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I am currently in the process of learning the vb.net environment after spending a number of years using VB6.
I took one of my straight forward single threaded apps in VB6 and used the upgrade wizard to convert this app to .net. I've got most of the conversion issues resolved, but I am now getting messages warning about accessing objects from a thread different than the one that created the object. So I'm a bit confused since the original VB6 app - which works fine by the way - had only one thread.
Why am I getting these sorts of messages? I've searched through the code - with my limited exposure to multithreading - and not found anything obvious that I've somehow created a Hydra from a single snake.
My preference would be how to "just make it simple" - a single threaded .net app. All of the references I find to multithreading talk about how to do it. I really - at least at this point - want to know how to avoid it.
I know that soon I will wade in and learn multithreading, but I'd like to do it on my terms.
Any ideas? Pointers to some reference material?
Thanks,
Rick
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simple answer is to remove the
dim myThread as new thread(addressof ThreadCodeSubRoutine)
myThread.Start
and replace it with the call to the ThreadCodeSubRoutine. But .NET introduced thread saftey so you have to invoke a routine to update the controls that are on your form. a bit similar to
Delegate Sub UpdateMyForm(byref SomeValue as string)
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
dim MyThread as new thread(addressof MyThreadCode)
MyThread.start("HI")
End Sub
Private MyThreadCode(byval Message as string)
dim DelegateVariable as new UpdateMyForm(Addressof WriteToLabel)
me.Invoke(DelegateVariable, Message)
End Sub
Private Sub WriteToLabel(byval Message as String)
label1.Text = Message
end sub
But Also have a read of this MSDN Control.Invoke Method (for Threads use)[^]
Lobster Thermidor aux crevettes with a Mornay sauce, served in a Provençale manner with shallots and aubergines, garnished with truffle pate, brandy and a fried egg on top and Spam - Monty Python Spam Sketch
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Ah, but here's the rub... there is no command in the code that invokes a new thread. I searched through the entire project looking for "thread" or "addressof" and found nothing. That's what gotten me perplexed - can't seem to find out how or where the second thread (if there is one) gets created.
The messages mentioning threads are related to updating form objects, so should I assume that the "thread safety" is the culprit here? In other words, even for a simple single threaded application, do I need to create a separate thread to handle form updating?
Rick
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You're going to have to show the code that's throwing up the errors. I've never seen a case where the conversion wizard generates threaded code on its own.
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There are some possibilities to run into multi-threading without directly intending it.
When you communicate with other applications (e.g. an outproc COM server), events can come from other threads.
If you use the application framework for running only one instance of your application, a second start of the application will send the calling parameters to the running application in a different thread.
Use the Invoke/BeginInvoke function to transfer the call into the main thread.
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How to Add 3 columns from database to ComboBox, I want to visible 2 of them I use this
reader = OleDbCommand1.ExecuteReader()
Dim dt = New System.Data.DataTable()
dt.Load(reader)
ComboBox2.DataSource = dt
ComboBox2.DisplayMember = "column1"
ComboBox2.ValueMember = "column3"
ComboBox2.SelectedIndex = -1
reader.Close()
this work
but can I use this
ComboBox2.DisplayMember = "column1" + "column2"
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in a nutshell you have create a custom class from combobox to do it
have a read of this Multiple columns combo box vb.net[^]
Lobster Thermidor aux crevettes with a Mornay sauce, served in a Provençale manner with shallots and aubergines, garnished with truffle pate, brandy and a fried egg on top and Spam - Monty Python Spam Sketch
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I have a VB application I wrote in 2002 with Visual Studio 2002 at that time. It copies files and directories with a variety of parameters. We use the utility to copy files from server to server or destktop to desktop via scheduled tasks, etc.
It is a framework 1.0 app and has worked for years. This past year it was evident it needs upgraded to VS 2010. Everything is working fine except in Windows 7 with parameters we've used for years with XP and on the servers, when we copy a root directory, for example, D:\, the copy program will try to copy the Recycle Bin and the System Volume Information and fail. In previous operating systems I'm guessing it didn't try to copy these items, but in Windows 7 for some reason it does.
We really don't want to copy these two items anyhow, so in the new VS VB 2010 code I wrote the following logic, but I've found that from one server it isn't working:
<br />
Dim source as string = "D:\"<br />
Dim currentDirectory As DirectoryInfo = New DirectoryInfo(source)<br />
Dim di As DirectoryInfo<br />
For Each di In currentDirectory.GetDirectories()<br />
If blnIsRoot = True Then<br />
If (di.Attributes = FileAttributes.Normal) Or _<br />
(di.Attributes = FileAttributes.Directory) Or _<br />
(di.Attributes = FileAttributes.SparseFile) Or _<br />
(di.Attributes = FileAttributes.ReparsePoint) Or _<br />
(di.Attributes = FileAttributes.NotContentIndexed) Or _<br />
(di.Attributes = FileAttributes.System) Or _<br />
(di.Attributes = FileAttributes.Offline) Or _<br />
(di.Attributes = FileAttributes.Temporary) Or _<br />
(di.Attributes = FileAttributes.Device) Or _<br />
(di.Attributes = FileAttributes.Hidden) Or _<br />
(di.Attributes = FileAttributes.Encrypted) Or _<br />
(di.Attributes = FileAttributes.Compressed) Or _<br />
(di.Attributes = FileAttributes.Archive) Or _<br />
(di.Attributes = FileAttributes.ReadOnly) Then<br />
<br />
.... logic to copy directory<br />
<br />
end if statments, next statements, etc...<br />
With this code, it will copy a root directory (d:\) and all sub directories and ignore the recycle bin and system volume information.
Code works 99% of the time, but with one server which houses our intranet, I'm copying from \\inttranetserver\wwwroot\dept\its\ to d:\test\ and it is not copying any directories at all, even though there are multiple under ..\its\
I run the code in debug, set breakpoints and skip the if statement (shown above) checking attributes and it works fine, but put that if statment back in it doesn't copy any of the directories.
I'd like to use better logic, for example something that checks for "if recycle bin or if system volume information" but I haven't found anything.
Any suggestions? 
Thanks
Lost in the vast sea of .NET
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Hi,
some facts:
1. file attributes are flags, several of them can be set at the same time, so your compare statements aren't going to cut it.
2. Windows, since Vista, is more protective about a number of files and folders, your old code is probably getting access violations.
what I do:
- copy everything you need in a big loop; inside the loop, have a try-catch, and log each individual failure.
- before copying, check for some special names and skip those.
- the exceptions will tell you which files you will have to skip, i.e. which checks to add to your code.
- and this will have to amended every time you move to the next Windows version...
Luc Pattyn [My Articles] Nil Volentibus Arduum
Fed up by FireFox memory leaks I switched to Opera and now CP doesn't perform its paste magic, so links will not be offered. Sorry.
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On this fact:
"file attributes are flags, several of them can be set at the same time, so your compare statements aren't going to cut it."
I am seeing this when I follow via breakpoints, where it seems like several attributes are set. This makes sense to me.
Your suggestions:
- copy everything you need in a big loop; inside the loop, have a try-catch, and log each individual failure.
- before copying, check for some special names and skip those.
I like your suggestions, I just have a question. As far as tracking it to a log file, what attributes do you think I should catch that would be helpful to log? di.Attributes, di.fullname... anything else?
When you say special names, are you saying if I check fullname and the name of the recycle bin to a string I define "Recycle Bin ...". Is the name always consistent. We have several differnt servers 2000, 2003, 2008 and workstations are basically XP, Vista, and now 7. I assume the names might change between operating systems and the log will be helpful. I like this idea, but hoping you can clarify a little?
Thanks for your help!
Lost in the vast sea of .NET
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KreativeKai wrote: what attributes ...?
just the name, attributes aren't relevant, they can change, e.g. when a backup is made.
KreativeKai wrote: special names...
check everything you ever encountered, do not change with the Windows version, just add to the skip list:
for (...) {
...
if (shortName=="Recycle Bin") continue;
if (shortName=="Trash Can") continue;
...
try {
....
} catch(...) {
....
}
}
Luc Pattyn [My Articles] Nil Volentibus Arduum
Fed up by FireFox memory leaks I switched to Opera and now CP doesn't perform its paste magic, so links will not be offered. Sorry.
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Thanks for all your help Luc! It is appreciated! 
Below is the code I used in case anyone else can learn from it later when searching the message boards...
<br />
Dim di As DirectoryInfo<br />
For Each di In currentDirectory.GetDirectories()<br />
Dim strDirectoryName As String = di.Name<br />
Dim intFoundRB As Integer = strDirectoryName.IndexOf("$RECYCLE.BIN")<br />
Dim intFoundSV As Integer = strDirectoryName.IndexOf("System Volume Information")<br />
'Skip $Recycle.Bin or System Volume Information directories<br />
If (intFoundRB = -1) And (intFoundSV = -1) Then<br />
Try<br />
... Copy logic<br />
Catch ex As Exception<br />
... logic writing to log file for future reference if needed...<br />
End Try<br />
End If<br />
Next
Lost in the vast sea of .NET
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On top of what Luc said, why are you even checking attributes?? Unless they determine eligibility of a file to be copied, you have no need to look at the file attributes. Your code snippet suggests that you're not using the attributes for anything at all, so I'd just remove the checks.
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Hi Dave,
I was checking attributes because originally I was hoping to exclude the Recycle Bin and System Volume Information by skipping a system attribute, but found through testing that if I did an "if statement" with all the attributes it worked. Didn't make sense, but worked... Unfortunately from our intranet server, the copy was skipping those folders, so the logic was no longer sound.
You would think Microsoft would have a way of catching the recycle bin in the logic by looking for an attribute of some kind related to system files/directories?
Oh well, the logic worked by catching the name of the directories and skipping them that way.
Thanks for the feedback! Always appreciated!
Lost in the vast sea of .NET
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For future reference, your code wasn't checking to see if any attributes were turned on. That IF statement you posted only returned True if one and only one attribute was turned on. Your check got lucky if it returned true.
You would normally check to see if a single bit flag is enabled like this:
If (di.Attributes And FileAttributes.System) = FileAttributes.System Then
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Thanks for the clarification! It is evident now that I was misunderstanding the File.Attributes logic.
Lost in the vast sea of .NET
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download the visual basic 6.0 softwear
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VB 6 is a dead system. If you are interested in developing using Visual Basic then get a copy of the express version[^].
Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman
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Dead system? Feh. "It has worked for ten years, we don't need to upgrade! Now, I need this list of changes implemented by tomorrow...."
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"Good luck in finding 10 year old hardware with a 10 year old OS that still supports your platform. Better yet, try and get tech support from Microsoft, and don't forget to invite me when you try."
Either one moves on, or ones becomes obsoleted.
Bastard Programmer from Hell 
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Visual Basic 6.0 was never free.
However, it would be prudent you look at working in .Net instead of VB6 now.
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Thanks, I won't, I just don't think so.
Luc Pattyn [My Articles] Nil Volentibus Arduum
Fed up by FireFox memory leaks I switched to Opera and now CP doesn't perform its paste magic, so links will not be offered. Sorry.
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Go on, give it a try, you might like it. 
Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman
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