VBA - Excel
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VBA is Visual Basic for Applications
The goal is to demonstrate how VBA can be used to leverage the
power of Excel
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VBA syntax and usage
the Excel VB programming environment
the Excel object model
an application
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VBA - Excel
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What advantage is there in using VBA
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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)
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VBA - Excel
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In order to run VBA code your security settings must be properly set
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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
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VBA – The Basics
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Data types
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Integer
Long
Single
Double
Currency
String
Byte
Boolean
Date
Object
Variant
2 byte integer
4 byte integer
4 byte floating point
8 byte floating point
8 byte real
upto 64K characters
1 byte
2 byte true or false
8 bytes
4 bytes – an object reference
16 bytes + 1 byte / character
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VBA – The Basics
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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
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VBA – The Basics
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Variables
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must start with a letter
can contain _ and numbers
cannot exceed 255 characters in length
Within a procedure declare a variable using
Dim variable
Dim variable As type
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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
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variables declared in a procedure are local to that procedure
variables declared in a module can be public or private
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VBA – The Basics
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String variables
Dim variable As String
Dim variable As String * 50
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The first form is variable length
The second form is limited to 50 characters
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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
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VBA – The Basics
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The Object type is used to store the address (a reference) of an
object
Dim variable As Object
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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
Dim variable As Worksheet
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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)
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VBA – The Basics
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Arrays are declared using
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
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Arrays can be multidimensional
The lower bound starts at zero
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can explicitly specify lower bound
can use Option Base command to reset to something other than 0
Option Base 1
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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
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VBA – The Basics
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Constants are declared using
Const pi = 3.14159
Const pi As Double = 3.14159
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Constants have the same scope limitations as variables
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VBA – The Basics
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User defined data types
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can only be defined in the declarations section of a Module
can be Public or Private in scope
Public Type SystemInfo
CPU As Variant
Memory As Long
ColorBits As Integer
Cost As Currency
PurchaseDate As Date
End Type
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Declare variable with this type
Dim MySystem As SystemInfo
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Referencing fields
MySystem.CPU = “Pentium”
If MySystem.PurchaseDate > #1/1/2006# Then
…
End If
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VBA – The Basics
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Watch out for
Dim a, b, c As Integer
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it is equivalent to
Dim a As Variant
Dim b As Variant
Dim c As Integer
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VBA – The Basics
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Objects
VBA can use pre-defined objects – such as intrinsic Excel objects
VBA can create user-defined objects – Class Modules
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Declaring a variable to contain an object
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Dim variable As class
Dim variable As New class
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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
Set variable = New class
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VBA – The Basics
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Objects
To declare a variable that will refer to an instance of the Excel
Worksheet class
Dim ws1 As Worksheet
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To put a reference into it
Set ws1 = Worksheets(“Sheet1”)
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This fragment will print the name of the worksheet “Sheet1”
Dim ws1 As Worksheet
Set ws1 = Worksheets("sheet1")
Debug.Print ws1.Name
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VBA – The Basics
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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
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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
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VBA – The Basics
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Statements
VBA implements common programming statements
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logical statements
looping statements
expressions
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VBA – The Basics
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Logical statements
The If Then Else statement is the basic logic test
If a>10 Then
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End If
If a>10 Then
…
Else
…
End If
If a>10 Then
…
ElseIf a<0 Then
…
Else
…
End If
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VBA – The Basics
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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
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VBA – The Basics
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Loop statements
Various Do loop forms
Do While expr
Do Until expr
…
…
Loop
Loop
Do
Do
…
Loop While expr
…
Loop Until expr
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VBA – The Basics
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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
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VBA – The Basics
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Loop statements
Another For loop
For Each element In group
…
Next element
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Commonly used to iterate through collections
For Each ws In Worksheets
Debug.Print ws.Name
Next
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VBA – The Basics
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Procedures
Procedures in VBA are either Macros or Functions
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a macro does not return a value
Sub Name()
…
End Sub
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a function will return a value
Function Name() As Double
…
End Sub
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Property functions (Get and Let) are used in Class Modules to provide
access to private properties
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VBA – The Basics
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Dealing with runtime errors
The On Error statement will trap errors
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On Error GoTo label
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The error name is a label in the code
…
On Error GoTo check
…
check:
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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
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VBA – Programming Environment
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Excel (all Office components) have a VBA programming
environment, VBIDE
It consists of
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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)
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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
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http://www.ae.gatech.edu/classes/ae6382/documents/MS_Scripting/Office10/
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VBA – Programming Environment
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To start the Visual Basic Editor
from Excel select
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Tools | Macro | Visual Basic Editor
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VBA – Programming Environment
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Once in the VB Editor – to start
the Object Browser select
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View | Object Browser
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VBA – Programming Environment
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In the Object Browser to select
only the Excel objects use the
pull down menu at the upper
left
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VBA – Programming Environment
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To view information on the
Worksheet object and its
Name property
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VBA – Programming Environment
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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.
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VBA – Programming Environment
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By using the menu item Insert
it is possible to add other types
of procedure containers
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forms (GUI)
modules for library-like
procedures
class modules for defining
classes
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VBA – Excel Objects
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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
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matlab
scripting languages
other Office components
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VBA – Excel Objects
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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
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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
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VBA – Excel Objects
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The Worksheet corresponds to a Sheet
Each Worksheet object is kept in the Worksheets collection
To add a single new Worksheet
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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
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VBA – Excel Objects
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The Range object (collection) corresponds to a set of cells
To set a value into a cell
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Worksheets(“Sheet1”).Range(“A5”).Value = 3.14159
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VBA – An Example
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An example found on the Internet
http://www.ae.gatech.edu/classes/ae6382/samples/vba/
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VBA – An Example
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A view from the Visual Basic
Editor
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Visual Basic for Applications