second 'If' can come only after the first statement so there will not be run time error- due to the fact that "el_rule" can be sometimes nothing..
so i can't put both in same statement with AND.
but after both 'if statement' i want same lines of code will run if one of the if statement will not happens(else)... is my only option is too just write it twice?
like on following code? thanks for any help!
If el_rule.Length > 0 Then
If LCase(ActiveCell.Offset(0, el_rule.Item(0).Attributes.getNamedItem("column_number").Text).Value) = LCase(el_rule.Item(0).Attributes.getNamedItem("value").Text) Then
Set el = xDoc.SelectNodes("/simulator")
Else
Set el =....... -code first time
End If
else
Set el =....... -code second time
End If
you could use a helper Boolean variable
Dim doIt As Boolean
If el_rule.Length > 0 Then doIt = LCase(ActiveCell.Offset(0, el_rule.item(0).Attributes.getNamedItem("column_number").Text).Value) = LCase(el_rule.item(0).Attributes.getNamedItem("value").Text)
If doIt Then
Set el = xDoc.SelectNodes("/simulator")
Else
Set el =....... -code only time
End If
I don't quite follow (since I don't know what el_rule is), but VBA doesn't have short-circuiting of its Boolean operators such as And. As a consequence, nested If statements are more common in VBA than in other languages. If el_rule is sometimes nothing then you would need to have code like:
If Not el_rule Is Nothing Then
If el_rule.Length > 0 Then
'Code in which el_rule is something And with Length > 0
End If
Else
'code to handle the case when el_rule is nothing
End If
As an alternative, if it is genuinely an exceptional situation for el_rule to be nothing, you could simply write code that assumes it isn't and use error handling to catch the times when it is.
Related
I am curious if Exit Sub, Exit Function, among others should be avoided when coding? I have read in various places that it is a bad practice and that you should, if possible, avoid it.
I have provided a function below to demonstrate what I mean:
Function Test()
Dim X As Integer
X = 5
If X = 10 Then
Test = True
Exit Function
Else
Test = False
Exit Function
End If
End Function
In the case above, the Exit Function isn't necessary since the entire code will be able to finish the entire routine without an issue. But by adding it, will it cause some issues?
The style you're using is from the VB5 and VBA era, which didn't support Return statement and we needed to assign the return value directly to the function name. In VB.NET you should always use Return assignment. Return will do both the assignment and the exit call in one statement.
Regarding your particular example, my impression is that the Exit Function statement does nothing more than doing a GoTo to the nearest End Function line. So these statements in your case are redundant and might get striped off by the compiler (not sure about this one).
Note that Exit statements become a nightmare from code-readability point of view. I have recently been a victim of this particular problem. Visual Basic is such a verbose language and Exit statements go unnoticed by the reader. A structured If/Else block is FAR more readable.
This depends on the current context of your code. If you are within a block (be that a loop, Sub or function etc.) and are attempting to leave, the Exit Statement will do fine.
The Return Statement will also work the same as a Exit Function or Exit Sub, see the answer to this SO question. But personally I prefer the exit statement in a function when I wish to return control to the calling code, but have no value to return.
In practically every case, there's a "better" approach than using Exit Function.
The following example will give the same result, but is shorter, and in my opinion much clearer.
Function Test() As Boolean
Dim X As Integer
X = 5
Return (X = 10)
End Function
To clarify a little, as #dotNET said. This is pre .net code. In dot net, you would change your code slightly to
Function Test() As Boolean
Dim X As Integer
X = 5
If X = 10 Then
Return True
Else
Return False
End If
End Function
This defines test as a function that returns a Boolean result and you use the Return statement to err.. return the result back to the calling statement and exits the function immediately at the aforementioned Return statement
for example ..
Dim result As Boolean
result = test
I would like to know if there is an equivalent of Python's pass statement in VBA.
I am using Excel 2016.
The use of Stop (see this answer) seems to be the best thing to do if you are looking for some "non-statement" that you can use to insert a breakpoint, because the Stop command causes the code to break when it is reached, i.e. you don't even need to mark it as a breakpoint because it is one.
You might also like to consider using Debug.Assert some_logical_expression, which will break automatically whenever the logical expression evaluates to False. So Debug.Assert False would be equivalent to Stop, and Debug.Assert x = 3 would be equivalent to If x <> 3 Then Stop.
In Python you need the Pass, because otherwise the methods will not run.
In VBA, its perfectly ok if you leave an empty method like this:
Public Function Foo() As String()
End Function
Maby you are looking for the "Stop" statement.
The good thing about it is that it doesn't clear your variables.
It depends what are you trying to achieve.
You may declare a Label and then use GoTo Label e.g. declare a label (like Skip:)in your code where you want to jump if a condition is met and then use GoTo Skip
Below is the small demo code to give you an idea about this...
Dim i As Long
For i = 1 To 10
If i = 5 Then GoTo Skip
MsgBox i
Next i
Skip:
I have a piece of vb.net code that I wrote. It's a for loop with two embedded if statements, and the compiler is telling me that each elseif and endif must be preceded by a matching if.
This is my second day of working with vb.net ever, and the only programming experience I have is writing .bat files, so this could be something really stupid. But I cannot figure out why I'm getting these errors, and if you all would be willing to help me out, I would greatly appreciate it!
For Each computer In compArray
If compArray(I) <> Computers.GetKey(I) Then notpresentList.Add(Computers.GetKey(I))
Else
If Computers.GetByIndex(I) = 0 Then disabledList.Add(Computers.GetKey(I))
Elseif Computers.GetByIndex(I)=1 Then enabledList.Add(Computers.GetKey(I))
Elseif Computers.GetByIndex(I)=2 Then unknownList.Add(Computers.GetKey(I))
End if
End if
I += 1
Next
The context for this: I am trying to write a piece of code that will confirm the presence of bitlocker. I wrote in VBScript something that will check whether bitlocker is enabled and then send an email. This piece of code is a part of a program which would retrieve those emails, compare them to a list of computers, and then produce a digest email which states which computers are absent, have bitlocker enabled, disabled, or in an unknown state.
I'm sure there's another and better way to do this, but as I said, I'm fairly new at this, and we need to have this done for legal reasons.
Thanks again!
EDIT: If you need more info, please ask me!
I would use the inline syntax in VB.NETonly with short and simple conditions. Otherwise it makes the code less readable and more error-prone.
Try this:
For Each computer In compArray
If compArray(i) <> Computers.GetKey(i) Then
notpresentList.Add(Computers.GetKey(i))
Else
Dim comp = Computers.GetByIndex(i)
If comp = 0 Then
disabledList.Add(Computers.GetKey(i))
ElseIf comp = 1 Then
enabledList.Add(Computers.GetKey(i))
ElseIf comp = 2 Then
unknownList.Add(Computers.GetKey(i))
Else ' added this to show you that this case is not covered yet
Throw New NotSupportedException
End If
End If
i += 1
Next
Your If…Then lines need to be broken up. Move everything after Then to the next lines and you should be good.
If compArray(I) <> Computers.GetKey(I) Then notpresentList.Add(Computers.GetKey(I))
If…Then statements on one line are self-contained, are not followed with a terminating End If, and may not use ElseIf.
Your confusion is in the VB.NET syntax for If statements. VB.NET allows two different formats which each have different syntax rules: Single-line If statements, and Multi-line If blocks.
A single-line If statement looks like this (notice that there is no End If):
If x Then y = 1
A multi-line If block looks like this:
If x Then
y = 1
End If
When you put code on the same line, after the Then, it assumes that you intend it to be a single-line If statement. Single-line If statements cannot include ElseIf, nor Else conditions. They can only be used for simple conditions. Therefore, to make your code work properly, you need to format it as a multi-line If block by putting the conditional code on the following line, like this:
For Each computer In compArray
If compArray(I) <> Computers.GetKey(I) Then
notpresentList.Add(Computers.GetKey(I))
Else
If Computers.GetByIndex(I) = 0 Then
disabledList.Add(Computers.GetKey(I))
Elseif Computers.GetByIndex(I)=1 Then
enabledList.Add(Computers.GetKey(I))
Elseif Computers.GetByIndex(I)=2 Then
unknownList.Add(Computers.GetKey(I))
End if
End if
I += 1
Next
For more information on the syntax, take a look at the MSDN page on the If statement.
Single line If's should all start with just If:
i.e.
If Computers.GetByIndex(I) = 0 Then disabledList.Add(Computers.GetKey(I))
If Computers.GetByIndex(I) = 1 Then enabledList.Add(Computers.GetKey(I))
If Computers.GetByIndex(I) = 2 Then unknownList.Add(Computers.GetKey(I))
You can also use Select Case to make it more readable, i.e.
Select Case Computers.GetByIndex(I)
Case 0
disabledList.Add(Computers.GetKey(I))
Case 1
enabledList.Add(Computers.GetKey(I))
Case 2
unknownList.Add(Computers.GetKey(I))
Case Else
' Some sort of default action can go here, useful for error catching/prevention
End Select
Something we can just put break point on while making sure it doesn't do anything else.
In c, that would be while(false);
What to do in vb.net?
If you always need it to break there you can put
Stop or Debugger.Break()
If you really want a No-Op for some reason (could this turn into a contest for the most ineffectual single line of code?!), how about these?
System.Threading.Thread.Sleep(1) - 1ms is unlikely to have a huge impact outside of a loop
Debug.Write("") - doesn't appear to output anything.
There is a legitimate use-case for this.
When a temporary breakpoint is required after the statement of interest and this is the last line inside an if statement, an extra no-op type statement is required to place the temporary breakpoint on.
In this case I use:
If someCondition >0 Then
doSomething
Space (1) 'Dummy line to place breakpoint
End If
This returns a string containing one space, but does not assign it to anything. I use it in VBA, but it's also supported in .net
My two cents...
You can combine any series of commands onto one line with colons:
If False Then : End If
Select Case False : Case Else : End Select
I've also made it into a sub. Then it gets a recognizable name of own:
'Definition...
Public Sub noop () 'Or Private, Protected, etc.
End Sub
'Usage...
Sub Main()
If sometest Then
noop
Else
MsgBox "test is false"
End If
End Sub
Very strange question, you could place a BreakPoint about anywhere in the code. But here are some useless lines :
Do While False
Loop
While False
End While
Even the following :
Dim hello = Nothing
Or this :
Format("", "")
A no-op statement is also useful as an aid to document code nicely and make it more easily understandable. You could for example put in a statement like A = A.
For example:
If MyNumber => 100 then A = A
Else:
I know this is an old query, but for what it is worth, my preferred solution to the original question is
Debug.Assert (vbTrue)
If you wanted, you could use a variable instead of vbTrue and then enable/disable all breakpoints in your code by changing one variable
Dim bDisableBreakpoints as Boolean: bDisableBreakpoints = vbTrue
'your code here
Debug.Assert (bDisableBreakpoints)
'rest of your code
Simply change bDisableBreakpoints to vbFalse and the breakpoints will be set wherever you have used Debug.Assert
My personal favorite is
dim b=1
Then I put a breakpoint there.
For a custom object, I want to test two conditions. The first is whether the object is nothing. If so, enter the block. If the object is not nothing, I want to do a test on one of the object's properties, and only enter the block if it passes this test.
So the statement would by akin to:
If myObject Is Nothing Or myObject.myInt > x Then
'Perform my task
End If
If myObject is in fact nothing, this throws an error, since when it tests the second condition, it tries to access a property of an object that isn't there.
Most languages I've worked with in the past would not bother to test the second condition of an Or statement if it found the first condition to be true, so you could get away with writing the line above. VBA doesn't seem to allow this. Is there any equivalent way i could write this statement, without resorting to:
If myObject Is Nothing Then
'Perform my task
ElseIf myObject.myInt > x Then
'Perform my task
End If
?
EDITED FOR CLARITY
You could create a flag:
PerformTheTask = False
If myObject Is Nothing Then
PerformTheTask = True
ElseIf myObject.myInt > x Then
PerformTheTask = True
End If
If PerformTheTask Then
'Perform my task
End If
It doesn't help you resolve your code issue, but I thought I'd include a pointer to the Wikipedia page on short-circuit operator evaluation:
http://en.wikipedia.org/wiki/Short-circuit_evaluation
It includes a useful table of common operators in common languages, classifying whether they abide by short-circuit semantics or always evaluate eagerly. In the specific base of VBA, they confirm that the operands to And and Or are indeed eagerly evaluated.
While it's a little unusual, you could also do the following:
Select Case True
Case myObject Is Nothing, myObject.myInt > x
'Perform task
End Select
Select implicit comparisons will use short-circuit evaluation. "Or" won't.