<br>I would like to provide the users with the ability to cancel out of a long running process.<br><br>In a simple desktop application, this is somewhat simple -- inside the loop that is causing the lengthy process, add a DoEvents() function which yields control to the Windows environment. This will allow the cmdCancel_Click event to be processed.<br><br>However, in my case, the lenghty process is occurring on a completely different machine (client/server environment). For example, the code looks something like this:<br><br>Set objRemote = CreateObject("RemoteApp.RemoteClass, strServerName)<br>objRemote.PerformLenghtyProcess<br>Set objRemote = Nothing<br><br>Just before the method call, I would like to display a window that will display a "please wait..." type of message with a Cancel button. If the user presses the Cancel button, then I would like to stop the .PerformLenghtyProcess method.<br><br>Is this possible?<br><br>Thanks in advance!
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How to implement a "Cancel" button while a lenghty process is running
- Thread starter VB400
- Start date
You could put a doevents loop just after the call, then check check a variable that you set in the 'Cancel' button event. Then kill the process accordingly. (I'm not sure the api to use to kill the process, but the OLE server might have a Quit method, which would be cleaner). You might also look into the API WaitForSingleObject, inside a doevents loop. <br>--Jim
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- #3
<br>Jim,<br><br>The problem is that once I make a call to the server object (i.e. objRemote.PerformLengthyProcess), control remains at that statement until it is finished. Adding a DoEvents loop after it, did not seem to help as control never got to the loop until the process was actually finished.<br><br>Can you elaborate on the WaitForSingleObject thought -- maybe there is something there!<br><br>Thanks!
You need to establish asyncronous communication between the two components. With your current architecture, you have synchronous communication, which means the function call must complete before control returns to the calling program. <p>nick bulka<br><a href=mailto:nick@bulka.com>nick@bulka.com</a><br><a href= > </a><br>
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- #5
VB400,<br>Below is how the api is used for Shell, which is Asynchronous. I now see your issue though, but I'm not sure how to call the ole server in async mode. I'd have to guess that there is indeed some setting like App.Communication = vbAsychronous... This might be in the registry, but I'm not sure. The bad news may be that the creator of the server object may set this at compile time...I don't know enough about that to speak with any certainty, though. Anyway, heres an example of WaitForSingleObject...<br><br><br>Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long<br>Const SYNCHRONIZE = 1048576<br>Dim ProcessId As Long, ProcessHandle As Long, Ret<br><br>ProcessId = Shell(PgmName , vbNormalFocus)<br>ProcessHandle = OpenProcess(SYNCHRONIZE, True, ProcessId)<br>Do<br> Ret = WaitForSingleObject (ProcessHandle, 100)<br> DoEvents<br> If CancelVar = True Then<br> 'app.quit or Kill the shelled process<br> exit do<br> end if<br>Loop While Ret = 258
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- #7
<br>Thanks Jim,<br><br>I copied this code and added it to my personal arsenal. Although it won't help me in this scenario, I do have use for it in a different application.<br><br>Here's what I've learned so far -- since the lengthy process is happening on a different machine, I cannot control the "stoppage" of the process using DoEvents. However, if I start the remote process in an "Asynchronous" manner then I can put that call in a DoEvents loop (as you described above) which will allow me to "interrupt" with the Cancel button.<br><br>Did I get that right?<br><br>I'm hoping that someone already accomplished this and is itching to tell others about it (-:<br><br>
VB400,<br><br>I thought that this was supported - and would be accomplished by using a call back procedure. JohnK in the DCOM forum would know.<br><br>Mike<br> <p>Mike<br><a href=mailto:Mike_Lacey@Cargill.Com>Mike_Lacey@Cargill.Com</a><br><a href= Cargill's Corporate Web Site</a><br>Please don't send me email questions without posting them in Tek-Tips as well. Better yet -- Post the question in Tek-Tips and send me a note saying "Have a look at so-and-so in the thingy forum would you?"
Mike is right that a callback will do what you want. Components can also generate events. Either soloution will require the server component to be recoded.<br> <p>nick bulka<br><a href=mailto:nick@bulka.com>nick@bulka.com</a><br><a href= > </a><br>
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- #10
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