How do I delay a vb.net program until a file operation completes?

Question

I have this:

    Dim myTemp As String
    myTemp = System.DateTime.Now().ToString("MMMddyyyy_HHmmss") & ".pdf"

    System.IO.File.Copy(myFile, "c:\" & myTemp)
    Application.DoEvents()
    OpenFile(myTemp)

The problem is that when I call OpenFile, which is just a call to a sub that opens a file, it cannot find the file. This is because it is calling it so quickly that the program doesn't have time to actually create the file before the open takes place.

I thought that DoEvents() would rectify this but it does not. I need to wait until the file is created before I open the file. How can I do that?

Answer 1

System.Threading.Thread.Sleep(1000);

Answer 2

This is a bit hacky, but it should work.

Do Until (System.IO.File.Exists("C:\" & myTemp))
    Threading.Thread.Sleep(1)
Loop

Answer 3

That isn't really what Doevents is used for. It is most frequently used to let the UI message queue clear out (let the UI have some CPU time to refresh). It is slightly more complex than I am describing, but that isn't the point of your question so I will move on.

Try this to make the critical section of your code block:

SyncLock Me
  System.IO.File.Copy(myFile, "c:\" & myTemp)
  Application.DoEvents()
End SyncLock

OpenFile(myTemp)

Answer 4

Ideally you should perform the copy on a separate thread that informs the main GUI thread when it is done so it can then perform the open through an Invoke call.

Answer 5

I don't really know much VB.NET, but isn't Copy a blocking call? Are you sure you're not just trying to open the file from the wrong location (or the unescaped backslash invalidates the path)?

What about this? I've added the drive letter to OpenFile, and escaped the backslash both places.

Dim myTemp As String
myTemp = System.DateTime.Now().ToString("MMMddyyyy_HHmmss") & ".pdf"

System.IO.File.Copy(myFile, "c:\\" & myTemp)
OpenFile("c:\\" & myTemp)

Answer 6

In addition to Tom's answer, isnt it better to put a Application.DoEvents() rather then making the thread sleep?

Answer 7

First, you should not call DoEvents anywhere. For the most part, when it is used, it is a hack to circumvent what should really be an asynchronous operation.

That being said, the Copy method is a synchronous operation. The call to OpenFile will not occur until the call to Copy completes.

That being said when the call to OpenFile occurs, if the file does not exist, it is because you copied it to the wrong place, or because some other process is working on the file in question.

Answer 8

I thinf Synclock is not good for this case

for explaination, MSDN can help me

The SyncLock statement ensures that multiple threads do not execute the same statements at the same time. When the thread reaches the SyncLock block, it evaluates the expression and maintains this exclusivity until it has a lock on the object that is returned by the expression. This prevents an expression from changing values during the running of several threads, which can give unexpected results from your code.

in my opinion, copy is blocking method, so thread waits until copying is done

can`t be problem in another place?

Answer 9

dim SourceFile as string

dim DestinationFile as string

SourceFile ="c:/archivo.txt"

DestinationFile ="c:/destino/archivo.txt"

If System.IO.File.Exists(SourceFile) = True Then System.IO.File.Copy(SourceFile, DestinationFile, True)

'or 'My.Computer.FileSystem.CopyFile(SourceFile, DestinationFile, FileIO.UIOption.AllDialogs, FileIO.UICancelOption.DoNothing)

SourceFile ="" DestinationFile =""

else

MessageBox.Show("the file don't copy!")

end if

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