Multithreading Accessing A Dataset From Within A Threaded Class Instance?
Nov 1, 2011
I was using the following code within a class and creating an instance of that class from within my main form (Main.vb):Dim count As Integer = Main.DbDataSet.Accounts.CountThis was returning the count of accounts within my database.After changing the code so that I could run this in a background thread to save locking up the program, as more data is processed after this point, the count was returning 0 each time.
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Nov 12, 2010
i have
VariableA as Class1
Variable1 as string
Variable1 = "VariableA"
I want to be able to use Variable1 to get access to VariableA(?).
So i want to able to do something like
VariableA.Property1 = "test"
But like this:
Variable1.Property1 = "test"
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Feb 15, 2011
I recently read about using SynchronizationContext objects to control the execution thread for some code. I have been using a generic subroutine to handle (possibly) cross-thread calls for things like updating UI controls that utilize Invoke. I'm an amateur and have a hard time understanding the pros and cons of any particular approach. I am looking for some insight on which approach might be preferable and why.Update: This question is motivated, in part, by statements such as the following from the MSDN page on Control.InvokeRequired
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Apr 11, 2011
i created a threaded form class that i call when i know an update is going to take a while....it is a simple form with a label and an animated marquee progress control. the code is listed at the bottom....whenever i try to set the message, it says i cant do it with error "{System.InvalidOperationException: Cross-thread operation not valid: Control 'MessageLabel' accessed from a thread other than the thread it was created on." from my form (in my SAVE function, i put the following line:[code]....
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Oct 15, 2010
I have 10 threads each using the same sub to do work. This sub is calling a function to save the results. How are the threads accessing the sub? Is each one getting a fresh copy of the sub to do its thing or are they using the same piece of code and need to wait for each other to finish processing? I don't get any hits when searching for such a specific scenario. I am wondering because it is about using sockets (usually lightweight stuff) to retrieve a resource and the cpu is working at 100% all the time. Still it is very fast, 900 internet queries finish in about 3 minutes.
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Mar 1, 2011
I'm writing a really simple file updater which downloads files off from a website and saves them. The download routine is working well, except that it freezes the project while attempting to connect to the host. Easily solved with threading except now when I try to access other form items such as text boxes, labels, form caption, it says I am not doing it in a safe manner and prompts an interrupt in debug. I did some reading on it and I'm still not sure what to do, I'm very new to vbnet and it is still a little confusing to me.
Error: Cross-thread operation not valid: Control 'Form1' accessed from a thread other than the thread it was created on.
Imports System.Threading
Imports System.Net
Imports System.IO
[code]....
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May 13, 2011
Example:
Two files - TestClass.vb, myForm.vb
TestClass.vb looks as follows:
Imports System.Threading
Public Class TestClass
Private myClassThread As New Thread(AddressOf StartMyClassThread)
[code]....
The result:Application runs, no errors or exceptions.Displayed is the listbox and the Start button.I press the start button and a msgbox says "Not Invoked" as expected and upon clicking OK to that msgbox "Start Button Pressed" is added to the Output listbox control.Immediately following that the msgbox pops up again and says "Not Invoked". I was expecting "Invoked" as a separate thread is trying to use the Output listbox control.Of course this results in the Output.Items.Add being attempted which results in no visible result as the thread is not allowed to directly update the UI control.
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Jan 5, 2011
i have an ASP.NET page which has a numebr of user controls within it. There are 2 user controls which are of interest. I need to display either one of them or neither of them, depending on the record selected previously.
In the user controls I need to set properties of some controls which are in a FormView. So in my user control code-behind I have a number of properties which look something like this:
[Code]...
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Apr 13, 2009
I have a class with a background worker in it that does some tasks on a separate thread. I want to fire some events from the background worker thread to the 'main thread' of the class, so that when using this class your not obliged to go make invoke calls for every event handler your using.I'm at a loss of how to do this though. When having a similar problem in a form of usercontrol I always use Me.Invoke, but this method is not present in a class inheriting system.object.
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Oct 2, 2009
I'm working on a class that has multithreading in it, this class has events that are being raised (raiseevent) in a new created threads within the class, for example:
[Code]...
Now when I load this example application an error is raised up saying that there is a cross thread error (Cross-Thread operation not valid control 'Text1' accessed from a thread other than the thread it was created on.) Now I don't want to handle this error within my form (editing the code in the form) what I want to do is to fix this problem within the class (I guess something with invoke?)
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Apr 7, 2012
I have a class that has the following property that is generated by the methods in the constructor.
Public Class clsLoadTables
Private _ds As New DataSet
Public Property ds() As DataSet
Get
[CODE]........................
My problem is that I do not want to inherit this class, but I have other classes that need to access the ds DataSet property. If at all possible I would like to not use inheritance and not load my datatable more than once in the program.
Here is my failed attempt to access the property inside another class that is not inheriting clsLoadTables:
[CODE].........................
How I can access this dataset that I want to load only once in the program from many classes without using class inheritance or a global module?
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Oct 9, 2011
I have the following defined in my "Form1":So that I can access all my database functions anywhere in the main form (database connection is initialized via the "private sub new()" function in the DatabaseManager class.The works fine for all queries done in form1, however I have many other classes I'd like to be able to access the database from.Does anyone know how to access the initiated class in my example? Since right now it is initiated in the main form, if I try to access any functions inside any ot
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Jun 7, 2012
I want to created a nested class that can only be visible to and instantiated from the parent class.But I also want to be able to use an instance of the nested class through a public variable of the parent class.I tried making the nested class private, or making the nested class' constructor private, but it won't compile.Is it possible to do this in .NET?
[Code]...
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Feb 1, 2012
For a little background, I am trying to make an application 'plug-in' based, more or less.Now, I have a business logic .dll, invoked by the main form, that will run and pull some data and spit out a dataset. I then have various other classes/.dlls that work of this dataset.
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Jan 24, 2012
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]....
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Jan 18, 2011
my proble is the following: I have a class MyClass and another class Modifier, which has a method ModifyMyClass(ByRef mc as MyClass) that receives a MyClass instance as ByRef parameter to modify it. A smell of the code is:
[Code]...
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Jun 4, 2011
Right now I have a Email class that has all the properties of an email to send it, and then a SendEmail function which takes those properties and uses them in the following
Public Function SendEmail()
'Exception handling
Try
[Code]....
The loop goes through each email in the array to process its email, however with the multithreaded function I cannot call
"EmailArray(i).ThreadSendBatchEmail()"
So how do I call an objects method when its on a different thread?
And I'm making it multithreaded so I can easily pause the process, and because the program freezes when the send() function is working, this would resolve that.
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Aug 19, 2009
I have a class in which some of the fields are also classes.I can put values in the "normal" properties, but in the others when o try to assign values it gives the: "Object reference not set to an instance of an object"But the code compiles fine.
dados_Defenicao = New ServiceReference1.draftClaimEntryDefinition
dados_Defenicao.arCode = "123"
dados_Defenicao.claimMarket.warrantyType = "w" - Here it gives the error
How can i fix this ?
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Aug 19, 2009
I have a class in which some of the fields are also classes.
I can put values in the "normal" properties, but in the others when o try to assign values it gives the: "Object reference not set to an instance of an object"
But the code compiles fine.
dados_Defenicao = New ServiceReference1.draftClaimEntryDefinition
dados_Defenicao.arCode = "123"
dados_Defenicao.claimMarket.warrantyType = "w" - Here it gives the error
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May 6, 2010
If you run this code you will see that the 500 PictureBoxes that are added ( this is easier to show than adding pixels as a pixel is only a single point ) fall mainly on the diagonal.With regard the RANDOM class, why should this be like this when the bounds of the instances are? >>
p.Location = New Point(x.Next(0, Me.Width + 1
), y.Next(0, Me.Height + 1 ))
as in this code.>>
[code].....-2138214fdeb4
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May 18, 2010
I've createda vb.net class library where I've defined a number of small classes... nothing complicated, just working with strings, sending emails, etc.In another project, I reference the class library and I'm seemingly able to create an instance ofone of tclasses - intellisense shows me all of the plic properties, methods, etc... all looks perfect. No compile errors at all, nothing b gumdropsand lollipops.When I run the app I'm working on that references the class library, it fails at the point where I'm creating an instance of the class and gives me a vague exception, "System.TypeLoadException".
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Jan 20, 2012
Is there a way to define a class such that there can be only a single instance of that class?
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May 20, 2010
I need to create a new instance of a class that needs a member of the calling class. But i can't pass a reference to the calling class through the constructor.The solution i am looking for is something like this:
Public Class ChildClass
Public Sub New(args)
_MyMember = GetMemberFromCallingClass()
[code]....
I want this to work without having to manually pass any references or variables from the calling class to the new instance of ChildClass.
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Jun 11, 2012
I want to create a class that will "search" for something. Basically I load up the "search item" when the class is created and inside the class is logic to do the "search". The result of this logic will be more "searches" that I want to start. How can I have the logic in the class create another instance of the class itself?
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Feb 11, 2009
I am trying to get a handle on SyncLock and multithreading, but I am having some trouble wrapping my head around exactly how it should be implemented. I have a Public Class Utilities with a many Shared Functions. I want to make sure that each function can only be executed when there are no other concurrent calls to the same function. So If I have 2 functions, A and B in a Public Class Utilities, what is the syntax so that a function "locks" while it is being executed, preventing any subsequent calls until the "locking" thread has completed?
CODE
Public Class Utilities
Public Shared Function A (ByRef i As Integer) As Integer
[CODE].............................
I know I need to wrap the statements of execution in a SyncLock block, but I am unsure of the scope of the parameter used with SyncLock...is it private to the function, class, etc? Can the same object be used to lock both functions if they are independent?
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Aug 2, 2009
this code:
If Not DataSet1.Tables.Contains("Table0") Then
DataSet1.Tables.Add(New DataTable("Table0"))
End If
[code].....
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Apr 27, 2010
vs2010 vb.net QUESTION1 If i do a select and fill a datatable and want to access that data from another class. How can I do that? QUESTION1 example
[Code]...
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May 9, 2010
I am currently trying to write classes so that I can access certain functions from any form within my VB project.
My class is defined thus:-
Public Class testclass
Public Function showmes()
MsgBox("Hello everyone"")
Return 0
End Function
End Class
I have added the class into my form using this at the top in the form:
Imports WindowsApplication1.testclass
Obviously, WindowsApplication1 being the name of my project, testclass being within a VB file, saved with my project.
I have attempted to call the function from the form using this:
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
showmes()
End Sub
However I am getting the error "Reference to a non-shared member requires an object reference." I don't understand why there is a problem, since I have used imports to reference the class.
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Feb 18, 2010
I've currently created the class below. For some reason though I can't access the properties I've created through my xaml style.
Public Class Ribbon : Inherits Button
Private mpopDropdown As Popup
Public Property Dropdown() As Popup
[Code].....
but they don't seem to expose the property either. I've also tagged the property as <Bindable(True)> but that didn't seem to do anything.
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Mar 1, 2010
Any some simple examples of how arrays can be put in a Class Module? The examples should show how the array is used and accessed in a form.
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