID="cmdFirstButton" OnClick="cmdFirstButton_Click" UseSubmitBehavior="false" /> <asp:Panel ID="Panel1" runat="server" DefaultButton="cmdComplete"> <label> Enter Text:</label> <asp:TextBox runat="server" ID="txtInput" /> <asp:LinkButton runat="server" CssClass="Button" ID="cmdComplete" OnClick="cmdComplete_Click" Text="Complete" /> </asp:Panel> </div> </ContentTemplate> </asp:UpdatePanel> <asp:Button runat="server" ID="cmdFullPostback" Text="Full Postback" /> </form> </body> </html>

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  • SQL SERVER – Asynchronous Update and Timestamp – Check if Row Values are Changed Since Last Retrieve

    - by pinaldave
    Here is the question received just this morning. “Pinal, Our application is much different than other application you might have come across. In simple words, I would like to call it Asynchronous Updated Application. We need your quick opinion about one of the situation which we are facing. From business side: We have bidding system (similar to eBay but not exactly) and where multiple parties bid on one item, during the last few minutes of bidding many parties try to bid at the same time with the same price. When they hit submit, we would like to check if the original data which they retrieved is changed or not. If the original data which they have retrieved is the same, we will accept their new proposed price. If original data are changed, they will have to resubmit the data with new price. From technical side: We have a row which we retrieve in our application. Multiple users are retrieving the same row. Some of the users will update the value of the row and submit. However, only the very first user should be allowed to update the row and remaining all the users will have to re-fetch the row and updated it once again. We do not want to lock any record as that will create other problems. Do you have any solution for this kind of situation?” Fantastic Question. I believe there is good chance that we can use timestamp datatype in this kind of application. Before we continue let us see following simple example. USE tempdb GO CREATE TABLE SampleTable (ID INT, Col1 VARCHAR(100), TimeStampCol TIMESTAMP) GO INSERT INTO SampleTable (ID, Col1) VALUES (1, 'FirstVal') GO SELECT ID, Col1, TimeStampCol FROM SampleTable st GO UPDATE SampleTable SET Col1 = 'NextValue' GO SELECT ID, Col1, TimeStampCol FROM SampleTable st GO DROP TABLE SampleTable GO Now let us see the resultset. Here is the simple explanation of the scenario. We created a table with simple column with TIMESTAMP datatype. When we inserted a very first value the timestamp was generated. When we updated any value in that row, the timestamp was updated with the new value. Every single time when we update any value in the row, it will generate new timestamp value. Now let us apply this in an original question’s scenario. In that case multiple users are retrieving the same row. Everybody will have the same now same TimeStamp with them. Before any user update any value they should once again retrieve the timestamp from the table and compare with the timestamp they have with them. If both of the timestamp have the same value – the original row has not been updated and we can safely update the row with the new value. After initial update, now the row will contain a new timestamp. Any subsequent update to the same row should also go to the same process of checking the value of the timestamp they have in their memory. In this case, the timestamp from memory will be different from the timestamp in the row. This indicates that row in the table has changed and new updates should not be allowed. I believe timestamp can be very very useful in this kind of scenario. Is there any better alternative? Please leave a comment with the suggestion and I will post on the blog with due credit. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • What determines which Javascript functions are blocking vs non-blocking?

    - by Sean
    I have been doing web-based Javascript (vanilla JS, jQuery, Backbone, etc.) for a few years now, and recently I've been doing some work with Node.js. It took me a while to get the hang of "non-blocking" programming, but I've now gotten used to using callbacks for IO operations and whatnot. I understand that Javascript is single-threaded by nature. I understand the concept of the Node "event queue". What I DON'T understand is what determines whether an individual javascript operation is "blocking" vs. "non-blocking". How do I know which operations I can depend on to produce an output synchronously for me to use in later code, and which ones I'll need to pass callbacks to so I can process the output after the initial operation has completed? Is there a list of Javascript functions somewhere that are asynchronous/non-blocking, and a list of ones that are synchronous/blocking? What is preventing my Javascript app from being one giant race condition? I know that operations that take a long time, like IO operations in Node and AJAX operations on the web, require them to be asynchronous and therefore use callbacks - but who is determining what qualifies as "a long time"? Is there some sort of trigger within these operations that removes them from the normal "event queue"? If not, what makes them different from simple operations like assigning values to variables or looping through arrays, which it seems we can depend on to finish in a synchronous manner? Perhaps I'm not even thinking of this correctly - hoping someone can set me straight. Thanks!

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  • jQuery: How to fire event when all asynchronous calls return?

    - by Jeremy
    I have a jQuery application that loads data from five asynchronous server calls. I do not want to display any data until all five calls return. (I plan on displaying a Loading message until that happens.) How can I detect when all five calls have returned? I considered having each callback method increment a variable (using jQuery's data() method, perhaps) and then waiting for the value to become 5. (I am not sure yet how I would listen for that event.) I do not think this is a very good solution, however. What would happen if two calls return at the same time? Is there a better way to do this?

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  • How do I fire an asynchronous call in asp classic and ignore the response?

    - by Hexate
    Here's the gist: I have a call I want to make in asp, and I do not care about the response. I just want to fire the call and I do not want the page to wait for the response. According to the documentation, it should look something like this: dim xmlhttp : set xmlhttp = Server.CreateObject("MSXML2.ServerXMLHTTP") xmlhttp.Open "POST", url, true '' setting the 'asynchronous' option to 'true' xmlhttp.setRequestHeader "Content-Type", "application/soap+xml; charset=utf-8" xmlhttp.setRequestHeader "Content-Length", Len(XMLData) xmlhttp.send XMLData This works peachy when calling synchronously, but when I flip the ansynchronous option to 'true', nothing fires. What I can gather from the internet is that users do something like the following: While xmlhttp.readyState <> 4 xmlhttp.waitForResponse 1000 Wend Am I crazy in that this does not really seem like an asynchrous call anymore though if you are waiting for a response? putting the line xmlhttp.waitForResponse 1 right after the send will cause the request to fire, but again, I don't want to wait a second. Any thoughts?

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  • [C#] How to consume web service adheres to the Event-based Asynchronous Pattern?

    - by codemonkie
    I am following the example from http://msdn.microsoft.com/en-us/library/8wy069k1.aspx to consume a web service implemented (by 3rd party) using the Event-based Asynchronous Pattern. However, my program needs to do multiple calls to the DoStuffAsync() hence will get back as many DoStuffCompleted. I chose the overload which takes an extra parameter - Object userState to distinguish them. My first question is: Is it valid to cast a GUID to Object as below, where GUID is used to generate unique taskID? Object userState = Guid.NewGuid(); Secondly, do I need to spawn off a new thread for each DoStuffAsync() call, since I am calling it multiple times? Also, would be nice to have some online examples or tutorials on this subject. (I've been googling for it the whole day and didn't get much back) Many thanks

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  • Flash: How to get a list to be processed synchronous instead of asynchronous?

    - by Quandary
    Question: In Flash I have the below function. Now the problem is SaveFurniture, SavePolygons and SaveComments all save to the same XML file. Now SaveFurniture sends JSON encoded data to a ashx handler, which saves it in the xml on the server. The problem is, because flash sends the data asynchronous, the polygons get sent to the polygonsave ashx handler, but before saving of the furniture has completed, thus access error, write process already in progress... // cSaveData.SaveData(); public static function SaveData():void { trace("cSaveData.SaveData"); //NotifyASPXofNewScale(cGlobals.nPlanScale); SaveFurniture(); SavePolygons(); SaveComments(); } What's the best way to process this list, ONE AFTER ANOTHER ? Making a callback in all of them does make the program flow structure very confusing...

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  • Why does using the Asynchronous Programming Model in .Net not lead to StackOverflow exceptions?

    - by uriDium
    For example, we call BeginReceive and have the callback method that BeginReceive executes when it has completed. If that callback method once again calls BeginReceive in my mind it would be very similar to recursion. How is that this does not cause a stackoverflow exception. Example code from MSDN: private static void Receive(Socket client) { try { // Create the state object. StateObject state = new StateObject(); state.workSocket = client; // Begin receiving the data from the remote device. client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReceiveCallback), state); } catch (Exception e) { Console.WriteLine(e.ToString()); } } private static void ReceiveCallback( IAsyncResult ar ) { try { // Retrieve the state object and the client socket // from the asynchronous state object. StateObject state = (StateObject) ar.AsyncState; Socket client = state.workSocket; // Read data from the remote device. int bytesRead = client.EndReceive(ar); if (bytesRead > 0) { // There might be more data, so store the data received so far. state.sb.Append(Encoding.ASCII.GetString(state.buffer,0,bytesRead)); // Get the rest of the data. client.BeginReceive(state.buffer,0,StateObject.BufferSize,0, new AsyncCallback(ReceiveCallback), state); } else { // All the data has arrived; put it in response. if (state.sb.Length > 1) { response = state.sb.ToString(); } // Signal that all bytes have been received. receiveDone.Set(); } } catch (Exception e) { Console.WriteLine(e.ToString()); } }

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  • Which way is preferred when doing asynchronous WCF calls?

    - by Mikael Svenson
    When invoking a WCF service asynchronous there seems to be two ways it can be done. 1. public void One() { WcfClient client = new WcfClient(); client.BegindoSearch("input", ResultOne, null); } private void ResultOne(IAsyncResult ar) { WcfClient client = new WcfClient(); string data = client.EnddoSearch(ar); } 2. public void Two() { WcfClient client = new WcfClient(); client.doSearchCompleted += TwoCompleted; client.doSearchAsync("input"); } void TwoCompleted(object sender, doSearchCompletedEventArgs e) { string data = e.Result; } And with the new Task<T> class we have an easy third way by wrapping the synchronous operation in a task. 3. public void Three() { WcfClient client = new WcfClient(); var task = Task<string>.Factory.StartNew(() => client.doSearch("input")); string data = task.Result; } They all give you the ability to execute other code while you wait for the result, but I think Task<T> gives better control on what you execute before or after the result is retrieved. Are there any advantages or disadvantages to using one over the other? Or scenarios where one way of doing it is more preferable?

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