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VBA - Excel

VBA - Excel. VBA is Visual Basic for Applications The goal is to demonstrate how VBA can be used to leverage the power of Excel VBA syntax and usage the Excel VB programming environment the Excel object model an application. VBA - Excel. What advantage is there in using VBA

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VBA - Excel

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  1. VBA - Excel • VBA is Visual Basic for Applications • The goal is to demonstrate how VBA can be used to leverage the power of Excel • VBA syntax and usage • the Excel VB programming environment • the Excel object model • an application

  2. VBA - Excel • What advantage is there in using VBA • extend Excel – new functions • makes it possible to use the Execl GUI environment • makes it possible to respond to events (mouse, …) • makes Windows programming API accessible • Excel can be used to control Automation servers (other software components that expose an API through COM) • by understanding how to use the Excel object model with VBA it is a small step to using Excel as an Automation server (controlled by other program)

  3. VBA - Excel • In order to run VBA code your security settings must be properly set • Tools | Macro | Security… • At least Medium security must be set – each macro will require user verification to run • Signed code can be run in all cases

  4. VBA – The Basics • Data types • Integer 2 byte integer • Long 4 byte integer • Single 4 byte floating point • Double 8 byte floating point • Currency 8 byte real • String upto 64K characters • Byte 1 byte • Boolean 2 byte true or false • Date 8 bytes • Object 4 bytes – an object reference • Variant 16 bytes + 1 byte / character

  5. VBA – The Basics • The variant data type is special – a variant can hold any type of data • A variable declared as variant (the default) can hold anything • The actual type of the data is kept in the data • It adds flexibility but at a cost – it requires more processing at compute time to determine what it is and how to handle it

  6. VBA – The Basics • Variables • must start with a letter • can contain _ and numbers • cannot exceed 255 characters in length • Within a procedure declare a variable using • If a variable is not declared it will be created when used, the type will be Variant • Use Option Explicit in the declarations section to require declaration of variables • VBA variables have scope restrictions • variables declared in a procedure are local to that procedure • variables declared in a module can be public or private Dim variable Dim variable As type

  7. VBA – The Basics • String variables • The first form is variable length • The second form is limited to 50 characters • the variable will be space filled if string is < 50 characters • the string will be truncated if the contents are > 50 characters • the Trim and RTrim functions are useful for working with fixed length strings • Boolean variables contain either True or False Dim variable As String Dim variable As String * 50

  8. VBA – The Basics • The Object type is used to store the address (a reference) of an object • this form can be used for any object • this is referred to as late-binding, the object types are checked at runtime (slower) • The declaration of a specific object is • this form will only store Excel Worksheet objects, an attempt to put anything else into it will result in an error • this is referred to as early-binding, the object types are checked at compile time (faster) Dim variable As Object Dim variable As Worksheet

  9. VBA – The Basics • Arrays are declared using • Arrays can be multidimensional • The lower bound starts at zero • can explicitly specify lower bound • can use Option Base command to reset to something other than 0 • The last form above is a dynamic array – it must be dimensioned using ReDim before it can be used • Use ReDim Preserve to retain any existing entries in array - only the upper bound of array can be changed Dim A (1 To 10) As Double Dim B (1 To 10, 1 To 10) As Double Dim C (4,4,4) As Integer Dim D () As Double Option Base 1

  10. VBA – The Basics • Constants are declared using • Constants have the same scope limitations as variables Const pi = 3.14159 Const pi As Double = 3.14159

  11. VBA – The Basics • User defined data types • can only be defined in the declarations section of a Module • can be Public or Private in scope • Declare variable with this type • Referencing fields Public Type SystemInfo CPU As Variant Memory As Long ColorBits As Integer Cost As Currency PurchaseDate As Date End Type Dim MySystem As SystemInfo MySystem.CPU = “Pentium” If MySystem.PurchaseDate > #1/1/2006# Then … End If

  12. VBA – The Basics • Watch out for • it is equivalent to Dim a, b, c As Integer Dim a As Variant Dim b As Variant Dim c As Integer

  13. VBA – The Basics • Objects • VBA can use pre-defined objects – such as intrinsic Excel objects • VBA can create user-defined objects – Class Modules • Declaring a variable to contain an object • the first form declares that the variable will contain a reference to an object of the named class • the second form declares the variable then creates an instance of the class • To instantiate a class Dim variable As class Dim variable As New class Set variable = New class

  14. VBA – The Basics • Objects • To declare a variable that will refer to an instance of the Excel Worksheet class • To put a reference into it • This fragment will print the name of the worksheet “Sheet1” Dim ws1 As Worksheet Set ws1 = Worksheets(“Sheet1”) Dim ws1 As Worksheet Set ws1 = Worksheets("sheet1") Debug.Print ws1.Name

  15. VBA – The Basics • Objects - Collections • There is a special form of objects known as Collections • They contain references to other objects and collections • It is the mechanism by which the object hierarchy is defined • By convention, collection names are usually plural • Workbooks – list of Workbook objects • Worksheets – list of Worksheet objects • Range – list of objects that represent cells, columns, rows • The following example iterates through Workbooks collection For Each ws In Worksheets Debug.Print ws.Name Next

  16. VBA – The Basics • Statements • VBA implements common programming statements • logical statements • looping statements • expressions

  17. VBA – The Basics • Logical statements • The If Then Else statement is the basic logic test If a>10 Then … End If If a>10 Then … Else … End If If a>10 Then … ElseIf a<0 Then … Else … End If

  18. VBA – The Basics • Logical statements • The Select statement can be used to replace a multi-way if statement Select Case expression Case expr1 … Case expr2 … Case Else … End Select

  19. VBA – The Basics • Loop statements • Various Do loop forms Do Until expr … Loop Do While expr … Loop Do … Loop Until expr Do … Loop While expr

  20. VBA – The Basics • Loop statements • A common For loop For i=1 To 10 Debug.print i Next i For i=1 To 10 Step 2 Debug.print i Next i

  21. VBA – The Basics • Loop statements • Another For loop • Commonly used to iterate through collections For Each element In group … Next element For Each ws In Worksheets Debug.Print ws.Name Next

  22. VBA – The Basics • Procedures • Procedures in VBA are either Macros or Functions • a macro does not return a value • a function will return a value • Property functions (Get and Let) are used in Class Modules to provide access to private properties Sub Name() … End Sub Function Name() As Double … End Sub

  23. VBA – The Basics • Dealing with runtime errors • The On Error statement will trap errors • The error name is a label in the code • In the error code a Resume statement will cause the statement that caused the error to be executed again • In the error code a Resume Next statement will restart execution on the statement after the one that caused the error … On Error GoTo label … On Error GoTo check … check: …

  24. VBA – Programming Environment • Excel (all Office components) have a VBA programming environment, VBIDE • It consists of • the Visual Basic Editor • an Object Browser • debugging support • These are accessed from the Excel menu • There is also a set of CHM files that document the components and object models of Office (for version 10) • the Excel file is named VBAXL10.CHM • XLMAIN10.CHM is the main help file for Excel and contains VBAXL10.CHM within it • each version of Office has its own set of files • http://www.ae.gatech.edu/classes/ae6382/documents/MS_Scripting/Office10/

  25. VBA – Programming Environment • To start the Visual Basic Editor from Excel select • Tools | Macro | Visual Basic Editor

  26. VBA – Programming Environment • Once in the VB Editor – to start the Object Browser select • View | Object Browser

  27. VBA – Programming Environment • In the Object Browser to select only the Excel objects use the pull down menu at the upper left

  28. VBA – Programming Environment • To view information on the Worksheet object and its Name property

  29. VBA – Programming Environment • The usual way to create code is to double-click on one of the Worksheet or Workbook objects in the Project Explorer and enter the code.

  30. VBA – Programming Environment • By using the menu item Insert it is possible to add other types of procedure containers • forms (GUI) • modules for library-like procedures • class modules for defining classes

  31. VBA – Excel Objects • Excel exposes all of its functionality through objects • These are directly accessible to the VBA programmer • They are also visible to other applications through COM Automation • matlab • scripting languages • other Office components

  32. VBA – Excel Objects • The top level object is the Workbook. • A workbook corresponds to an open XLS file • Each Workbook object is kept in the Workbooks collection • To open a workbook file use • Dim wb = Workbooks.Open(“filename) • To close a workbook use the Close method on the workbook object or the Workbooks entry • Other methods for use with Workbooks are Save and SaveAs

  33. VBA – Excel Objects • The Worksheet corresponds to a Sheet • Each Worksheet object is kept in the Worksheets collection • To add a single new Worksheet • Dim ws = Worksheets.Add(count:=1) • ws.Visible = False will hide the sheet • ws.Delete will delete the sheet • Worksheets(“Sheet1”).Delete will delete a sheet

  34. VBA – Excel Objects • The Range object (collection) corresponds to a set of cells • To set a value into a cell • Worksheets(“Sheet1”).Range(“A5”).Value = 3.14159

  35. VBA – An Example • An example found on the Internet • http://www.ae.gatech.edu/classes/ae6382/samples/vba/

  36. VBA – An Example • A view from the Visual Basic Editor

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