I am modifying a legacy project that must run in VB6, and I have OOP experience but not VB.
Anyway I thought this would be straightforward, I need to add data to a hashmap.
I can call the retreive data function but not the set data function.
Here is the set data function (or sub I guess).
Sub SetSetting(Name As String, Value)
Member of MBCSettings.MBCSettings
Store the named setting in the current settings map
So if I try to set something like this:
gobjMBCSettings.SetSetting("UserName", "223")
I get: Compiler Error, Expected "="
Is my object broken or am I missing something obvious? Thanks.
Ah VB6... yes.
In order to invoke a method the standard way you do not use parentheses:
gobjMBCSettings.SetSetting "UserName", "223"
If you want to use parentheses, tack in the call command:
Call gobjMBCSettings.SetSetting("UserName", "223")
It should be noted that using parentheses around ByRef argument without the Call keyword, the argument will be sent in as ByVal.
Public Sub MySub(ByRef foo As String)
foo = "some text"
End Sub
Dim bar As String
bar = "myText"
MySub(bar)
' bar is "myText"
Call MySub(bar)
' bar is "some text"
It only complained because you were passing in multiple parameters wrapped with a single set of parentheses. Using () to force ByVal also works in VB.NET.
Related
I have some user-defined types and a function for each that takes those types and does something to them.
The thing is though, I'd like to write one, generic function that takes any of those types, and then just uses TypeName to figure out which one it is, and treats it like it needs to.
How do I do this? I tried taking the parameter as Function Foo(Param As Object), but then it fails when I try to pass in a user-defined type into the function.
User Defined Types (UDT) are not classes (they are similar to Structures in C or Records in Pascal), therefore instances of an UDT are not objects - that's the reason you can not use them as an argument to your function foo.
VBA has a universal data type Variant. So when you have Function Foo(Param As Variant), you can pass anything to the function, Foo 3 or Foo ActiveSheet or Foo "Hello world". Anything, except a UDT... If you try so, you will get a compiler error stating "Only user defined types defined in public object modules can be coerced to or from a variant or passed to late-bound functions.":
Public Type tMyType
i As Integer
s As String
End Type
Sub Test
Dim bar as tMyType
' Compiler complains
foo bar
Dim myUniversalVariant as Variant
' Compiler complains also
myUniversalVariant = bar
End Sub
The official documentation of Variant states that "Variant types now support user-defined types.", however at least on Excel 2016 this is not working (or at least I was not able to do so).
Your best bet is to use Classes. If you're lazy, just create a class module (per Type) and put all members of the type as public members, nothing more needed (I will not start to describe the pros and cons of getter and setter). You just need to remember that now you have to use the New statement to create and Set to assign an instance.
In class module (I named it clsMyType):
public i As Integer
public s As String
In the regular module:
Sub Test
Dim bar as clsMyType
Set bar = new clsMyType
foo bar
Dim myUniversalVariant as Variant
Set myUniversalVariant = bar
foo myUniversalVariant
End Sub
Now depending if your function wants to receive only object or also other stuff (like integers or strings), parameter type can be Variant or Object
Function foo(Param as Object)
Debug.Print TypeName(Param)
End Function
I'm using Access VBA, and I keep getting
Compile error: Argument not optional
whenever I try to pass a collection into a function. What is going on?
Private Sub btnTest_Click()
Dim GarbageLanguages As New Collection
GarbageLanguages.Add "VBA"
PrintCollectionCount (GarbageLanguages) '<-- error happens here
End Sub
Public Sub PrintCollectionCount(c As Collection)
Debug.Print c.Count
End Sub
Short Answer
Remove the parentheses from the following line:
PrintCollectionCount (GarbageLanguages)
Long Answer
For better or worse (mostly worse), VBA has both functions and subroutines:
Function - expression that must return a value
Subroutine - statement that cannot return a value
Unfortunately, using each of them requires slightly different syntax. Suprisingly, this is not a valid subroutine call:
Subroutine(arguments)
Instead, you need to use one of these two options:
Call Subroutine(arguments)
Subroutine arguments
It's even more unfortunate that when you use the wrong syntax, all you get is extremely cryptic error messages. Finally, it's also hard to get used to not using parenthesis because single arguments that are primitive types instead of objects actually work fine:
Subroutine(SomeString) ' works
Subroutine(SomeInteger) ' works
Subroutine(SomeObject) ' does not work
Subroutine(SomeString, SomeInteger) ' does not work
Aside from memorizing the awful error messages, you can try to train yourself to look out for whenever a space gets automatically inserted after the subroutine's name. This:
Subroutine(argument)
gets changed to this:
Subroutine (argument) '<-- RED FLAG
This question already has an answer here:
Array argument must be ByRef
(1 answer)
Closed 6 years ago.
Given the following code:
I can not seem to successfully pass a Range Object Variable from one sub-function to another. I spent an entire day researching, and experimenting before I swallowed pride and came here.
Please read the comments below, and reply with any ideas you have regarding why the LAST two lines will not behave.
Public Sub doSomethingToRows(ROI As Range)
*'do Something with the cell values within the supplied range*
End Sub
'
Public Sub testDoAltRows()
Dim RegionOfInterest As Range 'is this an object or not?
'*The following yields: Class doesn't support Automation (Error 430)*
'*Set RegionOfInterest = New Worksheet 'this just gives an error*
Set RegionOfInterest = Worksheets("Sheet1").Range("A1")
RegionOfInterest.Value = 1234.56 '*okay, updates cell A1*
Set RegionOfInterest = Worksheets("Sheet1").Range("B5:D15")
RegionOfInterest.Columns(2).Value = "~~~~~~" '*okay*
'doSomethingToRows (RegionOfInterest) 'why do I get "OBJECT IS REQUIRED" error?
doSomethingToRows (Worksheets("Sheet1").Range("B5:C15")) 'but this executes okay
End Sub
From the msdn documentation of the Call keyword statement,
Remarks
You are not required to use the Call keyword when calling a procedure.
However, if you use the Call keyword to call a procedure that requires
arguments, argumentlist must be enclosed in parentheses. If you omit
the Call keyword, you also must omit the parentheses around
argumentlist. If you use either Call syntax to call any intrinsic or
user-defined function, the function's return value is discarded.
To pass a whole array to a procedure, use the array name followed by
empty parentheses.
From a practical standpoint, even though Subs can be called with or without the "Call" keyword, it makes sense to pick one way and stick with it as part of your coding style. I agree with Comintern - it is my opinion, based on observation of modern VBA code, that using the "Call" keyword should be considered deprecated. Instead, invoke Subs without parenthesis around the argument list.
And now the answer to the important question:
Why does your code throw an error?
Take for example the following Subroutine:
Public Sub ShowSum(arg1 As Long, arg2 As Long)
MsgBox arg1 + arg2
End Sub
We have established that, if not using the Call keyword, Subs must be invoked like so:
ShowSum 45, 37
What happens if it were instead called like ShowSum(45, 37)? Well, you wouldn't even be able to compile as VBA immediately complains "Expected =". This is because the VBA parser sees the parenthesis and decides that this must be a Function call, and it therefore expects you to be handling the return value with an "=" assignment statement.
What about a Sub with only one argument? For example:
Public Sub ShowNum(arg1 As Long)
MsgBox arg1
End Sub
The correct way to call this Sub is ShowNum 45. But what if you typed this into the VBA IDE: ShowNum(45)? As soon as you move the cursor off of the line, you'll notice that VBA adds a space between the Sub name and the opening parenthesis, giving you a crucial clue as to how the line of code is actually being interpreted:
ShowNum (45)
VBA is not treating those parenthesis as if they surrounded the argument list - it is instead treating them as grouping parenthesis. MOST of the time, this wouldn't matter, but it does in the case of Objects which have a default member.
To see the problem this causes, try running the following:
Dim v As Variant
Set v = Range("A1")
Set v = (Range("A1")) '<--- type mismatch here
Notice that you get a "Type Mismatch" on the marked line. Now add those two statements to the watch window and look at the "Type" column:
+-------------+-----+--------------+
| Expression |Value| Type |
+-------------+-----+--------------+
|Range("A1") | |Object/Range |
|(Range("A1"))| |Variant/String|
+-------------+-----+--------------+
When you surround an Object with grouping parenthesis, its default property is evaluated - in the case of the Range object, it is the Value property.
So it's really just a coincidence that VBA allowed you to get away with "putting parenthesis around the argumentlist" - really, VBA just interprets this as grouping parenthesis and evaluates the value accordingly. You can see by trying the same thing on a Sub with multiple parameters that it is invalid in VBA to invoke a Sub with parenthesis around the argument list.
#PaulG
Try this:
Public Sub Main()
Debug.Print TypeName(Range("A1"))
Debug.Print TypeName((Range("A1")))
End Sub
okay, I knew after I posted this question I'd be struck by lighting and receive an answer.
When passing an object VARIABLE to a sub-function and wishing to use parentheses "()", one must use CALL! Thus the correction to my code sample is:
**CALL doSomethingToRows(RegionOfInterest)**
Thank you!
Maybe we're talking about different things, but here's an example to make it a bit clearer what I mean.
Option Explicit
Sub TestDisplay()
Dim r As Range
'Create some range object
Set r = Range("A1")
'Invoke with Call.
Call DisplaySomething(r)
'Invoke without Call.
DisplaySomething r
End Sub
Sub DisplaySomething(ByVal Data As Range)
Debug.Print "Hi my type is " & TypeName(Data)
End Sub
Both calls work perfectly. One with Call and the other without.
Edit:
#Conintern. Thanks for explaining that. I see what is meant now.
However, I still respectively disagree.
If I declare the following:
Function DisplaySomething(ByVal Data As String)
DisplaySomething = "Hi my type is " & TypeName(Data)
End Function
and invoke it:
Debug.print DisplaySomething(Range("A1"))
I believe that Excel has been clever and converted to a string. It can do that by invoking the Default Parameter and can convert to a string.
However, as in the original parameter example, If I declare the following:
Function DisplaySomething(ByVal Data As Range)
DisplaySomething = "Hi my type is " & TypeName(Data)
End Function
There is no call on the Default Parameter, however it is called, because Excel was able to resolve it to that type.
Function DisplaySomething(ByVal Data As Double)
DisplaySomething = "Hi my type is " & TypeName(Data)
End Function
will return a double because it was able to coerce to a double.
Indeed in those examples the Default was called.
But in this example we are defining as Range. No Default called there however it is invoked - brackets or no brackets.
I believe this is more to do with Excel and data coercion.
Similar to the following:
Public Function Test(ByVal i As String) As Integer
Test = i
End Function
and invoking with:
Debug.print Test("1")
BTW, yes I know this isn't an object without a Default parmeter. Im pointing out data coercion. Excel does its best to resolve it.
Could be wrong mind you...
I'm trying to set up a sub to be called upon and use the value of its result in the main sub. So far I've been using Function to carry over the value. However, I was wondering if there are any alternative ways of doing the same thing? I figured ByVal/ByRef is another way to do it by using a Sub instead of Function. My current codes are as follow:
Sub Main()
Dim i as Long
i = lr("A")
'some other calculations using i
End Sub
Function lr(Tar As String) As Long
Dim twb As Workbook
Set twb = ThisWorkbook
lr = ThisWorkbook.Sheets(1).Range(Tar & Rows.Count).End(xlUp).Row
End Function
My question is, How would I write this if I were to use a Sub instead of Function? Thanks!
So far I've been using Function to carry over the value.
Great, that's what functions are for! When you only need to return a single value, the best way is always going to be a function.
Things get fuzzier when you start needing to return two or more values. You could:
Use ByRef parameters and use them as "out" values.
This is "ok" for procedures (Sub), and confusing for functions - what determines which parameter gets to be the function's return value, and which parameters get to be passed ByRef? How does the calling code know whether or not to pass an initialized value to those ByRef parameters?
A naming convention can help here:
Public Sub Foo(ByVal foo1 As String, ByRef outBar1 As String, ByRef outBar2 As String)
An "out" prefix can tell the calling code that the parameter is an out value.
Scope the variables at a level that is accessible by both the caller and the callee.
This is a bad practice that can easily lead to spaghetti code. Avoid it - variables should have the smallest necessary scope possible, and be passed between methods/functions/procedures/modules, not just globally scoped and accessed by anyone at any given time!
Create a class to encapsulate all the values the function should return.
Definitely more object-oriented, results in much cleaner, readable code. The only downside is that VBA doesn't really encourage you to do this, and consistently doing that will result in a myriad of classes that you can't quite organize.
I was shocked just a moment ago to discover that the following is legal (the C# equivalent is definitely not):
Class Assigner
''// Ignore this for now.
Public Field As Integer
''// This part is not so weird... take another instance ByRef,
''// assign it to a different instance -- stupid but whatever. '
Sub Assign(ByRef x As Assigner, ByVal y As Assigner)
x = y
End Sub
''// But... what's this?!?
Sub AssignNew()
''// Passing "Me" ByRef???
Assign(Me, New Assigner)
End Sub
''// This is just for testing.
Function GetField() As Integer
Return Me.Field
End Function
End Class
But what's even stranger just as strange to me is that it doesn't seem to do what I expect:
Dim a As New Assigner With {.Field = 10}
a.AssignNew()
Console.WriteLine(a.GetField())
The above outputs "10," not "0" like I thought it would (though naturally, this expectation was itself infused with a certain kind of horror). So it seems that you can pass Me ByRef, but the behavior is somehow overridden (?) by the compiler to be as if you had passed Me ByVal.
Why is it legal to pass Me ByRef? (Is there some backwards-compatibility explanation?)
Am I correct in saying that the behavior of doing this is overridden by the compiler? If not, what am I missing?
This behavior actually follows pretty directly from the Visual Basic specification.
11.4.3 Instance Expressions
An instance expression is the keyword Me, MyClass, or MyBase. An instance expression, which may only be used within the body of a non-shared method, constructor, or property accessor, is classified as a value.
9.2.5.2 Reference Parameters
If the type of the variable being passed to a reference parameter is not compatible with the reference parameter's type, or if a non-variable is passed as an argument to a reference parameter, a temporary variable may be allocated and passed to the reference parameter. The value being passed in will be copied into this temporary variable before the method is invoked and will be copied back to the original variable (if there is one) when the method returns.
(All emphasis mine)
So, the compiler will create a temporary variable assigned to the value of Me to be passed as the ByRef parameter. Upon return, no copy of the resulting value will take place since Me is not a variable.
It appears the compiler transforms "Me" into a variable which is then passed ByRef. If you compile your code, then open it with Reflector, you can see what's happening:
Class Assigner
''// Methods
Public Sub Assign(ByRef x As Assigner, ByVal y As Assigner)
x = y
End Sub
Public Sub AssignNew()
Dim VB$t_ref$S0 As Assigner = Me
Me.Assign((VB$t_ref$S0), New Assigner)
End Sub
Public Function GetField() As Integer
Return Me.Field
End Function
''// Fields
Public Field As Integer
End Class
So it looks like when you call AssignNew(), you are assigning the new instance to the internally generated variable. The "a" variable doesn't get touched because it's not even a part of the function.
This is just one of the thousands of possible 'almost errors' a programmer can make. MS caught most of them, in fact, sometimes I'm suprised at how many warnings do come up.
they missed this one.
As far as why it doesn't change 'me', it's a darn good thing! When you use 'me', it just passes a copy of the real class you are working with, for safety purposes. If this worked they way you were hoping, we would be talking GIANT side-effect. You're innocently working away with in your class' methods, and them BAM all of a sudden you are in an ENTIRELY different object! That would be awful! If you're going to do that, you might as well just write a piece of spagetti MS-Basic line-numbered code with all globals that get randomly set, and no subs/functions.
The way this works is the same way if you pass arguments in parenthesis. For example this works as expected:
Assign(Reference_I_Want_To_Set, New Assigner)
But this doesn't change anything:
Assign((Reference_I_Want_To_Set), New Assigner)
If you reflect the above type of code as adam101 suggests you will see similar results. While that is huge frustration with the parenthesis, it is a very good thing with Me !!!
what you need to do to make this code work is this:
Class Assigner
''// Ignore this for now.
Private newPropertyValue As Integer
Public Property NewProperty() As Integer
Get
Return newPropertyValue
End Get
Set(ByVal value As Integer)
newPropertyValue = value
End Set
End Property
''// This part is not so weird... take another instance ByRef,
''// assign it to a different instance -- stupid but whatever. '
Shared Sub Assign(ByRef x As Assigner, ByVal y As Assigner)
x = y
End Sub
''// But... what's this?!?
Shared Sub AssignNew(ByRef x As Assigner)
''// Passing "Me" ByRef???
Assign(x, New Assigner)
End Sub
End Class
then use it like
Dim a As New Assigner With {.NewProperty = 10}
Assigner.AssignNew(a)
my understanding is you cannot change the reference of the object while using it, so you need to change it in a shared sub
since Me cannot be the target of an assignment, the code seem to create a copy of it and from that point on, your not using the real object, but a copy of it