What is the Invoke syntax to marshall data from a background thread receive callback method to a function on the UI Thread?(Form1).
Public Class Form1
MyDelegate = New DisplayData(AddressOf DisplayData)
Private Sub Form1_Load()
MyDelegate = New DisplayData(AddressOf DisplayData)
[code]....
I am trying to call a method that started on a background thread on the UI thread calling BeginInvoke and passing in a delegate as follows:
Dispatcher.BeginInvoke(Function() UpdateApplicationDataUI())
to call this method:
Private Sub UpdateApplicationDataUI()
...
End Sub
However, I get an error in the call to BeginInvoke (the UpdateApplicationDataUI portion of the delegate is stating "Expression does not produce a value").
Me.Dispatcher.BeginInvoke(Function() New Action(AddressOf UpdateApplicationDataUI))
D is a dictionary whose entry values are of Type T..What I'm attempting to do is have a delegate like "Serializer" below that I can invoke on an instance of T, such as "Entry.Value" below.Please see the "return Entry..." line below for my wishful thinking.[code]
View 2 RepliesA non-UI thread in my prog needs to obtain data from a UI listview control. To prevent cross-thread errors I use the following, but it freezes the prog (probably because the "Else" part is never called).What am I doing wrong?
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How do I dynamically call a function with delegates by passing a string to a background thread in VB.NET?
Currently my code is this
Public Sub invertImageBK(ByVal image As Bitmap)
Dim snxl As System.ComponentModel.BackgroundWorker = createBW()
snxl.RunWorkerAsync(New ImageProperties(image.Clone, "invertImage", Nothing))
[Code].....
I'm trying to figure out if it is possible to instantiate and invoke a delegate by name, rather than explicitly. I think the code below explains it fairly well. I want to accept a function name and then instantiate the delegate based on that. In the example I use a select case, but I want to eliminate that and just use the methodName argument itself.
Private Delegate Sub myDelegate()
Private Sub myDelegate_Implementation1()
'Some code
End Sub
Private Sub myDelegate_Implementation2()
[Code] .....
I understand that .NET is multi-threaded and that is a good thing, but I continually run into issues when I have a background worker for example that is updating some control on my form and I have to do:[code] My question is why is this not built into the framework - surely if I am trying to update a DataGridView it should be intelligent enough to know when the update is from another thread and it could do all the above itself?
View 3 RepliesWe have a UI with a progressbar. I know how to invoke, safely, the control from which it was not created from a thread. there are threads being processed in a threadpool, all of which calls an "agent" (which is a notifier to raise an event back to the UI to then increase the progressbar). an "agent" is set as a property in a State object, which is then passed into a method which will be executed on the ThreadPool. so, I invoke on the UI the method to update the progressbar, but the bar does not seem to update at all (screen frozen) and it takes a very very long time for it to execute. without threading, no problem.
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I'm working with the DevExpress XtraGrid control.I have a routine that goes thru and adds all the controls on the current form dynamically, and launches on a seperate thread the routine for a given control to initialize it to the value that will be displayed to the end-user. Some of the controls are displaying calculated values, and take some time to return their values, so that's why we are doing it on a seperate thread.
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I'm using a similar snippet of code for any control properties that have to be updated, and all work fine. On the above code when the actual Invoke is called, it APPEARS that the thread just ends and never calls the delegate, and doesn't return to finish either.
I have some code in c#
BeginInvoke(new MethodInvoker( delegate() {myAppMethod_Tick(sender, e); }));
Now, When I tried to convert that code to vb.net I have below..
BeginInvoke(New MethodInvoker(Function() Do myAppMethod_Tick(sender, e) End Function))
But it does not compile.. What's problem for it?
Because my c# application works ok without any problem..
I have a few textbox for data display and RS232 communication in my application. After I send characters on RS232, I want text boxes display feedback characters from RS232 receive. So in SerialPort_DataReceived() i was told to use Invoke to display received characters on TextBox1, TexBox2.how to define delegate for TextBox1 and call Invoke()?
View 9 RepliesI'm hacking away at some code which seems to have been started, at least in theory, as an MVVM project in Expression Blend, by my predecessor at this company.
I've got a thread running in the background, which is running some operations on items as they happen. In order to prevent any clashes, I've also got that thread running any operations my users call for.
Once those operations are completed, I'd like to bring up a MessageBox to give a summary of the user-initiated operations, but now that they're running off in their own thread, the finishedProcessing event handler is now running on the background thread instead of the interface thread and it's causing my MessageBoxes to appear non-modally.
Back in the WinForms days, I'd have handled that using InvokeRequired, Invoke and a Delegate. I've read that this has been replaced by something called "Dispatcher", but the ViewModel class I'm using doesn't seem to have a Dispatcher object.
The "thisViewModel" class I'm using inherits a class called "WorkspaceViewModel", which inherits "ViewModelBase", both of which look generated to me...
where I can link up to this "Dispatcher" from here?
I am coming from the C# world to VB.NET and this puzzles me. Why are there 2 ways of doing the same thing? or is there some difference I am not aware of? What is the difference between the following:
Public ReadOnly Property Test(ByVal v as String) As Integer
Get
Return SomeOperationOn(v)
End Get
End Property
And
Public Function Test(ByVal v as String) As Integer
Return SomeOperationOn(v)
End Function
When do you use one as opposed to the other?
I'm running into a strange error and I can't move forward Consider the following code
View 1 RepliesSo, I'm having troubles implementing a separate thread. This is because I have a simple class, and in it I start a new thread. So, as it is not any form, I haven't found any way to make it call the function in the UI Thread.
So, I cannot use the Invoke method. Is there any way to call a function from another thread?
I have a GUI which executes on the GUI-thread. Further I have another thrad which does video processing using DirectShow (this is COM).
- Now I want to execute a function on the same thread as where the videoprocessing is executing. This is initiated by the GUI-thread. Touching the COM-referenced object goes wrong if a execute the function from another thread (I understand that). When a call the function from the same thread everything goes fine. But to do this I have the poll some flag-bits in the mainloop, and that is not a 'pretty' solution...
All discussions on the internet are about how change the GUI from a different thread.
I have tried several things:
1) Invoke the function using a delegate. This doesn't wordt, since the function is executed in the GUI thread. (checked bu ThreadID's)
2) BeginInvoke the function using a delegate. May be .net executes the function in a original thread where the object has been created. This does also not work: .net used random threads (probaby from the threadpool)
3) ISynchronizeInvoke, Threading.SynchronizationContext and some other features seems only to work on the GUI thread only...
The question: Is there a way to Post, Send of Invoke a delegate on the specific thread (for example by a reference to this thread or threadID)
i have a background thread when it is done doing its task it notifies the main thread via a delegate sub it seems if the main thread is "busy" then the background thread hangs waiting for the main thread. if this is normal, which i assume it is my background thread, starts another thread, and this 2nd background thread makes the delegate call is this bad practice?
View 2 RepliesIt seems that there is a glitch in Vb, While having some tasks ( Thread ) queued using Tasks if you try to use Invoke, the thread do not resume when the delegate returns.If BeginInvoke is used, it works but the problem is that it become impossible to execute a delegate synchronously.This does force the use of the AutoResetEvent to control the thread.The problem comes when the thread execute some code in a other classes, using a single AutoResetEvent within many classes just give a very dirty code.
View 1 RepliesI want to find the application thread and invoke something on it ... the problem is i have access to NO OBJECTS on the main thread so calling object.invoke is not an option. This is because I am making a plugin for something and have no access to the existing objects on the main thread .
View 4 RepliesI'm having problems with a program where I've got some multi threaded activities addressing the states of check boxes, which in turn are created by a user definable interface To achieve this I'm using the code below, which works on some occasions and crashes on other occasions when it stops with the following error NullReferenceException was unhandled Object reference not set to an instance of an object.Delegate Sub CBSetCallback(ByVal cb As CheckBox, ByVal value As Boolean)
Private Sub SetCheckBox(ByVal cb As CheckBox, ByVal state As Boolean)
If cb.InvokeRequired Then
Dim d As New CBSetCallback(AddressOf CBset)
Invoke(d, New Object() {cb, state})
[code].....
Disclaimer: I know that Thread.Abort is evil. I'm using it as a last resort since some I/O functions (e.g., File.Exists when used on a non-existing network share) block for a large amout of time and do not allow you to specify a timeout.
Question: Is it possible to Abort (as in Thread.Abort) a worker thread started using Delegate.BeginInvoke or do I have to do the Thread handling myself?
I'm trying to invoke the below but the EventHander is not compatible with the RasConnectionEventArgs from my calling event, how would I invoke SetOverlayIcon and my notification icon on the UI thread?
Public Sub watcher_Connected(ByVal sender As Object, ByVal e As RasConnectionEventArgs)
If InvokeRequired Then
BeginInvoke(New EventHandler(AddressOf OnRegChanged))
[code]....
i got a background worker that has the following code in the do work.... one of the things i want to do is to add rows if theres none available ...but i got an error saying i need to do a safe call thread...i already read about it but im stuck i put control.invoke, but that gives me an error too saying Error 1 Reference to a non-shared member requires an object reference.
[Code]...
I am making use of a serial port in a class. I am raising an event from that class to my form calling the class. Event contains data received... I wish to simply populate a textbox from the raised event.Now I am not specifically creating a seperate thread, but I get the normal crossthreading error when trying to update my textbox on the UI, so my assumption is that the serial port and its internal methods probably creates its own threads...Regardless, I am a bit confused as to how to properly implement an invoke, from my main form, pointing to the thread in the instantiated class...
Dim WithEvents tmpRS232 As New clsRS232
Private Sub but_txt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles but_txt.Click
tmpRS232.Set_com_port("COM8", 38400)
[code]....
I Have a Function on my frmMain Class wich will update my control to something else after an invoke. When i type "?Label1.Text" on the Immediate Window, the text property IS updated, but when i go check the Form, nothing happened. The code is just like this
[Code]...
i got a background worker that has the following code in the do work.... one of the things i want to do is to add rows if theres none available ...but i got an error saying i need to do a safe call thread...i already read about it but im stuck i put control.invoke, but that gives me an error too saying Error1Reference to a non-shared member requires an object reference.what can i do to add rows safely?
vb.net
Private Sub BackgroundWorker2_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker2.DoWork
If DataGridView2.Rows.Item(num).Cells.Item(0).Value = "" Then
Control.Invoke(DataGridView2.Rows.Add(1))
CODE:
Is there anything I need to change about this code to let me insert list items to a listbox on the UI thread?
I have created a class for Socket reads so I can create sockets on command. Due to performing a socket read, the program will freeze waiting for incoming data due to being on a single thread. So I created a separate thread for the reading of the sock and attempt to invoke an event to prevent multi-threading errors.
But I am getting an error when trying to Invoke: "Invoke or BeginInvoke cannot be called on a control until the window handle has been created."
How can I fix this or is there a better way to read a sock without freezing the thread?
Class for Sockets:
Option Explicit On
Option Strict On
Imports System.Text
[CODE]...
Calling form code example:
Private WithEvents Socks As clsSock
Private Sub Sock_Connected(ByVal state As String) Handles Socks.Connected
MsgBox("Connected - " & state)
[CODE]...
Here there's an old question about this code.
xmpp.OnLogin += delegate(object o)
{
xmpp.Send(
[code]....
I have one master page and then content page on the master page and also have one UC on the master page, now i want to filter data from usercontrol on and populate on content page using delegate.
I have achieved this in C# but i am not able to do this in VB.NET
Because in VB.NET i am not able to overload event of the uc.
