chapter seven sub and function procedures programming with microsoft visual basic 2010 5 th edition

Chapter SevenSub and Function

Procedures

Programming with Microsoft Visual Basic 2010

5th Edition

Programming with Microsoft Visual Basic 2010, 5th Edition

Previewing Harvey Industries Application

2

Open the Harvey.exe file The Harvey Industries application

calculates payroll for an employee

Figure 7-1 Interface showing the payroll calculations


Lesson A Objectives

3

After studying Lesson A, you should be able to:

Explain the difference between a Sub procedure and a Function procedure

Create a procedure that receives information passed to it

Create a Function procedureExplain the difference between passing

data by value and passing data by reference


More About Sub Procedures

4

ProcedureA block of program code that performs

specific taskTwo types of Sub procedures in Visual Basic

Event procedureProcedure associated with specific object and event

Independent Sub procedureIndependent of any object and eventProcessed only when called (invoked)


Passing Variables

5

VariablesHave both value and unique address

Passing by valuePasses a copy of the variable’s value

Passing by referencePasses a variable’s address


Passing Variables by Value

6

Provides only the contents of variable to receiving procedure (called procedure)

How to pass by value:Include keyword ByVal before parameter

Reasons to pass by value:Procedure needs to know the contents of

variableProcedure does not need to change original

value( 此變數只會出現在 assignment statement 右邊 )

By default, Visual Basic passes by value

example


Figure 7-5 ShowMsg procedure and btnDisplay Click event procedure7

( 定義程序時的參數 )

( 引用程序時的參數 )


Passing Variables by Reference

8

Provides the address of variable to receiving procedureAddress : memory locationReceiving procedure can thus change the value

of the variableReason to pass by reference

Procedure needs to change variable’s contents( 此變數會出現在 assignment statement 左邊，異動值傳回呼叫的程式 )

How to pass by referenceInclude keyword ByRef before parameter

example


Figure 7-8 CalcGrossPay procedure and btnCalc control’s Click event procedure

9

43.0

7.75

lstHours lstRate


Passing Variables by Reference (cont’d.)

10

Figure 7-9 Argument values before the Call CalcGrossPay statement is processed

program

Programming with Microsoft Visual Basic 2010, 5th Edition11

Figure 7-10 Argument and parameter values after the Call statement and CalcGrossPay procedure header are processed

alias

program

(Called by ByVal)

(Called by ByRef)


Figure 7-11 Argument and parameter values after the first statement in the CalcGrossPay procedure is processed

program


Figure 7-12 Argument and parameter values after the statement in the selection structure’s true path is processed

program


Figure 7-13 Argument and parameter values after the CalcGrossPay procedure ends

program


Function Procedures

15

Function procedureA block of code that performs specific taskReturns a value after completing its task

Visual Basic provides built-in functionsCan also create your own functions

As datatype in header indicates return type of data

Return expression type must agree with As datatype

Syntax & example


Figure 7-14 Function procedure syntax, examples, and steps


Invoking Function Procedures

17

Figure 7-15 Examples of invoking the GetNewPrice function


Figure 7-16 CalcGrossPay function and btnCalc control’s Click event procedure

Sub procedure方式


Lesson A Summary

19

Two types of Sub proceduresEvent and independent

Function: Performs task and returns a valueIndependent procedures and functions

Called from application’s code using Call statement

Pass by valueSend a copy of variable’s contents to procedure

or function Pass by reference

Send variable’s address to procedure or function


Lesson B Objectives

20

After studying Lesson B, you should be able to:

Include a combo box in an interfaceAdd items to a combo boxSelect a combo box item from codeDetermine the item either selected or

entered in a combo boxCode a combo box’s TextChanged event

procedure


Including a Combo Box in an Interface

21

Combo boxAllows user to select from a number of

choicesAllows user to type an entry not on listCan save space on form

List box does not share features two and three

DropDownStyle propertyValues: Simple, DropDown (default),

DropDownList

comparison


Including a Combo Box in an Interface

22

Figure 7-19 Examples of the combo box styles

Program for this UI

cboName

cboCity cboState


Figure 7-20 Code associated with the combo boxes in Figure 7-19


Including a Combo Box in an Interface (cont’d.)

24

To process code when Text property changesUse TextChanged event procedure

Use Item collection’s Add method to add itemOther properties of combo box

Sorted: Sorts items in dictionary orderSelectedIndex: Used to select item in list portionSelectedItem: Contains value of item selectedText: Contains the value that appears in text

portionUse label control to provide keyboard access

to the combo boxexam

ple


Including a Combo Box in an Interface (cont’d.)

25

Figure 7-22 Gross pay amount shown in the interface


Lesson B Summary

26

Use ComboBox tool to add combo box to a formSpecify style of combo box using DropDownStyle

propertyUse Items collection’s Add method to add items to

Combo boxUse combo box’s Sorted property to sort items in

combo’s listEnter code in combo box’s TextChanged event

procedureTo process code when Text property changes

Usage of SelectedIndex, SelectedItem, or Text property:To select combo box item from codeTo determine item that was selected


Lesson C Objectives

27

After studying Lesson C, you should be able to:

Prevent a form from closingRound a number


Creating Harvey Industries Application

28

Application objective is to calculate:Employee’s weekly gross and net pay ( 初步薪

資與淨薪資 )Federal withholding tax (FWT)Social Security and Medicare (FICA) taxNet pay


Coding FormClosing Event Procedure

29

FormClosing eventOccurs when form is about to be closed because:

Computer processes Me.Close() statement User clicks Close button on form’s title bar

Typical functions of FormClosing event procedureVerifying that user wants to close applicationTaking appropriate action based on user’s

responseTo prevent closing

Set Cancel property of FormClosing procedure’s e parameter to true


Coding the FormClosing Event Procedure

30

Figure 7-27 Pseudocode for the FormClosing event procedure

result


Coding the FormClosing Event Procedure (cont’d.)

31

Figure 7-28 Message box displayed by the code in the FormClosing event procedure

實作練習在 429~430 頁


Coding btnCalc Control’s Click Event

32

Figure 7-29 Pseudocode for the btnCalc control’s Click event procedure


UI


Creating the GetFwt Function

33

GetFwt function emulates FWT table lookupDetermining federal withholding tax (FWT)

Evaluate weekly taxable wages ( 可稅週薪 ) and filing status

Use data to look up FWT in special FWT tables

How to calculate weekly taxable wages Multiply number of withholding allowances

by $70.19Subtract this result from weekly gross pay

pseudocode


Creating the GetFwt Function (cont’d.)

34

Figure 7-35 Pseudocode for the GetFwt function


Creating the GetFwt Function (Married)

35

Figure 7-33 FWT calculations for a married ( 已婚的 ) taxpayer whose weekly taxable wages are $388.46


Creating the GetFwt Function (Single)

36

Figure 7-34 FWT calculations for a single ( 單身的 ) taxpayer whose weekly taxable wages are $600


GetFwt Function Header and Footer

37

Figure 7-36 GetFwt function header and footer



Completing the btnCalc Control’s Click Event Procedure

38

Must call GetFwt function from btnCalc’s Click event procedure

Math.Round functionRound value to specific number of decimal

placesSyntax: Math.Round (value[, digits])

value: Numeric expression to work ondigits: Integer indicating number of places to

right of decimal point



Adding an Existing Form to a Solution

39

• Add an existing form to Chap07/Harvey Industries Solution– Make sure that added form uses a different form name

from any form name of Harvey Industries Solution in • Visual Studio and disk file system

• The splash screen for Country Charming Inn in Chapter 1 is to be integrated into Chap07/Harvey Industries Solution– The splash screen identifies the application’s author

and copyright year, or shows welcome message

實作練習 : 需下載 Chap07/ Harvey Industries Solution Chap07/Splash Solution Chap02/Playtime Solution



Figure 1-31: Completed splash screen

40



1. Rename the form in Splash Solution2. Project-> 加入現有項目 ->Find Splash Form.vb to add

Open a new form by Timer’s Tick event Add following codes in the Tick event of the timer

tmrExitMe.Hide()

tmrExit.Enabled = False

Dim mForm As New frmMain

mForm.ShowDialog()

Me.Close()

Syntax used to instruct the computer to create an object from a class:

Dim variablename As New classname

The name of the main form in Harvey Industries Solution

Otherwise, the form frmMain will show up many times.

41


Include Image File for the Added Form

VB doesn’t import image files automatically for the added

form.

You can do it by one of the following steps

Make the statement Me.picCountry.Image = …… as a

comment

Click Splash Form’s PictureBox picCountry

Use the task box of the PictureBox to set up its image

file (image file is in the Resources folder of the

Chap07/Splash Solution )

42


Assigning the Startup Form

When an application is started, VB.NET automatically invokes the form set as the Startup object of a project

The setup steps for Startup object are as follows:

1. Right click on the project in the Project Explorer Window to open the Properties Window

2. Click the Application tab in Properties Window

3. Click the Startup object ComboBox to set up the startup form → choose frmSplash

43


ShowDialog() vs. Show() Method

A form object’s ShowDialog() method allows you to display the form object on the screen with focus transfer (dialog-style interaction)

The syntax is: form.ShowDialog()

The form object’s Show() method allows you to display a form object on the screen without focus transfer

The syntax is: form.Show ()

44


Show Another Form by a Button

Download Chap02/Playtime Solution, Chap07/Harvey Industries Solution

How to use a button to open a new form

1. Project-> 加入現有項目 ->Find Playtime Form.vb to add

2. Include Image File for the PictureBox PictureBox1

3. Add following codes in the Click event of a button Show Playtime on the Harvey Industries’ MainForm Me.Hide() ‘Show a form at a time

Dim hForm As New frmPlaytime

hForm.ShowDialog()

Me.Show() frmPlaytime.Show() or .ShowDialog() ‘Show 2 forms

frmPlaytime.Focus() (when using frmPlaytime.Show() )

The name of main form in Playtime Solution

45


Lesson C Summary

46

Use form’s FormClosing event procedure to process code when form is about to be closed

Set Cancel property of FormClosing event procedure’s e parameter to true to prevent form from being closed

Use Math.Round function to round number to specific number of decimal places

chapter seven sub and function procedures programming with microsoft visual basic 2010 5 th edition

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