Visual Basic for Applications: Difference between revisions

Visual Basic for Applications (VBA)
	Visual Basic for Applications logoVisual Basic for Applications logo
Paradigm	Multi-paradigm
Developer	Microsoft
First appeared	1993
Stable release	7.0 (Office 2010) / 2010; 14 years ago
Typing discipline	Static/Dynamic Hybrid, Strong/Weak Hybrid
OS	Microsoft Windows, Mac OS X
License	Proprietary EULA
Influenced by
	QuickBASIC, Visual Basic

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Revision as of 15:01, 3 July 2012

Visual Basic for Applications (VBA) is an implementation of Microsoft's event-driven programming language Visual Basic 6 and its associated integrated development environment (IDE), which are built into most Microsoft Office applications. VBA enables building user defined functions, automating processes and accessing Windows API and other low-level functionality through dynamic-link libraries (DLLs). It is also built into Office for Mac applications (apart from version 2008) and other Microsoft applications such as Microsoft MapPoint and Microsoft Visio, as well as being at least partially implemented in other applications such as AutoCAD, WordPerfect and ArcGIS. It supersedes and expands on the abilities of earlier application-specific macro programming languages such as Word's WordBasic. It can be used to control many aspects of the host application, including manipulating user interface features, such as menus and toolbars, and working with custom user forms or dialog boxes. VBA can also be used to create import and export filters for various file formats, such as OpenDocument (ODF).

As its name suggests, VBA is closely related to Visual Basic and uses the Visual Basic Runtime Library, but can normally only run code within a host application rather than as a standalone program. It can, however, be used to control one application from another via OLE Automation. For example, it is used to automatically create a Word report from Excel data, which is in turn automatically collected by Excel from polled observation sensors.

VBA has the ability to use (but not create) (ActiveX/COM) DLLs, and later versions add support for class modules.

Language

Code written in VBA is compiled^[1] to a proprietary intermediate language called P-code (packed code), which the hosting applications (Access, Excel, Word, Outlook, and PowerPoint) store as a separate stream in COM Structured Storage files (e.g., .doc or .xls) independent of the document streams. The intermediate code is then executed^[1] by a virtual machine (hosted by the hosting application). Despite its resemblance to many old BASIC dialects (particularly Microsoft BASIC, from which it is indirectly derived), VBA is incompatible with any of them except Visual Basic, where source-code of VBA modules and classes can be directly imported, and which shares the same library and virtual machine. Compatibility ends with Visual Basic version 6; VBA is incompatible with Visual Basic .NET (VB.NET). VBA is proprietary to Microsoft and, apart from the COM interface, is not an open standard.

Automation

Interaction with the host application uses OLE Automation. Typically, the host application provides a type library and application programming interface (API) documentation which document how VBA programs can interact with the application. This documentation can be examined from inside the VBA development environment using its Object Browser.

VBA programs which are written to use the OLE Automation interface of one application cannot be used to automate a different application, even if that application hosts the Visual Basic runtime, because the OLE Automation interfaces will be different. For example, a VBA program written to automate Microsoft Word cannot be used with a different word processor, even if that word processor hosts VBA.

Conversely, multiple applications can be automated from the one host by creating Application objects within the VBA code. References to the different libraries must be created within the VBA client before any of the methods, objects, etc. become available to use in the application. These application objects create the OLE link to the application when they are first created. Commands to the different applications must be done explicitly through these application objects in order to work correctly.

For example: In Microsoft Access, users automatically have access to the Access library. References to the Excel, Word and Microsoft Outlook libraries can also be created. This will allow creating an application that runs a query in Access, exports the results to Excel, formats the text, then writes a mail merge document in Word that it automatically e-mails to each member of the original query through Outlook.

VBA programs can be attached to a menu button, a macro, a keyboard shortcut, or an OLE/COM event, such as the opening of a document in the application. The language also provides a user interface in the form of UserForms, which can host ActiveX controls for added functionality.

Security concerns

Like any common programming language, VBA macros can be created with malicious intent. Using VBA, most of the security features lie in the hands of the user, not the author. The VBA host application options are accessible to the user. The user who runs any document containing VBA macros can preset the software with user preferences. End-users can protect themselves from attack by disabling macros from running in an application, or only grant permission for a document to run VBA code if they are sure the source of the document can be trusted.

Named variables and user-defined functions

A common use of VBA is to add functionality that may be missing from the standard user interface. Use of VBA is made much easier by using named variables on the spreadsheet, as shown at the left. The formula for y=x² resembles Fortran or BASIC, and the Name Manager shows the definitions of column variables y and x.

Using VBA, the user can add their own functions and subroutines that refer to these named ranges. In the figure at the right, the function sq is created in the Visual Basic editor supplied with Excel, and x & y are named variables in the spreadsheet.

Subroutines

Functions themselves cannot write into the worksheet, but simply return their evaluation. However, in Microsoft Excel, subroutines can write values or text found within the subroutine directly to the spreadsheet. The figure shows the Visual Basic code for a subroutine that reads each member of the x-column (named column variable x), calculates its square, and writes this value into the corresponding y-column (also a named column variable). The y-column contains no formula because its values are calculated in the subroutine and simply written in.

Examples

This macro provides a shortcut for entering the current date in Word:

Sub EnterCurrentDate()
    Selection.InsertDateTime DateTimeFormat:="dd-MM-yy", InsertAsField:=False, _
         DateLanguage:=wdEnglishAUS, CalendarType:=wdCalendarWestern, _
         InsertAsFullWidth:=False
End Sub

VBA is useful for automating database tasks such as traversing a table:

Sub LoopTableExample

    Dim db As DAO.Database
    Dim rs As DAO.Recordset

    Set db = CurrentDb
    Set rs = db.OpenRecordset("select columnA, columnB from tableA")

    Do Until rs.EOF
         MsgBox rs!columnA & " " & rs!columnB
         rs.MoveNext
    Loop

    rs.Close
    Set db = Nothing
End Sub

VBA is useful for automating repeated actions in rows of a spreadsheet. For example, using the following code example, the built-in iterative solver Goal Seek is applied automatically to each row in a column array, avoiding repeated use of manual menu entry. Below a column variable "C_M" determines the values of another column variable "Target" in some nonlinear fashion. The built-in nonlinear solver Goal Seek is called to find the value of "C_M" that brings "Target" to value one. The subroutine is inserted into the workbook using the VBA editor and command Insert Module. It is called directly from the VBA editor, or by using a "hot key" or keyboard shortcut. Values on the spreadsheet automatically update as the rows are scanned.

Subroutines have the power to update the contents of the workbooks; functions do not - they simply report their evaluation.

The line Option Explicit is not part of the subroutine: it sets a compiler option that forces identification of all variables that have not been specified in Dim statements, which avoids difficult to detect debugging problems caused by typos. Notation ( ' ) in the following code denotes a comment, and ( _) line continuation. The code uses 'named' variables: a form of cell reference in which cells are assigned names of user choice, rather than the standard cell designation denoting specific row and column numbers. Naming is done on the worksheet via the Excel "Name Manager", or menu Insert Name: Create.

Option Explicit

Sub SetTarget()
'
' SetTarget Macro
'
   Dim J As Integer
   Dim Size As Integer
'
' On the spreadsheet, array "C_M" is a NAMED column variable
'     Its members use a row index taken as J
' Built-in function COUNT determines size of array "C_M"
'
   Size = Range("C_M").Cells.Count
'
' Set initial value of all members of array
'    C_M to 1E-06; J = row index
'
       For J = 1 To Size
           Range("C_M").Cells(J) = 0.000001
       Next J
 'Or in case of constant value
       Range("C_M") = 0.000001
'
' "Target" is another NAMED array on the spreadsheet of
'      dimension "Size"; the same size as array "C_M"
'
' Each "Target" entry in each row depends in a
'      specified way upon the value of "C_M" in that row,
'      for example, by a function such as: Target = C_M*C_M
'
' GOAL SEEK is a built-in iterative solver in Excel
'
' Call GOAL SEEK to set each "Target" member to unity: for example,
'   taking J = row index, in row J the cell named "C_M" is changed
'   by GOAL SEEK until "Target" in row J is one
'
' Syntax (aside from "for-next" details) found with macro recorder;
'      underscore "_" is line continuation
'
       For J = 1 To Size
           Range("Target").Cells(J).GoalSeek Goal := 1, _
             ChangingCell := Range("C:M").Cells(J)
       Next J
End Sub

In the example below VBA is used to get an array from a cell range, manipulate the array, and then set the values back in a different range. This works many times faster than directly setting the cell values one-by-one.

Sub CalculateSquares(rinput As Range, routput As Range)
   'Variable specifications
    Dim values() As Variant
    Dim i As Integer, N As Integer

    'Count the rows to compute
    N = rinput.Rows.Count

    'Set values array from input range.
    'Expected shape of array is (1 to N, 1 to 1)
    values = rinput.Value

    'Iterate through rows and set values
    For i = 1 To N
        values(i, 1) = values(i, 1) ^ 2
    Next i

    'Export values back into the spreadsheet by setting the
    'value property of the output range.
    routput.Value = values

End Sub

VBA can be used to create a user defined function (UDF) for use in a Microsoft Excel workbook:

Public Function BusinessDayPrior(dt As Date) As Date

    Select Case Weekday(dt, vbMonday)
        Case 1
            BusinessDayPrior = dt - 3      'Monday becomes Friday
        Case 7
            BusinessDayPrior = dt - 2      'Sunday becomes Friday
        Case Else
            BusinessDayPrior = dt - 1      'All other days become previous day
    End Select
End Function

Example of how to add an external application object (the user must have the application library referenced in the application before this):

Public Sub Example()
    Dim XLApp As Excel.Application
    Dim WDApp As Word.Application

    Set XLApp = CreateObject("Excel.Application")
    Set WDApp = CreateObject("Word.Application")

    ' ...your code here...

    XLApp.Quit
    WDApp.Quit

    Set XLApp = Nothing
    Set WDApp = Nothing
End Sub

Future

As of July 1, 2007, Microsoft no longer offers VBA distribution licenses to new customers. Microsoft intended to add .NET-based languages to the current version of VBA ever since the release of the .NET Framework,^[2] of which versions 1.0 and 1.1 included a scripting runtime technology named Script for the .NET Framework.^[3] Also, Visual Studio .NET 2002 and 2003 SDK contained a separate scripting IDE called Visual Studio for Applications (VSA) that supported VB.NET.^[4]^[5]^[6] One of its significant features was that the interfaces to the technology were also available via Active Scripting (VBScript and JScript), allowing even .NET-unaware applications to be scripted via .NET languages. However, VSA was deprecated in version 2.0 of the .NET Framework,^[6] leaving no clear upgrade path for applications desiring Active Scripting support (although "scripts" can be created in C#, VBScript, and other .NET languages, which can be compiled and executed at run-time via libraries installed as part of the standard .NET runtime).

Support for VBA in the Mac OS X version of Microsoft Office was dropped (for one version) with the release of Microsoft Office 2008 for Mac.^[7]^[8] The official reason given was that VBA relied heavily on machine code written for the PowerPC architecture, and that rewriting this code for dual PowerPC/Intel architectures would have added another 2 years to the development of the suite. However, the Office suite can be automated via AppleScript to an extent. VBA was restored in Microsoft Office for Mac 2011. Microsoft has also clearly stated that they have no plans to remove VBA from the Windows version of Office.^[9]^[10]

With Office 2010, Microsoft has introduced VBA7 which now contains a true pointer data type: LongPtr. This new data type allows referencing 64-bit address space. The 64-bit install of Office 2010 does not support common controls of MSComCtl (TabStrip, Toolbar, StatusBar, ProgressBar, TreeView, ListViews, ImageList, Slider, ImageComboBox) or MSComCt2 (Animation, UpDown, MonthView, DateTimePicker, FlatScrollBar) so legacy 32-bit code ported to 64-bit VBA code that depends on these common controls will not function. The 32-bit version of Office 2010 is unaffected by this issue.^[11] VBA7 includes no 64-bit version of the common controls, so it leaves developers with no means to migrate VBA applications to 64-bits. Microsoft suggests contacting the software vendor for 64-bit versions of VBA controls.

Visual Studio Tools for Applications (VSTA)

With the release of Visual Studio 2005, Microsoft announced Visual Studio Tools for Applications (VSTA). Independent Software Vendors may contact Microsoft through their vstainfo email address to inquire about licensing VSTA to provide their end-users with customization facilities within their application, in a similar way to VBA. However, VSTA uses the Visual Studio 2005 or Visual Studio 2008 development environment for programming against the .NET Framework.

VSTA was included in Office 2007 particularly for adding custom program code to InfoPath forms.

References

External links

A VBA Primer for mostly Microsoft Excel

[both-1] ACC: Visual/Access Basic Is Both a Compiler and an Interpreter

[2] Visual Studio for Applications

[3] Introducing Visual Studio for Applications

[4] Script happens .NET: MSDN

[5] Microsoft Takes Wraps Off VSA Development Technology

[VSA-6] VSA scripting in .NET

[7] "WWDC: Microsoft updates Universal status of Mac apps". Macworld. 2006-08-07. Retrieved 2007-05-25. {{cite web}}: External link in |publisher= (help)

[8] Office 2008 without VBA

[9] The Reports of VBA's Demise Have Been Greatly Exaggerated

[10] Clarification on VBA Support

[11] ttp://msdn.microsoft.com/en-us/library/ee691831.aspx

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