Is there a way to optimize nested if clauses? - vba

Question

for a while now I've tried to solve the decreased speed issue in my Access application when opening a print preview of certain reports. I've noticed that the slow reports have one thing in common - long, nested if clauses. I tried to search the internet for an answer for this issue, but some of the solutions do not apply to Access VBA or they just aren't possible to implement in the case of my application.
I was wondering if there are some commonly known ways that are used in order to avoid if clause monsters?
EDIT: A snip of code - it mostly handles the structure of the report based on certain conditions.
If (strCcDocNumber <> vbNullString) Then
Dim strUpperPart As String, strLowerPart As String
IDModule.placeIDStringsToPrivateVariables strCcDocNumber, ", "
strUpperPart = IDModule.returnUpper()
strLowerPart = IDModule.returnLower()
txtIDs = strUpperPart & vbCrLf & strLowerPart
Else
txtIDs = " " & vbCrLf & " "
End If
If (strOrderNumber = IO_OrderNumber.OrderNumberCode & "12345") Then
txtIDs = txtIDs
txtIDSpec1 = ModuleIDSpec1.getIDSpec1
txtIDSpec2 = ModuleIDSpec2.getIDSpec2
txtIDSpec1.Height = 330
txtIDSpec2.Height = 330
txtUpperLower = "- Ex" & vbCrLf & "- Ex2" & vbCrLf & vbCrLf & "- Ex3"
On Error Resume Next
For Each c In Me.Controls
If (c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1Table") Then c.Height = 0
If (c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1Table") Then c.Visible = False
If (c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1TableExtra") Then c.Height = 0
If (c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1TableExtra") Then c.Visible = False
If (c.Tag = "IDSpec2Texts" Or c.Tag = "IDSpec1Texts") Then c.Visible = True
If (c.Tag = "IDSpec2Texts" Or c.Tag = "IDSpec1Texts") Then c.Height = 330
If (c.Tag = "IDSpec2Texts" Or c.Tag = "IDSpec1TextsExtra" And ModuleTarget.TargetGroup <> "23C") Then c.Visible = True
If (c.Tag = "IDSpec2Texts" Or c.Tag = "IDSpec1TextsExtra" And ModuleTarget.TargetGroup <> "23C") Then c.Height = 330
'+ many more tags
Next
On Error GoTo 0
txtIDSpec1.Visible = True
txtIDSpec2.Visible = True
If (txtIDSpec1 = vbNullString And txtIDSpec2 = vbNullString) Then
txtIDSpec1.Height = 0
txtIDSpec2.Height = 0
txtIDSpec1.Visible = False
txtIDSpec2.Visible = False
End If
Else
'+a lot more similar conditions
EDIT: I remembered which if statements were the most troublesome ones. I think you can't change these ones into select cases or ElseIf statements, because all of the conditions need to be checked...
It goes like this:
If (condition) Then
Do this
If (differentCondition) Then
Do this also
If (completelyDifferentCondition) Then
Do this as well
Else
Do this instead
End If
End If
Else
If (yetAnotherCondition) Then
Do this
Else
Do this instead
End If
End If

Answer 1

I was wondering if there are some commonly known ways that are used in
order to avoid if clause monsters?
First step is to work out what you want to achieve, not how you want to do it. In this context, you want to set height and visibility. From here, you can work out what conditions are required to set this.
When you first do this, you will have some monster clauses - but this is OK because you have not clarified your thinking. Work from an assumption of one state unless proven otherwise. Here is an example:
c.visible = True
If ((c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1Table") OR (c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1TableExtra")) then c.visible = True
Of course, the second line can now be simplified a little bit.
If (c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1Table" Or c.Tag = "IDSpec1TableExtra") then c.visible = True
I also I set marker Booleans - for example:
IsSpecTable = (c.Tag = "IDSpec2Table" Or c.Tag = "IDSpec1Table")
IsMySpecialFriend = (c.Tag = "IDSpec1TextsExtra" And ModuleTarget.TargetGroup <> "23C")
[...]
c.Visible = IsSpecTable Or IsMySpecialFriend
These are a couple of techniques I use to simplify complex business logic. I am also looking at the use of flags, but this means converting the text Tag to an enumerated value (I am doing this in VB.Net). This technique, though, simplifies the expression down to a simple mask with a And or Or operator as appropriate.

Answer 2

Consider using Select Case Statements when you have multiple If Statement based off the same value.
MSDN - Select Case Statement
Executes one of several groups of statements, depending on the value of an expression.
For Each c In Me.Controls
Select Case c.Tag
Case "IDSpec2Table", "IDSpec1Table", "IDSpec1TableExtra"
c.Height = 0
c.Visible = False
Case "IDSpec2Texts", "IDSpec1Texts"
c.Visible = True
c.Height = 330
Case "IDSpec1TextsExtra"
If ModuleTarget.TargetGroup <> "23C" Then
c.Visible = True
c.Height = 330
End If
End Select
Next
Performance: Select Case vs If vs If ElseIf
I mentioned in a comment that using a Select Case is more for readability than performance. Which is correct if we are comparing Select Case and If ElseIf statements (read Which way is faster? If elseif or select case).
Select Case and If ElseIf can be considerably faster than multiple If statements. This is because the VBA evaluates every condition in an If statement and will stop evaluating when one condition is meet in the Select Case statement. Note: not all languages do.
Consider this simple test.
Sub Test()
Debug.Print "Test:If Statement Test:"
If ret(1) = 1 Or ret(2) = 2 Or ret(3) = 3 Or ret(4) = 4 Or ret(5) = 5 Then
End If
Debug.Print vbNewLine; "Test:If ElseIf Statement"
If ret(1) = 1 Or ret(2) = 2 Then
ElseIf ret(3) = 3 Then
ElseIf ret(4) = 4 Then
ElseIf ret(5) = 5 Then
End If
Debug.Print vbNewLine; "Test:Select Case Statement"
Select Case 1
Case ret(1), ret(2)
Case ret(3)
Case ret(4)
Case ret(5)
End Select
End Sub
Function ret(n As Long) As Long
ret = n
Debug.Print n,
End Function
Notice that the If statement had to perform 5 operations even though they were all true. The ElseIf had to perform 2 operations because the first 2 operations were grouped in a single If clause. The Select Case only performed a single operation, even though, two operations were grouped together. This is because the Select Case will always stop evaluating conditions when a single condition is true.