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POHow to gracefully exit from the middle of a nested subroutine when user cancels?
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  1. POHow to gracefully exit from the middle of a nested subroutine when user cancels?
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    copied!<p>(I'm using VB6 but I imagine this comes up in most other languages.)</p> <p>I've got a GUI button that calls a routine that takes a minute or two to complete. I want impatient users to be able to click on the button a second time to have it gracefully exit out of the routine at any point.</p> <p>I used a static variable to make this work pretty well (see code below), but I'm cleaning up the project and I want to put the For/Next loop into its own function, since it's required in several different places in the project. </p> <p>But doing that would break my static flag embedded in the for/next, so I need to make some changes. Before I do something hare-brained with public (global) variables, I thought I'd ask what other (smarter, perhaps actually CS educated) people have done when faced with this problem.</p> <p>So basically my question is how do I replicate this:</p> <pre><code>Private Sub DoSomething_Click() Static ExitThisSub As Boolean ' Needed for graceful exit If DoSomething.Caption = "Click To Stop Doing Something" Then ExitThisSub = False ' this is the first time we've entered this sub Else ' We've re-entered this routine (user clicked on button to stop it) ExitThisSub = True ' Set this so we'll see it when we exit this re-entry Exit Sub ' End If DoSomething.Caption = "Click To Stop Doing Something" For i = 0 To ReallyBigNumber Call DoingSomethingSomewhatTimeConsuming If ExitThisSub = True Then GoTo ExitThisSubNow DoEvents Next ' The next line was missing from my original example, ' prompting appropriate comments DoSomething.Caption = "Click To Do Something" Exit Sub ExitThisSubNow: ExitThisSub = False ' clear this so we can reenter later DoSomething.Caption = "Click To Do Something" End Sub </code></pre> <p>When I move the for/next loop to its own function?</p> <p>I'm thinking I'll change ExitThisSub to a public variable QuitDoingSoManyLongCalculations that will exit the new for/next sub and then the DoSomething_Click in the same way. </p> <p>But I always feel like an amateur (which I am) when I use global variables - is there a more elegant solution?</p>
 

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