Question

I received some justified critical feedback on my last question (How to gracefully exit from the middle of a nested subroutine when user cancels?) for using the caption of a command button as a state variable. I did it because it’s efficient, serving two or three purposes at once with very little code, but I understand how it could also cause problems, particularly in the slightly sloppy way I originally presented it.

I feel like this deserves its own discussion, so here’s the same idea cleaned up a bit and modified to do it ‘right’ (which basically means defining the strings in a single place so your code won’t start failing because you simply changed the text of a command button). I know my variable and control naming convention is poor (OK, nonexistent), so apologies in advance. But I’d like to stay focused on the caption as state variable discussion.

So here we go:

' Global variables for this form Dim DoTheThingCaption(1) As String Dim UserCancel, FunctionCompleted As Boolean  Private Sub Form_Initialize()   ' Define the possible captions (is there a #define equivalent for strings?)   DoTheThingCaption(0) = 'Click to Start Doing the Thing'   DoTheThingCaption(1) = 'Click to Stop Doing the Thing'    ' Set the caption state when form initializes   DoTheThing.Caption = DoTheThingCaption(0) End Sub  Private Sub DoTheThing_Click() ' Command Button  If DoTheThing.Caption = DoTheThingCaption(0) Then   UserCancel = False ' this is the first time we've entered this sub Else ' We've re-entered this routine (user clicked on button again      ' while this routine was already running), so we want to abort   UserCancel = True ' Set this so we'll see it when we exit this re-entry   DoTheThing.Enabled = False 'Prevent additional clicks   Exit Sub End If  ' Indicate that we're now Doing the Thing and how to cancel DoTheThing.Caption = DoTheThingCaption(1)  For i = 0 To ReallyBigNumber   Call DoSomethingSomewhatTimeConsuming   If UserCancel = True Then Exit For ' Exit For Loop if requested   DoEvents ' Allows program to see GUI events Next  ' We've either finished or been canceled, either way ' we want to change caption back DoTheThing.Caption = DoTheThingCaption(0)  If UserCancel = True Then GoTo Cleanup  'If we get to here we've finished successfully FunctionCompleted = True Exit Sub '******* We exit sub here if we didn't get canceled *******   Cleanup: 'We can only get to here if user canceled before function completed  FunctionCompleted = False UserCancel = False ' clear this so we can reenter later DoTheThing.Enabled = True 'Prevent additional clicks  End Sub  '******* We exit sub here if we did get canceled *******  

So there it is. Is there still anything really that bad about doing it this way? Is it just a style issue? Is there something else that would give me these four things in a more desirable or maintainable way?

1. Instant GUI feedback that user’s button press has resulted in action
2. Instant GUI feedback in the location where user’s eyes already are on how to CANCEL if action is not desired
3. A one-button way for users to start/cancel an operation (reducing the amount of clutter on the GUI)
4. A simple, immediate command button disable to prevent multiple close requests

I can see one concern might be the close coupling (in several ways) between the code and the GUI, so I could see how that could get to be a big problem for large projects (or at least large GUIs). This happens to be a smaller project where there are only 2 or 3 buttons that would receive this sort of ‘treatment’.

Answer 1

I think it’s better to decouple the caption text from the state of processing. Also the goto’s make it hard to read. Here is my refactored version…

Private Const Caption_Start As String = 'Click to Start Doing the Thing' Private Const Caption_Stop As String = 'Click to Stop Doing the Thing'  Private Enum eStates   State_Initialized   State_Running   State_Canceled   State_Completed End Enum  Private Current_State As eStates  Private Sub Form_Initialize()    DoTheThing.Caption = Caption_Start   Current_State = State_Initialized  End Sub  Private Sub DoTheThing_Click()    If Current_State = State_Running Then      'currently running - so set state to canceled, reset caption'     'and disable button until loop can respond to the cancel'     Current_State = State_Canceled     DoTheThing.Caption = Caption_Start     DoTheThing.Enabled = False    Else      'not running - so set state and caption'     Current_State = State_Running     DoTheThing.Caption = Caption_Stop      'do the work'     For i = 0 To ReallyBigNumber       Call DoSomethingSomewhatTimeConsuming        'at intervals check the state for cancel'       If Current_State = State_Canceled Then         're-enable button and bail out of the loop'         DoTheThing.Enabled = True         Exit For       End If        DoEvents      Next      'did we make it to the end without being canceled?'     If Current_State <> State_Canceled Then       Current_State = State_Completed       DoTheThing.Caption = Caption_Start     End If    End If  End Sub