Introduction.
VBA (Visual Basic for Applications) provides several predefined data types, such as Integer, String, Date, and others, which are used to store specific types of data. For example, an Integer variable can hold numeric values ranging from -32,768 to +32,767, while a String variable stores alphanumeric values, and so on.
However, programmers can also define their own custom data types, combining multiple predefined data types into a single structure, and use them in their programs. Let’s explore this concept with a simple example.
Creating a User-Defined Type.
Open one of your existing databases or create a new one.
Open the VBA Editing Window (Alt+F11 or Tools ->Macro -> VBA Editing)
Access2007:
Select Modules from the Object drop-down list.
Double-click on an existing Module or select Create Menu.
Select the Macro- ->Modules Toolbar button to create a new Standard Module.
Copy and paste the following Code into the Module.
Public Type WagesRec
strName As String
dblGrossPay As Double
dblTaxRate As Double
dblNetPay As Double
booTaxPaid As Boolean
End Type
Public Function WagesCalc()
Dim netWages As WagesRec, strMsg As String
Dim fmt As String
With netWages
.strName = InputBox("Employee Name: ", , "")
.dblGrossPay = InputBox("Enter Gross Pay:", , 0)
.dblTaxRate = InputBox("Enter Taxrate", , 0)
.dblNetPay = .dblGrossPay - (.dblGrossPay * .dblTaxRate)
If .dblTaxRate <> 0 Then
.booTaxPaid = True
End If
'Display Record
fmt = "#,##0.00"
strMsg = "Name: " & .strName & vbCr & "Grosspay: " & Format(.dblGrossPay, fmt) & vbCr
strMsg = strMsg & "Tax Rate: " & Format(.dblTaxRate * 100, fmt) & "%" & vbCr & "Tax Amt.: " & Format(.dblGrossPay * .dblTaxRate, fmt) & vbCr
strMsg = strMsg & "Net Pay: " & Format(.dblNetPay, fmt) & vbCr & "Tax Paid: " & .booTaxPaid
MsgBox strMsg, , "WagesCalc()"
End With
End FunctionPlace the insertion point somewhere in the middle of the WagesCalc() Function and press the F5 Key to run the Code.
Key in the name of the Employee, Gross Pay, and Tax Rate Values when prompted for them.
The output display of the program is shown below:
The Type Declaration and Properties.
Let us examine the above Code. The User-defined data type declaration is made at the global area of a Standard Module within the Type WagesRec... End Type structure. WagesRec is an arbitrary name; it can be anything that you like, but it should follow the Variable naming conventions. By default, the scope of the data type is Public, i.e., we can declare a variable using the new data type in Standard Modules and Class Modules as well. When it is declared as Private, like Private Type WagesRec. . .End Type: The scope of the data type is within that module only.
The individual element's name of the new data type should also follow the normal variable naming conventions.
We have declared a Variable NetWages (you can take NetWages as an Object having several properties that can be set with values) using the new data type WagesRec in our WagesCalc() Function. Individual elements of the NetWages Variable can be addressed as a subset of that object; both separating with a dot (.) like Netwages.dblGrossPay to set its value or retrieve its contents.
We have used three InputBox statements to ask the user to input values for the Name, Grosspay, Tax Rate, calculate the Tax Value, Net Payable amount, and set the Tax Paid flag if the Tax Rate is a non-zero value.
Next part of the program, we have loaded a String Variable strMsg with the output labels and values to display them through a MsgBox.
Array Data Type Elements.
In the above Type declaration example, we have used the predefined System data types as elements. Besides that, we can declare Subscripted Elements and other User-Defined Data Types also as elements, like the following example:
Public Type MyRecord
dblIncentives(1 to 100) as double
EmployeeRec as WagesRec
End Type
In our program, let us assume that we have declared a variable with the above data type, like the following:
Dim EmployeeWages as MyRecord
Addressing the individual elements and their sub-elements will be as follows to assign values to them:
EmployeeWages.dblIncentives(1) = 5000
EmployeeWages.EmployeeRec.strName = "John Smith"
Subscripted Variable.
But the whole Data Type can be declared as a Subscripted Variable like:
Dim EmployeeWages(1 to 100) as MyRecord
Then how do we address the individual elements of the Variable?
EmployeeWages(1).dblIncentives(1) = 500
EmployeeWages(1).dblIncentives(2) = 750
EmployeeWages(1).EmployeeRec.strName = "John Smith"
EmployeeWages(1).EmployeeRec.dblGrossPay = 15000
EmployeeWages(2).dblIncentives(1) = 400
EmployeeWages(2).dblIncentives(2) = 450
EmployeeWages(2).EmployeeRec.strName = "George"
EmployeeWages(2).EmployeeRec.dblGrossPay = 17000
Sorting the Array of User-Defined Types.
We will see another example that uses subscripted user-defined data types. In this example, we will declare a new Data Type for the Employees Table from the Northwind.mdb sample database. We will load a few field values of the Employees Table into our User-Defined Subscripted Variable, sort the Names in memory, and print the output in the Debug Window.
1. Import the Employees Table from C:\Program Files\Microsoft Office\Office11\Samples\Northwind.mdb the sample database,
2. Copy and paste the following VBA Code into a new Standard Module and save the Module:
Type PersonalRecord
strFirstName As String
strLastName As String
dtDB As Date
strAddress As String
strCity As String
strPostalCode As String
End Type
Public Function ReadSort()
Dim PRec() As PersonalRecord, PRecX As PersonalRecord
Dim db As Database, rst As Recordset, recCount As Long
Dim J As Long, k As Long, h As Long
Set db = CurrentDb
Set rst = db.OpenRecordset("Employees", dbOpenDynaset)
rst.MoveLast
recCount = rst.RecordCount
ReDim PRec(1 To recCount) As PersonalRecord
rst.MoveFirst
J = 0
'Load Employee Records into Userdefined Variable Array
Do While Not rst.EOF
J = J + 1
With rst
PRec(J).strFirstName = ![FirstName]
PRec(J).strLastName = ![LastName]
PRec(J).dtDB = ![BirthDate]
PRec(J).strAddress = ![Address]
PRec(J).strCity = ![City]
PRec(J).strPostalCode = ![PostalCode]
End With
rst.MoveNext
Loop
rst.Close
Debug.Print "Before Sorting"
Debug.Print "--------------"
DisplayRoutine PRec()
'Bubble Sort on FirstName
For k = 1 To J - 1
For h = k + 1 To J
If PRec(h).strFirstName < PRec(k).strFirstName Then
'Swap the Records
'move the first record to temporary storage area
PRecX.strFirstName = PRec(k).strFirstName
PRecX.strLastName = PRec(k).strLastName
PRecX.dtDB = PRec(k).dtDB
PRecX.strAddress = PRec(k).strAddress
PRecX.strCity = PRec(k).strCity
PRecX.strPostalCode = PRec(k).strPostalCode
'move the second record to replace the first
PRec(k).strFirstName = PRec(h).strFirstName
PRec(k).strLastName = PRec(h).strLastName
PRec(k).dtDB = PRec(h).dtDB
PRec(k).strAddress = PRec(h).strAddress
PRec(k).strCity = PRec(h).strCity
PRec(k).strPostalCode = PRec(h).strPostalCode
'move the from temporary storage to replace the second record
PRec(h).strFirstName = PRecX.strFirstName
PRec(h).strLastName = PRecX.strLastName
PRec(h).dtDB = PRecX.dtDB
PRec(h).strAddress = PRecX.strAddress
PRec(h).strCity = PRecX.strCity
PRec(h).strPostalCode = PRecX.strPostalCode
End If
Next h
Next k
Debug.Print "After Sorting"
Debug.Print "--------------"
DisplayRoutine PRec()
End Function
Public Function DisplayRoutine(ByRef getRecord() As PersonalRecord)
Dim RecordCount As Long, J As Long
RecordCount = UBound(getRecord)
For J = 1 To RecordCount
Debug.Print getRecord(J).strFirstName, getRecord(J).strLastName, getRecord(J).dtDB
Next
Debug.Print
Debug.Print
End Function3. Place the insertion point in the middle of the Module and press F5 to run the Code.
4. Press Ctrl+G to display the Debug Window, and you will find the following output printed there:
Before Sorting
--------------
Nancy Davolio 08/09/1968
Andrew Fuller 19/02/1952
Janet Leverling 30/08/1963
Margaret Peacock 19/09/1958
Steven Buchanan 04/03/1955
Michael Suyama 02/07/1963
Robert King 29/05/1960
Laura Callahan 09/01/1958
Anne Dodsworth 02/07/1969
After Sorting
--------------
Andrew Fuller 19/02/1952
Anne Dodsworth 02/07/1969
Janet Leverling 30/08/1963
Laura Callahan 09/01/1958
Margaret Peacock 19/09/1958
Michael Suyama 02/07/1963
Nancy Davolio 08/09/1968
Robert King 29/05/1960
Steven Buchanan 04/03/1955
How it Works.
At the beginning of the program, we opened the Employees Table, read the count of records in the Table, and accordingly, we re-dimensioned the user-defined variable PersonalRecord to reserve enough space to hold all the Employees records.
Next, we opened the Employees Table and loaded all the employees' data into the array.
We have sent a list of the unsorted data in the Debug Window.
The data is sorted in Ascending Order on FirstName in memory using the bubble sort method.
The sorted employee records are listed in the Debug Window again.
Tip: You can change the sorting order to descending order by changing the logical operator < to > in the following statement:
If PRec(h).strFirstName < PRec(k).strFirstName Then
If PRec(h).strFirstName > PRec(k).strFirstName Then
As you can see, the data printing Routine is a separate Function Display Routine() and we have passed the whole Array of records to this program twice to print its contents into the Debug Window.
Download Demo BudgetDemo.zip
