Basically I follow a spec to create functions in Access 2010. These functions are in VBA. When working with record sets the given declaration in the spec is
Dim obj.Recordset As New ADODB.Recordset
Yet every time I try and write it I get a syntax error so I just use:
Dim Recordset As object
I am not sure if this means the same thing but it compiles and seems to work fine. Basically my question is, is the given declaration for a recordset correct and is my alternative acceptable. Also Access 2010 is used as a user front end and the database is stored in MS- SQL server 2008 backend.
It looks like you are trying to define a variable with a '.' in the variable name. That is not a valid character in a variable name. If I didn't know better, this syntax looks like you are trying to somehow assign a data type of ADODB.Recordset to a property named 'Recordset' of a class object named 'obj' (which would be extremely bizarre and I don't know of a valid syntax for in VBA or why anyone would want to). I would expect the following will compile:
Dim rst As New ADODB.Recordset
Also make sure you have added the appropriate reference in Tools --> References (Microsoft ActiveX Data Objects 2.0 Library or other latest version). As to your second question, that should be a viable alternative but I prefer the strongly typed former.
According to the Microsoft documentation, to determine the number of characters in str, use the Len function. If used in a Windows Form, or any other class that has a Right property, you must fully qualify the function with "Microsoft.VisualBasic.Strings.Right".
If I set "Imports Microsoft.VisualBasic" at the top of the form I still have to use the fully qualified name in my code. Why does MS require this?
Because, without the fully qualified name, if there are two methods with the same name, the compiler cannot choose one over the other. So you should take care of the problem giving the correct hint
To ease your typing you could add at the top of your code file this version of the Imports statement
Imports VB6 = Microsoft.VisualBasic
and then you could type
Dim stringLen = VB6.Len(yourStringVariable)
This is the MSDN introduction to Namespaces in VB.NET, in particular, in the first lines of the article is explained your problem Avoiding Namespaces Collisions
NET Framework namespaces address a problem sometimes called namespace
pollution, in which the developer of a class library is hampered by
the use of similar names in another library. These conflicts with
existing components are sometimes called name collisions.
For example, if you create a new class named ListBox, you can use it
inside your project without qualification. However, if you want to use
the .NET Framework ListBox class in the same project, you must use a
fully qualified reference to make the reference unique. If the
reference is not unique, Visual Basic produces an error stating that
the name is ambiguous.
And by the way, start to use the equivalent framework methods for Right, Left, and Len.
They are still available only to help the porting of old VB6 application, (and sometime they work differently). In new applications I suggest to use
string.Substring(start, len)
string.Length
A winform, Form (derived from Control), have properties named Right and Left.
Public Class Form1
Inherits Form
Public Sub Test()
Dim location_left As Integer = Me.Left
Dim location_right As Integer = Me.Right
'Or simply:
location_left = Left '<- (Referring to Me.Left, not Microsoft.VisualBasic.Strings.Left)
location_right = Right '<- (Referring to Me.Right, not Microsoft.VisualBasic.Strings.Right)
End Sub
End Class
Therefore you'll need the use the full qualify name.
This seems like a simple question but I after chasing forums for several hours I think it might be impossible.
I often want to convert a program from early binding to late binding. Usually, it is a vba, visual basic for applications, program that runs under Excel 2010 and windows 7 pro.
For discussion purposes, let’s pretend it is the following.
Sub EarlyBind()
' use IDE > Tools > references > and select “Microsoft Internet Controls”
Dim shellWins1 as shdocvw.shellwindows
Line1: Set shellWins1 = New SHDocVw.ShellWindows
MsgBox TypeName(shellWins1) ' this will display “IShellWindows”
' other code that expects to be working with an IshellWindows object …..
End Sub
In my experience, converting such a program to late binding is sometimes hard.
For instance, I found some forums that suggest I change it to
Set shellwins1 = createobject("Shell.applicaton")
But that creates a IShellDispatch5 object, not an IshellWindows object. That means I have to change other code to accommodate the new object type. And, of course I have to test that other code for subtle differences.
So, my goal is to find a general solution that will allow me to rewrite “Line1” to create the CORRECT object type with late binding. I also wish to avoid the need setting a reference to "Microsof Internet Controls. In other words, I want the code to look like this:
Sub LateBind()
Dim shellWins1 as object
Line1: Set shellWins1 = createobject(“xxxxxx.yyyyyy”).zzzzzz
MsgBox TypeName(shellWins1) ‘ this should display “IShellWindows”
….. other code that expects to be working with an IshellWindows object …..
End Sub
I know how to use the vba IDE to find the dll associated with the object. In this case the dll is Library SHDocVw C:\Windows\SysWOW64\ieframe.dll.
I have installed OleView and can find the associated IshellWindows “magic numbers” for the clsId, TypeLib, and Inteface (for instance the interface is 85CB6900-4D95-11CF-960C-0080C7F4EE85).
But, I don’t know how to convert them into a program id that can be used in line1 in the sample code posted above.
I hope someone here can help.
------ With MeHow's help, I now have the answer! ------
To switch 'set myObj = new xxxx.yyyyy' to late binding for arbitrary object types
Change set myObj = new xxxx.yyyyy
into set myObj = CreateObject("xxxx.yyyyy")
Very often that will work.
But, in the some cases, (e.g. "shDocVw.ShellWindows.") it gives error 429 ActiveX component cannot be created.
When that occurs I AM COMPLETELY OUT OF LUCK. It is impossible to use late binding with that EXACT object class. Instead I must find a substitute class that does approximately the same thing. (e.g. "Shell.Application").
Your short answer is
IShellWindows is an interface.
It
Provides access to the collection of open Shell windows.
Therefore
Take a look at the CreateObject() method.
Note:
Creates and returns a reference to a COM object. CreateObject cannot
be used to create instances of classes in Visual Basic unless those
classes are explicitly exposed as COM components.
IShellWindows is not exposed as a COM component so that's why there is no way to say CreateObject("SHDocVw.IShellWindows")
When you open your registry (regedit) and search for a key type in IShellWindows. If you find anything that means you've found your Prog ID and if you don't find anything it means that nothing like IShellWindows is registered as a prog Id therefore it would make sense to assume that you can't late bind IShellWindows
I bumped into your question trying to find something for myself. But I don't know if you have tried the following -
Set shellwins1 = createobject("Shell.Application")
MsgBox TypeName(shellWins1.Windows)
This answers your question for datatype. It prints IShellWindows for me. I'm not sure though if it could actually solve your purpose for latebinding meaning if this would be the object required though the datatype is what you need.
So, I would advise you to give it a try.
There is a slightly better approach outlined at https://www.experts-exchange.com/questions/28961564/How-to-find-the-class-id-of-an-arbitrary-object-Example-Set-x-CreateObject-New-1C3B4210-F441-11CE-B9EA-00AA006B1A69.html#a41743468.
This question already has answers here:
Why can I access an item in KeyCollection/ValueCollection by index even if it doesn't implement IList(Of Key)?
(2 answers)
Closed 6 years ago.
I have a VB.NET project where I am able to iterate through the keys and values collections of a dictionary object using an index:
MyDictionary.Keys(idx)
MyDictionary.Values(idx)
When this code is taken from the test project and placed into the real project I get the following error:
'System.Collections.Generic.Dictionary(Of Double, String).KeyCollection' cannot be indexed because it has no default property.
and
'System.Collections.Generic.Dictionary(Of Double, String).ValueCollection' cannot be indexed because it has no default property.
This is using VB.NET and VS 2008. I don't know what the difference would be from one project to the next that would cause this error. The test is a console application and the program is a winforms app.
What conditions would cause the default property of these collections to change?
Edit - Thank you for all of the answers that tell me how to loop through a dictionary. Those, answers, however, do not answer my question of why I can use an index in one project and not the other. Should I not be able to copy and paste the code from one .net project to another and have it work the same? And, no, option strict, is not the cause of the problem.
Edit - Attempt to reproduce what I'm seeing:
Create a new VB.NET Console Application using VS 2008
Copy and paste the following code into the module:
Imports System.Collections
Imports System.Collections.Generic
Module Module1
Public dtf As Dictionary(Of Double, String)
Public Sub BuildDictionary()
dtf = New Dictionary(Of Double, String)
dtf.Add(1.0, "1")
dtf.Add(0.0, "0")
End Sub
Public Sub Search()
For idx As Integer = 0 To dtf.Keys.Count - 1
If dtf.Keys(idx) = 0 Then
Exit Sub
End If
Next
End Sub
Sub Main()
End Sub
End Module
In the line in sub search that says "dtf.Keys(idx) = 0" place your cursor after the right parenthesis and backspace you should get a tooltip that says, "<Extension> ElementAtOrDefault(index as Integer) as Double - index: the zero based element of the index to retrieve.
I am not getting that in my other project. Even though it seem I have the same references and settings.
KeyCollection does not implement indexers like that, you must enumerate through the MyDictionary.Keys.
c#
foreach(double key in MyDictionary.Keys)
Console.Write( MyDictionary[ key ] )
vb
For Each key As Double in MyDictionary.Keys
Console.Write( MyDictionary( key )
Next key
Looping with a for(;i++;) wouldn't be the correct way of going through your hashtable (dictionary) since it is not an array it really has no concept of an array index (array[index])
I bet your real project had OPTION STRICT ON, as all projects should, and that your test project had it OFF. That's why you didn't get a compiler error in your test project.
EDIT: the poster says he has OPTION STRICT ON for both projects. That makes this more interesting.
I still think the most likely reason for this difference is that in one case, the compiler compiled the code and saw the error; but in the other case, the compiler didn't comile the code. Is this the same version of Visual Studio on the same machine at the same time? Same .NET Framework version in both cases?
Are these both the same type of project, for instance, are they both console applications? I ask because ASP.NET Web Site "projects" usually don't attempt to compile code until the code is called. If your test project were such a "project", and if you didn't actualy test the code (that is, if you didn't actually step into this code and see it work), then you might have assumed that the fact you could press F5 meant that all the code was compiled, when it wasn't.
My next thoughts would be to see if MyDictionary was really of the same type in both cases.
Beyond that, if you really need to know why this happened, I'd make a copy of the "real" project, and start changing it to be more and more like the test project. This would probably be a matter of mass deletions at first. I'd keep changing it either until the problem was found, or until the two were identical.
EDIT 2: The default console project imports the System.Linq namespace (see the "References" tab in project properties). This import brings the ElementAtOrDefault extension method into scope. This extension method extends IEnumerable(Of T); in your case IEnumerable(Of Double), which is what the Keys property implements.
What surprises me about this is that VB.NET is automatically applying this extension method. In C#, the method would need to be explicitly named.
If you remove the Import of System.Linq, you'll find that your test application gets the same error as the production application.
The Keys and Values property of Dictionary(Of TKey,TValue) do not have an indexer property. They are implementations of ICollection vs. IList and hence don't support accesses by Index. If you want to iterate through a Dictionary, the best way is a For Each loop.
For Each pair in MyDictionary
Dim key = pair.Key
Dim value = pair.Value
Next
EDIT
Have you checked to make sure that System.Core is referenced in both projects and that you have a project level imports for System.Linq? That's the only thing I can think of that would produce a difference in ElementAtOrDefault which is a method inside of system.Core.
I'm still a bit baffled why that method would be bound to for a simple indexer. Going to look into that
When is it appropriate to use a class in Visual Basic for Applications (VBA)?
I'm assuming the accelerated development and reduction of introducing bugs is a common benefit for most languages that support OOP. But with VBA, is there a specific criterion?
It depends on who's going to develop and maintain the code. Typical "Power User" macro writers hacking small ad-hoc apps may well be confused by using classes. But for serious development, the reasons to use classes are the same as in other languages. You have the same restrictions as VB6 - no inheritance - but you can have polymorphism by using interfaces.
A good use of classes is to represent entities, and collections of entities. For example, I often see VBA code that copies an Excel range into a two-dimensional array, then manipulates the two dimensional array with code like:
Total = 0
For i = 0 To NumRows-1
Total = Total + (OrderArray(i,1) * OrderArray(i,3))
Next i
It's more readable to copy the range into a collection of objects with appropriately-named properties, something like:
Total = 0
For Each objOrder in colOrders
Total = Total + objOrder.Quantity * objOrder.Price
Next i
Another example is to use classes to implement the RAII design pattern (google for it). For example, one thing I may need to do is to unprotect a worksheet, do some manipulations, then protect it again. Using a class ensures that the worksheet will always be protected again even if an error occurs in your code:
--- WorksheetProtector class module ---
Private m_objWorksheet As Worksheet
Private m_sPassword As String
Public Sub Unprotect(Worksheet As Worksheet, Password As String)
' Nothing to do if we didn't define a password for the worksheet
If Len(Password) = 0 Then Exit Sub
' If the worksheet is already unprotected, nothing to do
If Not Worksheet.ProtectContents Then Exit Sub
' Unprotect the worksheet
Worksheet.Unprotect Password
' Remember the worksheet and password so we can protect again
Set m_objWorksheet = Worksheet
m_sPassword = Password
End Sub
Public Sub Protect()
' Protects the worksheet with the same password used to unprotect it
If m_objWorksheet Is Nothing Then Exit Sub
If Len(m_sPassword) = 0 Then Exit Sub
' If the worksheet is already protected, nothing to do
If m_objWorksheet.ProtectContents Then Exit Sub
m_objWorksheet.Protect m_sPassword
Set m_objWorksheet = Nothing
m_sPassword = ""
End Sub
Private Sub Class_Terminate()
' Reprotect the worksheet when this object goes out of scope
On Error Resume Next
Protect
End Sub
You can then use this to simplify your code:
Public Sub DoSomething()
Dim objWorksheetProtector as WorksheetProtector
Set objWorksheetProtector = New WorksheetProtector
objWorksheetProtector.Unprotect myWorksheet, myPassword
... manipulate myWorksheet - may raise an error
End Sub
When this Sub exits, objWorksheetProtector goes out of scope, and the worksheet is protected again.
I think the criteria is the same as other languages
If you need to tie together several pieces of data and some methods and also specifically handle what happens when the object is created/terminated, classes are ideal
say if you have a few procedures which fire when you open a form and one of them is taking a long time, you might decide you want to time each stage......
You could create a stopwatch class with methods for the obvious functions for starting and stopping, you could then add a function to retrieve the time so far and report it in a text file, using an argument representing the name of the process being timed. You could write logic to log only the slowest performances for investigation.
You could then add a progress bar object with methods to open and close it and to display the names of the current action, along with times in ms and probable time remaining based on previous stored reports etc
Another example might be if you dont like Access's user group rubbish, you can create your own User class with methods for loging in and out and features for group-level user access control/auditing/logging certain actions/tracking errors etc
Of course you could do this using a set of unrelated methods and lots of variable passing, but to have it all encapsulated in a class just seems better to me.
You do sooner or later come near to the limits of VBA, but its quite a powerful language and if your company ties you to it you can actually get some good, complex solutions out of it.
Classes are extremely useful when dealing with the more complex API functions, and particularly when they require a data structure.
For example, the GetOpenFileName() and GetSaveFileName() functions take an OPENFILENAME stucture with many members. you might not need to take advantage of all of them but they are there and should be initialized.
I like to wrap the structure (UDT) and the API function declarations into a CfileDialog class. The Class_Initialize event sets up the default values of the structure's members, so that when I use the class, I only need to set the members I want to change (through Property procedures). Flag constants are implemented as an Enum. So, for example, to choose a spreadsheet to open, my code might look like this:
Dim strFileName As String
Dim dlgXLS As New CFileDialog
With dlgXLS
.Title = "Choose a Spreadsheet"
.Filter = "Excel (*.xls)|*.xls|All Files (*.*)|*.*"
.Flags = ofnFileMustExist OR ofnExplorer
If OpenFileDialog() Then
strFileName = .FileName
End If
End With
Set dlgXLS = Nothing
The class sets the default directory to My Documents, though if I wanted to I could change it with the InitDir property.
This is just one example of how a class can be hugely beneficial in a VBA application.
I use classes if I want to create an self-encapsulated package of code that I will use across many VBA projects that come across for various clients.
I wouldn't say there's a specific criterion, but I've never really found a useful place to use Classes in VBA code. In my mind it's so tied to the existing models around the Office apps that adding additional abstraction outside of that object model just confuses things.
That's not to say one couldn't find a useful place for a class in VBA, or do perfectly useful things using a class, just that I've never found them useful in that environment.
For data recursion (a.k.a. BOM handling), a custom class is critically helpful and I think sometimes indispensable. You can make a recursive function without a class module, but a lot of data issues can't be addressed effectively.
(I don't know why people aren't out peddling BOM library-sets for VBA. Maybe the XML tools have made a difference.)
Multiple form instances is the common application of a class (many automation problems are otherwise unsolvable), I assume the question is about custom classes.
I use classes when I need to do something and a class will do it best:) For instance if you need to respond to (or intercept) events, then you need a class. Some people hate UDTs (user defined types) but I like them, so I use them if I want plain-english self-documenting code. Pharmacy.NCPDP being a lot easier to read then strPhrmNum :) But a UDT is limited, so say I want to be able to set Pharmacy.NCPDP and have all the other properties populate. And I also want make it so you can't accidentally alter the data. Then I need a class, because you don't have readonly properties in a UDT, etc.
Another consideration is just simple readability. If you are doing complex data structures, it's often beneficial to know you just need to call Company.Owner.Phone.AreaCode then trying to keep track of where everything is structured. Especially for people who have to maintain that codebase 2 years after you left:)
My own two cents is "Code With Purpose". Don't use a class without a reason. But if you have a reason then do it:)
You can also reuse VBA code without using actual classes. For example, if you have a called, VBACode. You can access any function or sub in any module with the following syntax:
VBCode.mysub(param1, param2)
If you create a reference to a template/doc (as you would a dll), you can reference code from other projects in the same way.
Developing software, even with Microsoft Access, using Object Oriented Programming is generally a good practice. It will allow for scalability in the future by allowing objects to be loosely coupled, along with a number of advantages. This basically means that the objects in your system will be less dependent on each other, so refactoring becomes a lot easier. You can achieve this is Access using Class Modules. The downside is that you cannot perform Class Inheritance or Polymorphism in VBA. In the end, there's no hard and fast rule about using classes, just best practices. But keep in mind that as your application grows, the easier it is to maintain using classes.
As there is a lot code overhead in using classes in VBA I think a class has to provide more benefit than in other languages:
So this are things to consider before using a class instead of functions:
There is no class-inheritance in vba. So prepare to copy some code when you do similar small things in different classes. This happens especially when you want to work with interfaces and want to implement one interfaces in different classes.
There are no built in constructors in vba-classes. In my case I create a extra function like below to simulate this. But of curse, this is overhead too and can be ignored by the one how uses the class. Plus: As its not possible to use different functions with the same name but different parameters, you have to use different names for your "constructor"-functions. Also the functions lead to an extra debug-step which can be quite annoying.
Public Function MyClass(ByVal someInit As Boolean) As MyClassClass
Set MyClass = New MyClassClass
Call MyClass.Init(someInit)
End Function
The development environment does not provide a "goto definition" for class-names. This can be quite annoying, especially when using classes with interfaces, because you always have to use the module-explorer to jump to the class code.
object-variables are used different to other variable-types in different places. So you have to use a extra "Set" to assign a object
Set varName = new ClassName
if you want to use properties with objects this is done by a different setter. You have to use "set" instead of "let"
If you implement an interface in vba the function-name is named "InterfaceName_functionName" and defined as private. So you can use the interface function only when you cast the Variable to the Interface. If you want to use the function with the original class, you have to create an extra "public" function which only calls the interface function (see below). This creates an extra debug-step too.
'content of class-module: MyClass
implements IMyInterface
private sub IMyInterface_SomeFunction()
'This can only be called if you got an object of type "IMyInterface"
end function
private sub IMyInterface_SomeFunction()
'You need this to call the function when having an object of the type "MyClass"
Call IMyInterface_SomeFunction()
end function
This means:
I !dont! use classes when they would contain no member-variables.
I am aware of the overhead and dont use classes as the default to do things. Usually functions-only is the default way to do things in VBA.
Examples of classes I created which I found to be useful:
Collection-Classes: e.g. StringCollection, LongCollection which provide the collection functionality vba is missing
DbInserter-Class: Class to create insert-statements
Examples of classes I created which I dont found to be useful:
Converter-class: A class which would have provided the functionality for converting variables to other types (e.g. StringToLong, VariantToString)
StringTool-class: A class which would have provided some functionality for strings. e.g. StartsWith
You can define a sql wrapper class in access that is more convenient than the recordsets and querydefs. For example if you want to update a table based on a criteria in another related table, you cannot use joins. You could built a vba recorset and querydef to do that however i find it easier with a class. Also, your application can have some concept that need more that 2 tables, it might be better imo to use classes for that. E.g. You application track incidents. Incident have several attributes that will hold in several tables {users and their contacts or profiles, incident description; status tracking; Checklists to help the support officer to reply tonthe incident; Reply ...} . To keep track of all the queries and relationships involved, oop can be helpful. It is a relief to be able to do Incident.Update(xxx) instead of all the coding ...
In VBA, I prefer classes to modules when:
(frequent case) I want multiple simultaneous instances (objects) of a common structure (class) each with own independent properties.
Example:Dim EdgeTabGoogle as new Selenium.EdgeDriverDim EdgeTabBing as new
Selenium.EdgeDriver'Open both, then do something and read data to and from both, then close both
(sometimes) I want to take advantage of the Class_Initialize and Class_Terminate automatic functions
(sometimes) I want hierarchical tree of procedures (for just variables a chain of "Type" is sufficient), for better readability and Intellisense
(rarely) I want public variables or procedures to not show in Intellisense globally (unless preceded by the object name)
I don't see why the criteria for VBA would be any different from another language, particularly if you are referring to VB.NET.