On this class sheet, we can specify the members (properties and methods) that the objects created using this template will have.

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Brian Underwood
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1 Classes A class is a template for creating our own objects. In Excel VBA a class comes in the form of a special sheet which we can inset into our program. On this class sheet, we can specify the members (properties and methods) that the objects created using this template will have. We are then able to utilize the dot operator notation when accessing these members as we already do with Excel objects (e.g. Range("a1").Value = 3 (property) and Range("a1").Clear (method)). After the code in the class has been fully tested, this class sheet could then potentially be imported to another Excel project. This encapsulated code could then be utilized in the new project without regard for the internal workings of the code. We could then only need to concern ourselves what it does. Let us create a class in Excel. 1. Chapter title 1

2 With our new class sheet highlighted, choose Property Window from the VBE

2 To make a class In Excel VBA, a class takes the form of a special sheet - a class module. 1 From the VBE, choose Insert, Class Module. 2 With our new class sheet highlighted, choose Property Window from the VBE menu. (It won t do to right-click on the class sheet to choose properties!) 2 Title in easy steps

To do this we create two public variables. (Recall that a Public variable will be accessible from outside the sheet).

3 Creating properties 3 Change the Name property to clsemp. The name of the class module is most significant. We will use it to create new objects as we shall soon see. We want our class to have two properties. SurName and Pay. To do this we create two public variables. (Recall that a Public variable will be accessible from outside the sheet). 1 Double-click on the class in Project Explorer to open the class sheet (if it is not already open) and type the declarations shown. 1. Chapter title 3

2 Place a button on the worksheet and double-click.. We will declare our object emp1 in the General Declarations which will therefore be available throughout the whole of this sheet.

4 2 Place a button on the worksheet and double-click.. We will declare our object emp1 in the General Declarations which will therefore be available throughout the whole of this sheet. Note that as we start to write the code as shown our class Name (clsemp) appears in IntelliSense. 3 Continue typing as shown. Suggestions for our properties also appear. 4 Complete the code which creates a new object and assigns values to its Properties. 4 Title in easy steps

5 5 In order to test that the property values, place another command button on the worksheet with the code below to display the values of the properties. 6 Private Sub CommandButton2_Click() MsgBox emp1.surname MsgBox emp1.salary End Sub Click CommandButon1 to write to the properties and then click CommandButon2 to read the properties. Message boxes should appear which successively display the respective property values. We have just made two properties by delaring two Public variables. A more sophisticated way of creating properties is to write Property Let and Property Get procedures in the class. For one thing, this allows us to respond differently in the class depending on whether it is a Let (write) or a Get (Read). Once again the Help is to be recommended for further details. 1. Chapter title 5

6 Creating a method This is achieved by writing a Public function in the class. 2 1 Option Explicit Public SurName As String Public Salary As Single Public Function Pay() As Single Pay = Salary / 52 End Function Return to the class sheet by double-clicking on it in the Project Explorer and and include the function shown. Place a third command button on the worksheet and include this code. Private Sub CommandButton3_Click() MsgBox emp1.pay End Sub 3 Click CommandButton 1 to write to the two properties and then click CommandButton 3 to call the Pay method which uses to value of the Salary property to calculate the weekly pay. Summary: The example given above serves only to introduce the concept of a class and the objects that can be created from a class. Classs are of enormous importance in the contempory programming environment but this may be understandably difficult to appreciate given that the example above could perhaps just as easily be written using convential functions. VB.Net for example, relies heavily on classes, even to be able to write the very simplest of programs and to that end, it is of advantage to have some basic understanding of these concepts before proceeding to learn to develop in such a language. 6 Title in easy steps

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