In my previous question, How do I assign a value to a property where the property name is supplied at runtime in VBA?, I learned to use CallByName to set a property in a class at run time.
This time, however, I'm trying to figure out how to get an object at run time from a string.
For example, let's say I have a string with the following data: Worksheets("RAW DATA").Range("A1").QueryTable.
Here's what I might try to do where the data above is the input for strParam below:
Function GetObject(strParam As String) As Object
GetObject = SomeFunction(strParam)
End Function
In this case, GetObject should return a QueryTable when evaluated against Worksheets("RAW DATA").Range("A1").QueryTable. Is there anything in VBA that could take the place of SomeFunction from the example above?
Active Scripting Engine can help you. Instantiate ScriptControl ActiveX, use .AddObject() method to add reference to Excel's Application object to the script control's execution environment, set the third parameter to True to make all Application's members accessible too. Then just use .Eval() method to evaluate any property or method, which is the Application's member. The example below shows evaluation of Worksheets() property:
Sub TestQueryTable()
Dim objQueryTable As QueryTable
Dim strEvalContent As String
strEvalContent = "Worksheets(""RAW DATA"").Range(""A1"").QueryTable"
Set objQueryTable = EvalObject(strEvalContent)
objQueryTable.Refresh
MsgBox objQueryTable.Connection
End Sub
Function EvalObject(strEvalContent As String) As Object
With CreateObject("ScriptControl")
.Language = "VBScript"
.AddObject "app", Application, True
Set EvalObject = .Eval(strEvalContent)
End With
End Function
If you are on 64-bit Office, this answer may help you to get ScriptControl to work.
This time you're out of luck. There is no VBA equivalent of eval (not in Excel anyway...there is in Access VBA).
(Application.Evaluate() evaluates strings as Excel expressions, not as VBA code.)
There's the "Evaluate" method (or [ ] brackets). I don't think it will do exactly what you expect - as in run VBA code found in a string. You can look it up in the VBA help menu.
Related
Say you have one slide with one chart on it, and you run this code(in a version of Office later than 2007):
Dim pptWorkbook As Object
Dim result As Object
Set pptWorkbook = ActivePresentation.slides(1).Shapes(1).Chart.ChartData.Workbook
Set result = pptWorkbook.ContentTypeProperties
You will generate an error:
Application-defined or object-defined error
I believe this is because "Smart tags are deprecated in Office 2010."(Source), Generally to avoiding this sort of issue from throwing an error and exiting your VBA you can take one of two different approaches:
//Method 1
If OfficeVersion <= 2007
Set result = pptWorkbook.ContentTypeProperties
//Method 2
On Error Resume Next // or GOTO error handler
Set result = pptWorkbook.ContentTypeProperties
Method one requires that you know the specific reason why the property would cause an error, which is easy in this case but may not be as easy with other properties. Method two requires that you use some form of error handling to deal with the error AFTER the fact, my understanding of most other Microsoft languages is that is typically discouraged(example, another example). Is this standard practice in VBA?
In VBA, is there any other way to determine whether a property of an object would throw an error if invoked, BEFORE invoking that property, and without knowing the specifics of that invoked property?
What I like to do for this situation is create a separate function that checks if the property exists and returns a Boolean. In this case it would look something like this:
Public Function CheckIfExists(targetObj As Object) As Boolean
Dim testObj As Object
On Error GoTo failedTest:
Set testObj = targetObj.ContentTypeProperties
CheckIfExists = True
Exit Function
failedTest:
CheckIfExists = False
End Function
Which would return false if that property causes an error and true if not-
Then modify your sub to be:
Public Sub FooSub()
Dim pptWorkbook As Object
Dim result As Object
Set pptWorkbook = ActivePresentation.slides(1).Shapes(1).Chart.ChartData.Workbook
If CheckIfExists(pptWorkbook) Then
Set result = pptWorkbook.ContentTypeProperties
End If
... rest of your code or appropriate error handling...
Hope this helps,
TheSilkCode
I have dificulties figuring how a function can return an object in Excel VBA.
For example, in Java, I am used to write it like this:
Private ArrayList<> getARandomArrayList() {
//... My code
return anArrayList;
}
This method should return an arrayList that I can use.
If I do this in Excel, I believe it is supposed to look like this:
Function getARandomArrayList() As System.Collections.ArrayList
'... My code
getARandomArrayList = anArrayList
End Function
When I try to use this kind of function, I get a "Compile error: User-defined type not defined" error window. If I use variables type like Double or String, I have no problem. It is only with objects that I get errors.
A VBA.Collection may work for you, depending on your needs. (Edit: And as Vincent points out in the comments, no additional references are required.) Here's what it'd look like to use one:
Function getSomeCollection() As VBA.Collection
'Declare a collection
Dim newCollection As VBA.Collection
'Initialize the collection
Set newCollection = New VBA.Collection
'Add a string.
'Other methods are Item (access by index), Count, and Remove (by index)
newCollection.Add "hello"
'Reference the collection (note it's 1-based)
MsgBox newCollection(1)
'Set the return value
Set getSomeCollection = newCollection
End Function
As Rory said:
You have to set a reference to the relevant object library in order to be able to declare a variable as a type contained in it
I went in reference and activated System librairies.
I'm working in Excel 2010 VBA. Is there a way of accessing values in global variables declared outside a userform, in code inside the userform? Code inside my userform returns the global variable as null - can't work out why!
The variable is declared in the ThisWorkbook module as:
Public TargetCell As Range
Public TargetCellWorksheet as Worksheet
Public CurrentValue As Long
Inside the userform, I have this code on the "Update" button:
Private Sub Update_Click()
MsgBox ("Start of Update sub. TargetCellWorksheet =" & TargetCellWorksheet)
End Sub
The msgbox returns "" for the variable.
Hoping someone may be able to help me understand this and how to access the variable inside the userform? Thank you in advance
As for the problem itself, you declare
Public TargetCellWorksheet as Worksheet
and then try to show it into a MsgBox:
MsgBox ("Start of Update sub. TargetCellWorksheet =" & TargetCellWorksheet)
Did you maybe mean TargetCellWorksheet.Name, or TargetCellWorksheet.Range("A1").Value, since the MsgBox expects to receive a string?
However, if you're sure about your code, it might depend on the fact that the variable is not properly declared as Public and it goes at module level only. You might want to add a property to your form, if the variable is part of the form itself (I assume that you meant to use CurrentValue, but you can simply change the type of the property from Long to Worksheet and use it instead):
This goes inside the code of your form
Dim pCurrentValue As Long
Public Property Get CurrentValue() As Long
CurrentValue = pCurrentValue
End Property
Public Property Let CurrentValue (value As Long)
pCurrentValue = value
End Property
Hence, passing the variable from the module to the form like this:
This goes into your module, before you enter the code of the form
Dim myForm As New yourForm
myForm.CurrentValue = whateverYourVariableIs
and so using the variable inside your form like this:
You can hence use your variable by calling it from the property of the form
myVariableInTheForm = Me.CurrentValue
I must say that, however, it is strange that a public variable is not reaching the stack of the form. Are you sure you're not only declaring the variable without assigning any value before?
I have been looking through old code to get familiar with the system I use and found a piece of code that I feel can be used better.
What goes on here is some data gets added to the collection(around 150 string variables, some with two variables(variableName/VariableValue), most with only one(VariableName)). It will try to set a module level string variable to the item of the collection passing it the index(variableName) then if there's a value setting the VariableVAlue to the module level variable.
What I feel needs work is that if the collection is passed a variable and the variable doesn't have a value it will return a "" which would cause a runtime error hence there's a On Error GoTo Handler code to manually add a "" to the collection. I feel there's a better way to do this rather than knowing there will be a runtime issue then solving it after catching it. Would there be a way to have a return "" not throw an exception or would the use of an Array also work here since it's a "collection" as well?
Here's an example to try to help visualize:
Public Function GetCollectionVariable(ByVal varName as string) as String
If collection1 Is Nothing Then
m_collection1 = New Collection
End If
On Error GoTo Handler
GetCollectionVariable = collection1.Item(VarName)
exit function
Handler:
collection1.add("", VarName)
GetCollectionVariable = ""
End FUnction
Thanks for your time!!
If Collection1 is a dictionary, you can use TryGetValue.
I have a collection inside a class module. I'd like to restrict the object type that is "addable" to this collection, i.e. collection should only ever accept objects of one given type and nothing else.
Is there any way to enforce the type of objects added to a collection?
From what I can tell, there is no built-in way to do this. Is the solution then to make this collection private, and build wrapper functions for the methods usually accessible for Collections, i.e. Add, Remove, Item, and Count?
I kinda hate having to write 3 wrapper functions that add no functionality, just to be able to add some type enforcement to the Add method. But if that's the only way, then that's the only way.
There is no way to avoid wrapper functions. That's just inherent in the "specialization through containment/delegation" model that VBA uses.
You can build a "custom collection class", though. You can even make it iterable with For...Each, but that requires leaving the VBA IDE and editing source files directly.
First, see the "Creating Your Own Collection Classes" section of the old Visual Basic 6.0 Programmer's Guide:
http://msdn.microsoft.com/en-us/library/aa262340(v=VS.60).aspx
There is also an answer here on stackoverflow that describes the same thing:
vb6 equivalent to list<someclass>
However, those are written for VB6, not VBA. In VBA you can't do the "procedure attributes" part in the IDE. You have to export the class module as text and add it in with a text editor. Dick Kusleika's website Daily Dose of Excel (Dick is a regular stackoverflow contributer as you probably know) has a post from Rob van Gelder showing how to do this:
http://www.dailydoseofexcel.com/archives/2010/07/04/custom-collection-class/
In your case, going to all that trouble - each "custom collection" class needs its own module - might not be worth it. (If you only have one use for this and it is buried in another class, you might find that you don't want to expose all of the functionality of Collection anyway.)
This is what I did. I liked Rob van Gelder's example, as pointed to by #jtolle, but why should I be content with making a "custom collection class" that will only accept one specific object type (e.g. People), forever? As #jtolle points out, this is super annoying.
Instead, I generalized the idea and made a new class called UniformCollection that can contain any data type -- as long as all items are of the same type in any given instance of UniformCollection.
I added a private Variant that is a placeholder for the data type that a given instance of UniformCollection can contain.
Private mvarPrototype As Variant
After making an instance of UniformCollection and before using it, it must be initialized by specifying which data type it will contain.
Public Sub Initialize(Prototype As Variant)
If VarType(Prototype) = vbEmpty Or VarType(Prototype) = vbNull Then
Err.Raise Number:=ERR__CANT_INITIALIZE, _
Source:=TypeName(Me), _
Description:=ErrorDescription(ERR__CANT_INITIALIZE) & _
TypeName(Prototype)
End If
' Clear anything already in collection.
Set mUniformCollection = New Collection
If VarType(Prototype) = vbObject Or VarType(Prototype) = vbDataObject Then
' It's an object. Need Set.
Set mvarPrototype = Prototype
Else
' It's not an object.
mvarPrototype = Prototype
End If
' Collection will now accept only items of same type as Prototype.
End Sub
The Add method will then only accept new items that are of the same type as Prototype (be it an object or a primitive variable... haven't tested with UDTs yet).
Public Sub Add(NewItem As Variant)
If VarType(mvarPrototype) = vbEmpty Then
Err.Raise Number:=ERR__NOT_INITIALIZED, _
Source:=TypeName(Me), _
Description:=ErrorDescription(ERR__NOT_INITIALIZED)
ElseIf Not TypeName(NewItem) = TypeName(mvarPrototype) Then
Err.Raise Number:=ERR__INVALID_TYPE, _
Source:=TypeName(Me), _
Description:=ErrorDescription(ERR__INVALID_TYPE) & _
TypeName(mvarPrototype) & "."
Else
' Object is of correct type. Accept it.
' Do nothing.
End If
mUniformCollection.Add NewItem
End Sub
The rest is pretty much the same as in the example (plus some error handling). Too bad RvG didn't go the whole way! Even more too bad that Microsoft didn't include this kind of thing as a built-in feature...
I did almost the same code of Jean-François Corbett, but I adapted because for some reason wasn't working.
Option Explicit
Public pParametro As String
Private pColecao As New Collection
Public Sub Inicializar(ByVal parametro As String)
pParametro = parametro
End Sub
Public Sub Add(NewItem As Object)
If TypeName(NewItem) <> pParametro Then
MsgBox "Classe do objeto não é compatível à coleção"
Else
pColecao.Add NewItem
End If
End Sub
Public Property Get Count() As Long
Count = pColecao.Count
End Property
Public Property Get Item(NameOrNumber As Variant) As Variant
Set Item = pColecao(NameOrNumber)
End Property
Sub Remove(NameOrNumber As Variant)
pColecao.Remove NameOrNumber
End Sub
Then, when i want to create an instance from CCollection I make like the code bellow:
Set pFornecedores = New CCollection
pFornecedores.Inicializar ("CEmpresa")
Where CEmpresa is the class type from the object I want
Yes. The solution is to make your collection private and then make public wrapper functions to add, remove, getitem and count etc.
It may seem like hassle to write the additional code but it is a more robust solution to encapsulate the collection like this.