My question is this: why would I use a Property Get, Property Let, and Property Set in a vba class instead of a subroutine call. For instance if I have a class PersonCls with a variables:
Private name as String
Private age as Integer
What is the advantage of using the property syntax over something like this:
Public Sub Setname(nm as String)
name = nm
End Sub
Public Function Getname() as String
Getname = name
End Function
I've looked around and have not seen this explained very well (see VBA: Why Use Properties Instead of Subroutines or Functions?). Thanks in advance.
Because it's much simpler and more readable to write
myPerson.Name = myPerson.Name & " Jr."
As opposed to
myPerson.SetName(myPerson.GetName() & " Jr.")
Related
In a VBA class module (let's say in Excel or Access), I wrote a function SomeFunction() returning a value.
If I call this from another function/sub in the class, should I call it:
a) this way: myVar = SomeFunction or
b) this way: myVar = Me.SomeFunction ?
I think both work, so except for the writing style and clarifying SomeFunction is part of the class, does it make any difference?
Both are indeed valid, but way B should be preferred since it's more explicit what you're doing.
Consider the following (valid) class code:
Public Property Get SomeValue() As Integer
SomeValue = 5
End Property
Public Property Get AnotherValue() As Integer
Dim SomeValue As Integer
SomeValue = 3
AnotherValue = SomeValue 'Returns 3
Debug.Print Me.SomeValue 'Returns 5
End Property
Because you can (but shouldn't) do this in VBA, it's a good practice to use Me. to make it clear you're using a class property and not a variable.
As far as I know - It does not make any difference.
However, if you use Me. in the class, you can use the Intellisense to see the available subs, functions and properties, which could be a bit handy:
However, I prefer not to use the Me.
If you are having the following in a module:
Public Function Foo()
Foo = 5
End Function
Sub TestMe()
Dim cls As New Klasse1
cls.TestMe
End Sub
And then the following in Klasse1:
Sub TestMe()
Debug.Print Modul1.Foo
Debug.Print Me.Foo
Debug.Print Foo
End Sub
Function Foo()
Foo = 10
End Function
it is visible that the existense of Me. is just syntax sugar.
I've heard advice to change from User Defined Type (UDT) to a regular Class in order to overcome the limitations of UDT, such as not being able to use For Each with a UDT.
I've also heard advice to change from a regular Class to UDT to overcome the Class limitation where you can't pass things BYREF, like...
'Function:
Public Function RemoveArticle (ByRef strMovieTitle As String)
'Expected input is like "Terminator, The"
strMovieTitle = Left(... 'removes the article.
End Function
That works fine for this call:
Dim strMovieTitle As String
strMovieTitle = "Terminator, The"
RemoveArticle strMovieTitle
But not this call:
Dim objMovie As MovieClass
objMovie.strMovieTitle = "Terminator, The"
objMovie.strMovieGenre = "Sci-Fi"
InvertArticle objMovie.strMovieTitle
Even though MovieClass defines
strMovieTitle As String
I can't go changing RemoveArticle (and every simple little function like it) to take a MovieClass parameter instead of a String parameter because there are other UDTs or Classes and String Variables that also need to use RemoveArticle.
What do I do if I need to use For Each and I also need to pass ByRef?
Is there a way a Class can work around the parameter problem?
(Using Excel 2010.)
Now I have understood your concern.
You simply can't take that approach to meet your goal. As Tim Williams has commented in your question, your best bet would be something like this:
Dim objMovie As MovieClass
Dim strMovieTitle As String
strMovieTitle = "Terminator, The"
objMovie.strMovieTitle = InvertArticle(strMovieTitle)
However, I see that this still does not satisfy your need.
My suggestion is as follows:
make your object internal, target properties Private and expose them with Property Let and Property Get. This way you can do the modifications you want to the properties either on set or on get (from within the class... rather than fixing things from outside the class).
Aside note, in regards to create a helper class (as someone has recommended to you): you could join into one class all those functions you use widely, such as RemoveArticle or InvertArticle. However, it requires to create an instance object every time you want to use them and, therefore, does not combine well with the recommendation I am giving to you (if you want just to simplify code). So having them in a Module as you do now is fine. Just to clarify: those recommendations they gave to you are unrelated to your question here.
Example A: on set
In you class MovieClass, rename first all the instances of strMovieTitle to pStrMovieTitle and add this to your code:
Private pStrMovieTitle As String
Public Property Let strMovieTitle (strIn As String)
pStrMovieTitle = InvertArticle(strIn)
End Property
Public Property Get strMovieTitle As String
strMovieTitle = pStrMovieTitle
End Property
The usage would be something like this:
Dim objMovie As MovieClass
objMovie.strMovieTitle = "Terminator, The" ' the article position gets rectified on assignation
objMovie.strMovieGenre = "Sci-Fi"
'InvertArticle objMovie.strMovieTitle ' => you don't need to do this call
Example B: on get
To keep your original string as it comes, and do apply your helpers when you get the property value. That way you always preserve the original string. However, this approach will need more rework and it's only worthy in cases where you have lots of ways to use that String in different parts of your code.
Private pStrMovieTitleSource As String
Public Property Let strMovieTitle (strIn As String)
pStrMovieTitleSource = Trim(strIn)
End Property
Public Property Get strMovieTitleSource () As String
strMovieTitleSource = pStrMovieTitleSource
End Property
Public Property Get strMovieTitleRoot () As String
strMovieTitleRoot = RemoveArticle(pStrMovieTitleSource)
End Property
Public Property Get strMovieTitle () As String
strMovieTitle = InvertArticle(pStrMovieTitleSource)
End Property
Hope it helps
Hi I'm rather new to VBA I need to create an object with relativelly complicated Getter and Setter. To do this I am constantly checking with MSDN but clearly I am not understanding something because VBE keep highlighting lines starting and closing: Property (it appaently needs Get or Let??), Get(it apparently needs identifier), Let(it apparently needs identifier as well).
But I am trying to follow more concise notation where Get and Let methods are within a Property Statement which is used by Microsoft in its examples(see link above).
Can someone tell me where is my syntax wrong(or Microsoft's Documentation for that matter)???
Thank you
Private Matrix() As Vector
Property Transition()
Public Get(Old_S As String, New_S As String, Period As Integer) As Double
' Some Code
Return Matrix(Column, Row).Value(Period)
End Get
Public Let(Old_S As String, New_S As String, Vector_String As String)
' Some Code
Matrix(Row, Column).Value = Vector_String
End Let
End Property
You are reading the documentation for VB.NET. That's why you are confused. The syntax for properties in VBA is different. In VBA, the Get and Let for a property are not grouped together. They need to be listed separately, essentially like two separate methods:
Private mMyProperty As String
Public Property Get MyProperty() As String
MyProperty = mMyProperty
End Property
Public Property Let Transition(Value As String)
mMyProperty = Value
End Property
For VBA reference material, try starting here.
Your issue is that you are reading .Net help files! :)
Assuming you have a valid Vector class, your properties need to bde defined like this:
Private Matrix() As Vector
Public Property Get Transition(Old_S As String, New_S As String, Period As Integer) As String
' Some Code
Transition = Matrix(Column, Row).Value(Period)
End Property
Public Property Let Transition(Old_S As String, New_S As String, Period As Integer, Vector_String As String)
' Some Code
Matrix(Row, Column).Value = Vector_String
End Property
Note that the argument list for both procedures must match except that the Letter has an additional argument of the same type that the Getter returns.
It is also slightly unusual to have a Getter property that accepts arguments in VBA - that would more usually be implemented as a method.
Looks like you're using VB.Net syntax in VBA. That's not going to work, as they're entirely different languages. Here is a link to the proper documentation for the VBA Property Keyword.
Here is how you would write it in VBA.
Private Matrix() As Vector
Public Property Get MatrixValue(Old_S As String, New_S As String, Period As Integer) As Double
' Some Code
MatrixValue = Matrix(Column, Row).Value(Period)
End Property
Public Property Let MatrixValue(Old_S As String, New_S As String, Vector_String As String)
' Some Code
Matrix(Row, Column).Value = Vector_String
End Property
But you're going to have trouble with the Get property. You can pass parameters into Get, but it's not exactly intuitive. I think what you're really looking for is a function.
Public Function GetMatrixValue(Old_S As String, New_S As String, Period As Integer) As Double
' Some Code
MatrixValue = Matrix(Column, Row).Value(Period)
End Function
I have a requirement where I need to have a "type safe" way of accessing property names, without actually instantiating an object to get to the property. To give an example, consider a method that takes as arguments a list of IMyObject and a string that represents a property name (a property that exists in IMyObject).
The methods implementation will take the list and access all the objects in the list using the property name passed... for some reason or another, we won't dwell on that!!
Now, I know that you can do this using an instantiated object, something like ...
Dim x as MyObject = nothing
Dim prop As PropertyInfo = PropHelper.GetProperty(Of MyObject)(Function() x.MyProperty)
Where my helper method uses reflection to get the name of the property as a string - there are numerous examples of this flying around on the web!
But I don't want to have to create this pointless object, I just want to do something like MyObject.MyProperty! Reflection allows you to iterate through a types properties and methods without declaring an object of that type... but I want to access a specific property and retrieve the string version of its name without iteration and without declaring an object of that type!
The main point here is that although I am trying to get the property name as a string... this is done at run time... at compile time, I want this to be type safe so if someone changes the property name, the compilation will break.
Can anyone help in this quest!?!
So here is a quick code-listing to demonstrate the answer that I was looking for:
Imports System.Linq.Expressions
Public Class A
Public Prop1 As String
Public Prop2 As Integer
End Class
Public Class Form1
Public Function GetPropertyNameB(Of TModel, TProperty)(ByVal [property] As Expression(Of Func(Of TModel, TProperty))) As String
Dim memberExpression As MemberExpression = DirectCast([property].Body, MemberExpression)
Return memberExpression.Member.Name
End Function
Public Sub New()
InitializeComponent()
Dim propertyName As String = GetPropertyNameB(Function(myObj As A) myObj.Prop1)
Dim propertyName2 As String = GetPropertyNameB(Function(myObj As A) myObj.Prop2)
MsgBox(propertyName & " | " & propertyName2)
End
End Sub
End Class
You may be able to pass the property in as a simple lamdba expression, and take it in the method as an expression tree. You should be able to analyze the expression tree to get the string name of the property, but it the lambda expression will fail to compile if the property name changes. Check out this page for more details:
http://msdn.microsoft.com/en-us/library/bb397951.aspx
You can make use of the NameOf function:
Dim fieldName = nameOf(MyClass.MyField)
Is there anything wrong with the following code ? It failed on Form_Load() line , and complains about it.
Private Sub Form_Load()
Type Human
Name As String
End Type
Dim stu As Student
With Human:
.Name = "Someone"
End With
Debug.Print ("Name: " & stu.Name)
End Sub
You have two options:
1
Create a new class
Private Class Human
Public Name As String
End Class
(Obviously it would be better to wrap the Name in a public property, but for simplicity, exposing it as a public variable is easier.)
2
Create a new struct:
Structure Human
Dim Name As String
End Structure
Note
It should be noted that both of these options must be done outside of the function, not within Form_Load function
The keyword is no longer Type; it is Structure now. Type was used in VB6 and earlier, but not in .NET.