Forms :: Asynchronous Programming Using CallBack
Feb 1, 2010
I have a class with a mthod which does a a time consuming task. I know how to start the method in a separate thread using the Threading.Thread class. What I want to do is use callback so as to have the method report its result to another method when completed. I chose to use the asynchronous Begin/End call pattern.
My thoughts are:
Private Function BeginConnect(ByVal URl As String, ByVal callback As AsyncCallback, ByVal state As Object) As IAsyncResult
'Some Code
[Code].....
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Feb 1, 2010
I have a class with a mthod which does a a time consuming task. I know how to start the method in a separate thread using the Threading.Thread class. What I want to do is use callback so as to have the method report its result to another method when completed. I chose to use the asynchronous Begin/End call pattern.
Private Function BeginConnect(ByVal URl As String, ByVal callback As AsyncCallback, ByVal state As Object) As IAsyncResult
'Some Code
End Function
[code]....
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Aug 17, 2009
I have this code obtaining data from a sensor that is sending a string that contains 4 numbers separated by a tab and terminated by an end of line/ I am trying to use an asynchronous callback to get the data over TCP. That problem is that the callback function is not grabbing the complete string. Sometimes it will, other times it gets half in one retrieve and half in another. I need the callback to hold off until it gets a newline character.
Code:
Public Sub readVaisala()
Dim ip As String = "192.168.1.30"
Dim portNumber As Integer = 23
Dim time As Int32 = Now.Second * 1000 + Now.Millisecond
[code].....
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Feb 12, 2011
I have been trying to figure this our for far too long and I cannot get my head around it. Every example I have seen seems to be far more complex that I need. I have a web service in my project (.asmx). I want to call it very simply from a button on a webpage.
Click
Run service asynchronously
return control back to webpage (web
service running in background)
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Feb 23, 2010
i'm creating an Asynchronous socket programming in vb.net. i've utilised the code from Asynchronous client and server code frtom the following links:m a new user so could post only one link fully)When I try to connect the for more than one client the second client always waits until the first clientcompletes the call. i want the clients to accept calls at the same time
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Feb 2, 2011
I am facing problem in asynchronous socket communication.
1)I wanted to perform connect(from client to server) operation on enter button and send the data whatever client want to send and disconnect from server. And again client should get connect to server whenever client wanted to send data. this is the mechanism.
i.e how to reuse the socket.
2)Again Server should able to send the data to client.
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Feb 12, 2010
I noticed that HttpWebRequest freezes the UI while it's waiting for a web page to be downloaded:
[code]
If someone's done this before, what is a good way to keep the application responsive?
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Mar 23, 2011
Situation: i've created several forms with a datagrid:formwithdatagrid1formwithdatagrid2formwithdatagrid3.... These datagrid can be filled manually or with a selection list. I've written this selection list a a new form (frmSelectionList), witch is called with a SQL instruction, now this selectionlist calls a funtion in formwithdatagrid1 to return the selected value. Question:How can the same selectionform being used for all datagridforms?
[Code]...
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Sep 15, 2009
I know how to InvokeScript so my VB form can call a javascript function in the Webbrowser document, but does anyoe know how to do it the other way round - ie javascript calling a vb function in the containing form? Why do I want to do this? Well I've got a table of telephone conversations. Some conversations are longer than others and they look silly in a grid with fixed row height. So I put them in an html document and display them in the webbrowser control. There's a hyperlink on each subject title, and I'd like the hyperlink to open an 'edit conversation' dialog box in my app.
[Code]...
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Mar 8, 2011
I've been making this project for our Major course in Networking Principles and Programming. Our project is an ATM System but with the use of Socket API. My partner and I chose VB.NET even if we're completely beginners.
We've researched about Socket programming in VB.NET, and we're glad that our Client-Server connection worked out. The problem is, our system contains many forms (Withdraw, Deposit, etc). We've researched the Google about Socket Programming in many Window Forms and unfortunately, we can't find any.
How can we be able to maintain the connection with many forms? Or do we have to create a new connection on every form? Is it better to create only ONE form for the client application perhaps?
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Dec 21, 2010
I am just starting to get back into VB programming, and I'm looking for a more elegant solution to an application I'm developing for a production line.I have a series of labels with manufacturing steps. The background color of the steps needs to change to green as the process steps through. Right now it is working as it should, it just seems a little too much like brute force programming.
Right now I'm using a Select statement to change the color of EACH label. The first portion of the Select statement is below. With this method I have to do this same thing for each case.
[Code]...
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Feb 18, 2009
I have an application that create forms and name it randomically. I would like at certain point, to be able to close one or more forms from the main window application.
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Oct 3, 2011
I have a label on form 1 which show the answer, I want that label answer to appear on Form 2 label or text box. Hw do I go around doing that?
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Jul 29, 2008
I have been working with Visual Basic 6 for over a year and have just recently to move up to .net. I have never had problems viewing picture boxes that were on one form thought another.My old code read something like:frm1.img1=frm3images.treeThis would take the image of the tree from a form that is not viable and place that image in the imagebox.
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Jan 28, 2012
I have recently taken a liking to programming, and have programmed a few games in C#,my friend has asked me to program an application for him to use in his shop. But I have no idea of what language is best suitable?
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Feb 18, 2011
How can I set up an asynchronous web service in asp.net?
I want to call a webservice to post some data to a database, but I don't care if the response failed or succeeded.
I can use .net 2.0 or 3.5 only and it can be in vb or c#.
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Jun 19, 2012
I'm trying to use a .DLL which Callbacks a Function of my project, but I can't get it to work.
Declaration from .h file of .DLL
void DLL_EXPORT SetEntity_CallBack(bool Active, _
void (*Entity_Callback)(int Site, int Application, int ID, _
[Code].....
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Mar 15, 2009
I have a small VB.NET application built using VS 2008 and .NET 3.5.Very simply, there is a timer that kicks off every few seconds to download an XML stream from the web. I look at this stream and manipulate it.The problem I am facing is that the remote web server may not respond in a timely fashion to the following line of
[code]...
How can I implement asynchronous calls so that the my application can behave without locking up?
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Oct 12, 2010
I am writing web services with VB.NET (2.0). The client side will use different technologies such as Java and Siebel. So, if I write asynchronous web services, is it possible for different platforms to consume them? I know it is quite easy with a consumer having .NET platform, but not sure for different platforms. Is it enough for them to have asynchronous ability, or should it be a similar platform?
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Feb 2, 2012
I am using a BackgroundWorker, an OleDBDataReader, a DataGridView to retrieve records asynchronously from an Access database. I call ProgressChanged event from the DoWork event every time I retrieve a record. In ProgressChanged event I add that record to the DataGridView and also update a label. There are about 2000 records to retrieve.I have two problems:Although I'm running an asynchronous operation, the UI remains unresponsive unless I use Thread.Sleep() inside the DoWork event (Why?). Using Sleep() method with an argument of 1 causes the process to run 20 times slower! (Process takes about 1 second if I comment out the 'Threading.Thread.Sleep(1)' line, compared to 20 seconds if I use it.) What can I do to get a responsive UI and a fast background operation (at least not 20 times slower!)?The other problem I am facing is: if I close the form while the asynchronous operation is ongoing, I get this exception (I think in the ProgressChanged event): Exception has been thrown by the target of an invocation. I tried using FormClosing event to end the process but no luck. How to fix this?
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Mar 3, 2011
I have a C++ dll that contains a callback. The callback has one parameter that is passed in and one parameter that is passed out. The parameter that is passed from C++ is a variant. So, we are going from a variant in C++ to an object in VB.NET. The function works. However, It seems that there is a memory leak on the VB.Net side. This must be a Marshaling issue. I have tried to use the MarshalAs Functions, but to no avail.
VB.NET
Declare
Function EnableWriteNotification
Lib
[code]....
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Jan 4, 2011
there is error when i use callback function A callback was made on a garbage collected delegate of type 'skynet1!skynet1.Form1+myCallBack::Invoke'. This may cause application crashes, corruption and data loss. When passing delegates to unmanaged code, they must be kept alive by the managed application until it is guaranteed that they will never be called.
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Aug 8, 2011
I am working on a Twitter application and with the authentication process, Twitter returns Two Tokens with a Callback URL, For example: [URL]. How do I extract each token and put them into separate strings?
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May 12, 2011
I am writing classes in VB.Net (both managed). The main class "A" creates an instance of "B". Class "B" must call a method of Class "A". I need to know two things (syntax, etc...):
1. How does class "A" tell class "B" what method to call?
2. How does class "B" call the method?
The method must pass back an array of Shorts (in this particular example), either as a return value, or as a ByRef argument.I don't want to use an event if I don't have to. The execution is timing critical. (I assume event handling involves a lot of overhead by the operating system, but I may be wrong.)
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Oct 15, 2011
I made a TCP server which communicates with multiple clients at once, but I can't seem to be able to make them stable. When one of the client sends 100 packets to the server, the server receives only a few of them.Here's the client code in PasteBin. It shows how the client connects to the server and then sends 100 messages in a For loop to the server.And here's how the server handles the connection. I couldn't paste the full source as it's hundreds of lines long so let me know if it's missing any mandatory parts and I'll upload them as well.
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Jan 9, 2010
I create an automatic ftp file downloader by using FTPwebrequest. In which, is there any possible to download multiple files simultaneously using Asynchrounous and threading concept?
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Jan 24, 2011
I'm using asynchronous to send/receive from a website I want to block the BeginGetRequestStream method which I have done, using
Code:
WaitEvent.WaitOne(1000 * 20, false);
the problem is that it blocks the UI, which I thought it did not so it basically works like GetRequestStream which does block the UI.
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Jun 3, 2011
I basically have a few thousand transactions 7,000 - 10,000 transactions to process over a short time. The flow goes like this.
---> ----> ---> ---> receive (1000) as each transaction takes approx 2 seconds so if i were to process synchronously it would take all night......
Now first i would like to ask if i am going about this the right way ? the service i am communicating with is not .net but is built to handle large amounts of requests. I have obtained the following code that suggests it will do what i am after
dim strxmlreq as string = '(this is where i input my xml string)
Dim request As HttpWebRequest
' Create the request
[CODE]...
The problem i have is if the above will work for me where exactly do i catch the returned xml string ? I assumed "result" would be the xml output string.
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Jun 9, 2011
Download file asynchronous using sockets
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Jul 12, 2011
The scenario is that an ASP.NET webforms page will call a web service in an async manner to make about 8 web service calls to various providers for data. I would like to run them in parallel to speed things up. I also need to wait for them all to come back before moving on.
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