chapter 7: sub and function procedures programming with microsoft visual basic.net, second edition

Chapter 7: Sub and Function Procedures

Programming with Microsoft Visual Basic .NET, Second Edition

Programming with Microsoft Visual Basic .NET, Second Edition 2

Creating Sub and Function Procedures

Lesson A Objectives• Explain the difference between a Sub procedure

and a Function procedure

• Create a procedure that receives information passed to it

• Explain the difference between passing data by value and by reference

• Create a Function procedure


Procedures

• A procedure is a block of program code that performs a specific task

• Procedures in Visual Basic .NET can be either Sub procedures or Function procedures

– Sub procedures do not return a value

– Function procedures return a value after performing their assigned task


Sub Procedures

• Event procedures

– Called by Visual Basic .NET in response to an event

– Every event procedure has at least two parameters

• sender: the object that raised the event

• e: information about the object


Sub Procedures (continued)

• User-defined procedures

– You must call explicitly

– You can define parameters


Including Parameters in a User-Defined Sub Procedure

Figure 7-2: Syntax for creating a user-defined Sub procedure


Including Parameters in a User-Defined Sub Procedure (continued)

• User-defined Sub procedures have both a procedure header and procedure footer

• You use the keyword Private to indicate that only the procedures in the current form can access the procedure

• You use the keyword Public when you want to allow unlimited access to the procedure

• The Sub keyword identifies the procedure as a Sub procedure


Including Parameters in a User-Defined Sub Procedure (continued)

• parameterlist

– Lists the data type and name of memory locations used by the procedure to store the information passed to it

– Specifies how each item of information is passed: either by value or by reference

• The procedure footer for a Sub procedure is always End Sub


Passing Variables

• Passing by value: makes a copy of the data

– Use ByVal before the parameter name

– This is the default if you do not specify

• Passing by reference: passes the address of the data

– Use ByRef before the parameter name


Passing Variables (continued)

Figure 7-3: Examples of passing variables by value



Figure 7-3: Examples of passing variables by value (continued)



Figure 7-4: Examples of passing variables by reference



Figure 7-4: Examples of passing variables by reference (continued)


Function Procedures

• Function procedure

– A block of code that performs a specific task

– Typically referred to as a function

• You can create your own functions, referred to as user-defined functions

• The Return statement alerts the computer that the function has completed its task and ends the function after returning the value of its expression


Function Procedures (continued)

Figure 7-6: User-defined function syntax and example


Using a List Box ControlLesson B Objectives

• Add a list box to a form

• Add items to a list box

• Sort the contents of a list box

• Select a list box item from code


Using a List Box ControlLesson B Objectives (continued)

• Determine the selected item in a list box

• Round a number

• Code a list box’s SelectedValueChanged event


Completing the Payroll Application’s User Interface

• The payroll application should allow Mr. Williams to enter an employee’s:

– Name

– Hours worked

– Rate of pay

– Marital status (either “Married” or “Single”)

– Number of withholding allowances


Completing the Payroll Application’s User Interface (continued)

• The application should calculate the employee’s:

– Weekly gross pay

– Federal withholding tax (FWT)

– Social Security and Medicare (FICA) tax

– Net pay


Adding a List Box to a Form

• Use a list box control to display a list of choices from which the user can select zero choices, one choice, or more than one choice

• The number of choices the user is allowed to select is controlled by the list box control’s SelectionMode property

• The Windows standard for list boxes is to display a minimum of three selections and a maximum of eight selections at a time


Adding Items to a List Box

• The items in a list box belong to a collection called the Items collection

– The first item in the Items collection appears as the first item in the list box

– The second item in the Items collection appears as the second item in the list box, and so on

– The first item has an index of zero

– The second item has an index of one, and so on


Adding Items to a List Box (continued)

• Use the Items collection’s Add method to specify the items you want displayed in a list box control

• When you use the Add method to add an item to a list box, the position of the item in the list depends on the value stored in the list box’s Sorted property


The SelectedItem and SelectedIndex Properties

• A list box’s SelectItem property and SelectedIndex property can be used both to:

– Determine the item selected in the list box

– Select a list box item from code


The SelectedItem and SelectedIndex Properties

(continued)• The selected item is also called the default list

box item

– Should be either the most used selection

– Or, if all of the selections are used fairly equally, the first selection in the list


Coding the uiCalculateButton Click Event Procedure

Figure 7-18: Pseudocode for the uiCalculateButton control’s Click event procedure


Coding the GetFwtTax Function

• The amount of federal withholding text (FWT) to deduct from an employee’s weekly gross pay is based on the employee’s:

– Filing status: single (including head of household) or married

– Weekly taxable wages


Coding the GetFwtTax Function (continued)

• To calculate the federal withholding tax you need to know the employee’s:

– Gross pay amount

– Marital status

– Number of withholding allowances



Figure 7-23: Pseudocode for the GetFwtTax function



Figure 7-23: Pseudocode for the GetFwtTax function (continued)


Completing the uiCalculateButton’s Click Event Procedure

• You can call the GetFwtTax function from the uiCalculateButton’s Click event procedure


Clearing the Contents of the Label Controls

• The label controls should be cleared when the SelectedValueChanged event occurs for one of the list boxes in the interface

• A list box’s SelectedValueChanged event occurs each time a different value is selected in the list box


Completing the Payroll ApplicationLesson C Objectives

• Add an existing form to a solution

• Add a new module to a solution

• Code the Sub Main procedure

• Create an instance of a form

• Display a form object using the ShowDialog method


Adding an Existing Form to a Solution

• The copyright screen for Interlocking Software Company is to be the splash screen for each custom application created by the company

• The copyright screen identifies the application’s author and copyright year and includes the Interlocking Software Company logo


Adding an Existing Form to a Solution (continued)

Figure 7-30: Copyright form


Coding the Sub Main Procedure

• Sub Main is a special procedure in Visual Basic .NET that can be declared as the “starting point” for an application

• You can tell the computer to process the Sub Main procedure automatically when an application is started


Coding the Sub Main Procedure (continued)

• You enter the Sub Main procedure in a module

• A module is a file that contains code that is not associated with any specific object in the interface


Creating an Instance of a Form

• A class definition (or class) specifies the attributes and behaviors of an object

• When an application is started, Visual Basic .NET automatically processes the code contained in the Startup object

• If the Sub Main procedure is the Startup object, neither the CopyrightForm class definition nor the PayrollForm class definition will be processed automatically


Creating an Instance of a Form (continued)

• To allow the payroll application to display the forms associated with the CopyrightForm and the PayrollForm classes, the Sub Main procedure will need to:

– Instruct the computer to create the objects

– Instruct the computer to display the objects on the screen


Creating an Instance of a Form (continued)

• Syntax used to instruct the computer to create an object from a class: Dim variablename As New classname


Using a Form Object’s Show Dialog Method

• The form object’s ShowDialog method allows you to display a form object on the screen

• The syntax of the ShowDialog method is: form.ShowDialog()


Summary

• To pass a variable by value to a procedure, include the keyword ByVal before the parameter name in the procedure header’s parameterlist

• To pass a variable by reference, include the keyword ByRef before the parameter name in the procedure header’s parameterlist

• To add items to a list box, use the Items collection’s Add method


Summary (continued)

• To determine the item selected in a list box, or to select a list box item from code, set the list box’s SelectedItem property or its SelectedIndex property

• To process code when a different value is selected in a list box, enter the code in either the list box’s SelectedValueChanged or SelectedIndexChanged event procedure


Summary (continued)

• To add an existing item to an application, click File on the menu bar then click Add Existing Item

• To create an instance of an object from a class, use the syntax: Dim variablename As New classname

• To display a form object on the screen, use the form object’s ShowDialog method, whose syntax is: form.ShowDialog()

chapter 7: sub and function procedures programming with microsoft visual basic.net, second edition

Documents

sub slide

microsoft visual

function procedure slide

edition slide

userdefined sub procedures

procedure footer

value slide

passing variables