VS 2010 : Multithreading And Accessing Other Routines/form Properties?
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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Feb 4, 2010
Accessing Properties Of Form Classes
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Mar 25, 2010
Is there a way to annotate functions, subs, properties, and methods so that tool tips will pop-up in the IDE as they're being defined or selected?
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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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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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Jun 12, 2012
I have a datagridview on a form and this shows up my list of suppliers. I have a textbox which when i click shows up the supplier list and from there when i double click on a row, the supplier's name is shown in the textbox. The thing is i have to do same on the same page for search purposes which got its own textbox. But the cell double-click event already contains code that will display it in some other textbox like i mentioned previously. What i thought is to make another form with a datagridview. So this datagridview will be used to display the supplier's name in search textbox. But what if i have to access this form several times. Do i have to create several forms everytime?
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Jan 18, 2011
Im quite new to VB.Net so, this is what i have. A simple "console" form. Its just a form with a ListBox in it. To add stuff to the ListBox, i have to open the console, to let other forms know what the ListBox there is.
[Code]...
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Jan 18, 2012
I'm having a strange difficulty. Here is the order of events:User presses button on form1 New Form object is created for from 2 New form object '.show' command is fired Form 2 opens correctly In the Load Event of Form 2, the form attempts to do various things in a try, catch, finally clause On catch, I close form2 down '.close' as it cannot be used as something has gone wrong with the execution However, my problem is this. It is acceptable for things to go wrong on the from 2 load event which is why I have implemented the try - catch functionality. However, when I close the form2 down as a result of the problem, a real error ocurrs 'Cannot access a disposed object' and the VB IDE refers me to Form1's '.show' event for Form2.
It is almost as if the form hasn't fully 'shown' before I am closing it down. Does anyone have any idea what the problem is here? Do I need to close down Form2 ourside of it's Load event handler so that Form1 thinks it has loaded correctly?
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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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Apr 8, 2010
Is it possible for one class to access an array of values within another class as a readonly property of the second class? All of the examples and references on class properties imply that one can only retrieve one value by calling a class' property.
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Sep 26, 2011
I have an exceptionhandler function that basically just writes a line to a textbox on Form1. This works fine when being run normally but the second I use a thread to start a process it cannot access the property. No exception is thrown but no text is written to the textbox:
Public Sub ExceptionHandler(ByVal Description As String, Optional ByVal Message As String = Nothing)
' Add Error To Textbox
If Message = Nothing Then
Form1.txtErrLog.Text += Description & vbCrLf
Log_Error(Description)
[Code] .....
Is it possible to access a form's properties from a thread this way or would it be easier to write to a text file or similar and refresh the textbox properties every 10 seconds or so (Don't see this as a good option but if it's the only way it will have to do!).
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Aug 30, 2009
If I have a custom windows service running on a server, is there anyway I can access the value of a property/variable within that service? For example, I would like to have a client vb program be able to "read" the value some variable from that service. A simple example would be the service would capture a boolean value of the success or failure of the last time it kicked off a process. I would then like to have a client windows app "connect" with the service and be able to read that boolean value.
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Jan 28, 2011
I want to know the correct way to access an object that is stored as an object in another object...phew. Here is what I'm trying to do...
I'm creating a restaurant map and to keep things simple I have 3 classes -- cServer, cTable and cGuest. cTable has a property which should contain a cServer object eg
Public Property Server() As Object
'Called when the property is read
Get
[Code].....
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Feb 2, 2010
I have masterpage.master.vb where I have properties, such as;
Private _SQLerror As String
Public Property SQLerror() As String
Get
[Code]....
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Jul 21, 2011
I'm trying to update a dependancy property in VB.Net 4.0 inside of an Async callback. I feel like I am doing this correctly but I'm still getting the "The calling thread cannot access this object because a different thread owns it." error. Does someone see a better way of using delegates in VB.Net 4.0?
Private WithEvents myObj as CallingObject
Private Delegate Sub MyErrorDel(ByVal strError as string)
Public Property ErrorMessage As String
[code]....
Whenever ErrorMessage gets set inside of DisplayError an exception gets thrown, even though I am using the dispatcher to call DisplayError.
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Jun 10, 2009
I am moving from VB to C#. I am trying to loop through a collection class which is a collection of data classes but I can't seem to get the actual values out of the data class properties(find the correct code to do so). I have a method that loops through the collection class(Contacts) and saves each record(Contact). I am using reflection because my method will not know if it is Contacts class or a Customer class and so forth. Here is my code in VB(watered down)
Public Function SaveCollection(ByVal objCollection as Object, ByVal TableName as string, ByVal spSave as string)
Dim objClass as Object
[Code]....
The C# code keeps returning null. In my locals window I can see the proprties on the class on objClass and the value of the propery but I can seem to figure out how to access it through code. I used the DictionaryBase because that seems to closely match would I need to do. My data class(Contact) has a bunch or properties that match the field names in the database of the Contact Table. After I get the propInfo variable set I then set up my SQLParameter with the fieldname, datatype etc and then set the value to the propInfo.value.
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Nov 1, 2011
I am trying to access MS/Word document properties without opening the file in Word. Right now I have an app that reads the document properties but it has to open the document in word. This makes it run very slowly and also makes it susceptible to crashing if the document is corrupted. In Windows Explorer, you can right-click on a word document file and select properties. The ensuing dialog box contains, in addition to the usual information, two additional tabs labelled "Summary" and "Custom" that correspond to the same tabs in the dialog box you can open from File/Properties menu in Word. I know windows explorer is not opening the document in word because there is no instance of word.exe in task manager and because it has no difficulty in obtaining this information from the file even when it cannot be opened in Word because the document has become corrupted.If anyone could help me figure out how to read custom and built-in document fields (properties) from the file without opening it in Word,
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Jun 22, 2009
I need to migrate from Excel 2003 VBA to Excel 2007 VBA. When Microsoft introduced Excel 2007 it removed many objects from the previous versions and added some new objects. Also it hid some properties of particular objects. These hidden properties can be viewed by going to the object browser, right clicking any object and selecting "Show Hidden Members". My problem is I need to access these hidden properties. Is there any way I can access these properties. I can successfully migrate from Excel 2003 VBa to Excel 2007 VBA with the same functionality?
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May 8, 2011
I have to make a VB project for one of my college Co-Sci classes. However, I am having issues doing what I think is logically possible. Part of our project entails creating a user defined class, then create a form that then instantiates an instance of the object type. After that we are to list the item in a listbox. That is all well and good and works fine.
What I need help with is looping through each object in the listbox, getting some data from the object, then moving to the next.
I have been trying something similar to c++. For example, an object contained in a c++ array can be accessed like this:
array[index].someObjectMethod().
How would someone do something similar to that for objects contained in a VB listbox? I imagine it starts something like this:
myListBox.Items(index).
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Jun 11, 2012
I have used the following code to generate buttons dynamically. I want to know how to code in such a way that if i click one button, there should be some change done to some other button in the same form. Since all the buttons are generated in the loop, i do not know how to call one button elsewhere in the code.
Private Sub random2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim i As Integer
[Code].....
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Apr 6, 2010
how to handle movement of buttons that are made in runtime. What my program does is writes the name of a button that is made in runtime, the left, and top cordinate into a textfile. When the user reopens the program it needs to load the button in the same spot. So far i have a streamreader reading the file in each line. There is a one sentence split by ",". Each of the three components are loaded into an array. how can i call the buttons it i am unsure of the name. Possible answer could include using sender, addhandler.
Private Sub LoadBuildingToolStripMenuItem1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles LoadBuildingToolStripMenuItem1.Click
Dim File As OpenFileDialog = New OpenFileDialog
[Code].....
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Sep 17, 2010
I've removed a few controls from my form, but they're still in the properties. I've looked in the Document Outline, but nothing. How can I remove them (save)?
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Mar 5, 2012
In the form design I set up a TableLayoutPanel, 20x20 cells and in cell (1,1) a PictureBox (called Target) containing the image of a small target. The properties box for Target shows some very promising properties, Column and Row - and if you overwrite the values in the properties box, the PictureBox obligingly shifts to the corresponding cell position in th design. However in VB it is not possible to refer to Me.Target.Row or .Column - neither appears during coding in the menu of properties, and deliberately coding either of them produces an error like
Error 1 'row' is not a member of 'System.Windows.Forms.PictureBox'.
1. Why does the properties box show properties that cannot be altered programmatically?
2. How can my program move Target around in the TableLayoutPanel?
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May 11, 2010
I'm using the WIA Aut. Library [URL] , trying to capture photos from 5 digital cameras (Nikon D90) USB-connected to my pc. Now, I partially achieved my goal, what I do is:
- loop through the attached devices, connecting to every camera;
- fotocamera.ExecuteCommand (WIA.CommandID.wiaCommandTakePicture) ;
- other image processing operations...
Everything works fine but... the workflow is camera1 -> connect -> grab pic. => camera 2 -> connect -> grab pic. => camera 3.....
[Code]...
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Feb 9, 2011
I just put a button and a textbox on a form to try and learn to multi thread, i think i've done it correctly. but it still appears to freeze for a little bit just before it attempts to display the data. i think it's the invoking. Is it normal / have a done something wrong?
[Code]...
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Jun 10, 2011
Sub Main() Try'process i files on their own thread
[Code]...
I'm running into a problem when I stop the debugger, the console window stays open, and I can't kill it via task manager.
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Apr 14, 2010
explain to me why the 1st example gives me an error complaining about cross thread yada yada....but the second doesn't, and works? this is inside a worker thread function
[code...]
I understand the concept of needing delegates and all that jazz when working with multiple threads, but why give me an error if there's no invoke required anyway?
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Nov 5, 2010
I have a form that opens a other form in multi threading but after that it wont close I have tried:
application.exit (Works but closes the whole app)
me.close (nothing happens)
end (nothing happens)
me.hide (nothing happens)
This form is form1 that wont close and opens form3 I every other form works.(7 forms total)
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Feb 6, 2011
I've got some troubles with the socket multithreading, basically the form closes without returning any exception and if I run my application after the compilation it just gives me an error about a yet disposed object (read the code for more information)
I'm quite sure I'm mistaking something in the EndReceive method, anyway that's the resource I've looked into: [URL]..I can't figure out why I should use a state object which contains a socket (or tcpclient etc..) variable instead of some public variables in my current socket class.
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Nov 24, 2010
I am developing a software that catches streaming data. Unfortunately, there is no pattern or sequence on how this data comes in. So what I have initially done is to catch then write to my MS Access DB. Unfortunately, while writing to the DB, I am missing some data that is streaming since writing takes a little bit of time before it goes back to the catching syntax.
I am planning to multithread the DB writing then just call it from my main program. Do guys know any website/tutorial where I can learn the basics for multithreading? I am using Visual Studio 2010. Or if ever, does any one of you have a sample program where I can just learn from?
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