Introducing Visual Basic

Transcription

1 Introducing Visual Basic September 8, 2006 Chapter 3 - VB 2005 by Schneider 1

2 Today Chapter 3 provides a great walkthrough intro to VB We re going to take a detailed look at this today (and pick it up next week) We ll keep the pace even, but feel free to offer feedback to the prof we can always adjust as necessary depending on the needs of the class! Chapter 3 - VB 2005 by Schneider 2

3 Next week Kim s going to be back She ll keep going with today s material (and a quick recap) Be prepared for your first assignment later next week Also, Kim will get the website up this weekend! She promises ;) Chapter 3 - VB 2005 by Schneider 3

4 Chapter 3 Fundamentals of Programming in Visual Basic 3.1 Visual Basic Controls 3.2 Visual Basic Events 3.3 Numbers 3.4 Strings 3.5 Input and Output Chapter 3 - VB 2005 by Schneider 4

5 3.1 Visual Basic Controls Invoking Visual Basic Text Box Control Button Control Label Control List Box Control Name Property Fonts / Auto Hide Positioning and Aligning Controls Chapter 3 - VB 2005 by Schneider 5

6 Visual Basic Start Page Chapter 3 - VB 2005 by Schneider 6

7 Start a New Project Chapter 3 - VB 2005 by Schneider 7

8 New Project Dialog Box Chapter 3 - VB 2005 by Schneider 8

9 Initial Visual Basic Screen Chapter 3 - VB 2005 by Schneider 9

10 Toolbox Chapter 3 - VB 2005 by Schneider 10

11 3 Ways to Place a Control from the Toolbox onto the Form Window Double-click Drag Click, Point, and Drag Chapter 3 - VB 2005 by Schneider 11

12 Four Controls at Design Time Text box To select a control, click on it. Sizing handles will appear when a control is selected. Chapter 3 - VB 2005 by Schneider 12

13 Text Box Control Used for input and output When used for output, ReadOnly property is set to True Tasks button Sizing handles Chapter 3 - VB 2005 by Schneider 13

14 Properties Window Press F4 to display the Properties window for the selected control. Categorized view Alphabetical view Chapter 3 - VB 2005 by Schneider 14

15 Properties Window Selected control Properties Settings Chapter 3 - VB 2005 by Schneider 15

16 Some Often Used Properties Text Autosize Font.Name Font.Size ForeColor BackColor ReadOnly Chapter 3 - VB 2005 by Schneider 16

17 Setting Properties Click on property name in left column. Enter its setting into right column by typing or selecting from options displayed via a button or ellipses ( ). Chapter 3 - VB 2005 by Schneider 17

18 Setting the ForeColor Property 1. Click on ForeColor. 2. Click on button at right of settings box. 3. Click on Custom tab to obtain display shown. 4. Click on a colour. Chapter 3 - VB 2005 by Schneider 18

19 Font Property 1. Click on Font in left column. 2. Click on ellipsis at right of settings box to obtain display shown, 3. Make selections. Chapter 3 - VB 2005 by Schneider 19

20 Button Control The caption on the button should indicate the effect of clicking on the button. Text property determines caption. Chapter 3 - VB 2005 by Schneider 20

21 Add an "access key" Chapter 3 - VB 2005 by Schneider 21

22 Label Control Used to identify the contents of a text box. Text property specifies caption. By default, label automatically resizes to accommodate caption on one line. When the AutoSize property is set to False, label can be resized manually. Used primarily to obtain a multi-rowed label. Chapter 3 - VB 2005 by Schneider 22

23 List Box Control Initially used to display several pieces of output. Later used to select from a list. Chapter 3 - VB 2005 by Schneider 23

24 The Name Property How the programmer refers to a control in code Setting for Name property near top of Properties window. Name must begin with a letter, be less than 215 characters long, and may include numbers and letters. Use appropriate 3- or 4-character naming prefix Chapter 3 - VB 2005 by Schneider 24

25 Control Name Prefixes Control button label text box list box Prefix btn lbl txt lst Example btncompute lbladdress txtaddress lstoutput Chapter 3 - VB 2005 by Schneider 25

26 Renaming the Form Initial name is Form1 The Solution Explorer window lists a file named Form1.vb. To rename the form, change the name of this file to newname.vb newname should begin with prefix frm. Chapter 3 - VB 2005 by Schneider 26

27 Fonts Proportional width fonts take up less space for "I" than for "W" like Microsoft Sans Serif Fixed-width fonts take up the same amount of space for each character like Courier New Fixed-width fonts are good for tables. Chapter 3 - VB 2005 by Schneider 27

28 Auto Hide Hides Toolbox when not in use Vertical push pin icon indicates auto hide is disabled. Click the push pin to make it horizontal and enable auto hide. Push pin Chapter 3 - VB 2005 by Schneider 28

29 Positioning Controls Proximity line Chapter 3 - VB 2005 by Schneider 29

30 Aligning Controls Snap line Chapter 3 - VB 2005 by Schneider 30

31 Aligning Controls Snap line Chapter 3 - VB 2005 by Schneider 31

32 3.2 Visual Basic Events An Event Procedure Walkthrough Properties and Event Procedures of the Form The Header of an Event Procedure Chapter 3 - VB 2005 by Schneider 32

33 Event An event is an action, such as the user clicking on a button Usually, nothing happens in a Visual Basic program until the user does something and generates an event. What happens is determined by statements. Chapter 3 - VB 2005 by Schneider 33

34 Sample Statements txtbox.forecolor = Color.Red txtbox.visible = True txtbox.text = Hello World General Form: controlname.property = setting Chapter 3 - VB 2005 by Schneider 34

35 Sample Form txtfirst txtsecond btnred Chapter 3 - VB 2005 by Schneider 35

36 Focus When you click on a text box, a cursor appears in the text box, and you can type into the text box. Such a text box is said to have the focus. If you click on another text box, the first text box loses the focus and the second text box receives the focus. Chapter 3 - VB 2005 by Schneider 36

37 Examples of Events btnshow.click txtbox.textchanged txtbox.leave General Form: controlname.event Chapter 3 - VB 2005 by Schneider 37

38 The three steps in creating a Visual Basic program: 1. Create the interface; that is, generate, position, and size the objects. 2. Set properties; that is, configure the appearance of the objects. 3. Write the code that executes when events occur. Chapter 3 - VB 2005 by Schneider 38

39 Code Window Page tab Class Name box Method Name box Chapter 3 - VB 2005 by Schneider 39

40 Structure of an Event Procedure Header Private Sub objectname_event(...) Handles objectname.event statements End Sub (...) is filled automatically with (ByVal sender As System.Object, ByVal e As System.EventArgs) Chapter 3 - VB 2005 by Schneider 40

41 Code Window Page tab Class Name box Method Name box Chapter 3 - VB 2005 by Schneider 41

42 Create an Outline for an Event Procedure; i.e. header and End Sub 1. Double-click on a control or 2. Use the Class Name and Method Name boxes. (We primarily use the first method.) Chapter 3 - VB 2005 by Schneider 42

43 Sample Form txtfirst txtsecond btnred Double Click on txtfirst Chapter 3 - VB 2005 by Schneider 43

44 Code for Walkthrough Public Class frmdemo Private Sub txtfirst_textchanged(...) Handles txtfirst.textchanged End Sub End Class Chapter 3 - VB 2005 by Schneider 44

45 Code for Walkthrough Public Class frmdemo Private Sub txtfirst_textchanged(...) Handles txtfirst.textchanged txtfirst.forecolor = Color.Blue End Sub End Class Chapter 3 - VB 2005 by Schneider 45

46 IntelliSense Automatically pops up to give the programmer help. Chapter 3 - VB 2005 by Schneider 46

47 Code Window Click tab to return to Form Designer Chapter 3 - VB 2005 by Schneider 47

48 Sample Form txtfirst txtsecond btnred Double-click on btnred Chapter 3 - VB 2005 by Schneider 48

49 Code for Walkthrough Public Class frmdemo Private Sub txtfirst_textchanged(...) Handles txtfirst.textchanged txtfirst.forecolor = Color.Blue End Sub Private Sub btnred_click(...) Handles btnred.click End Sub End Class Chapter 3 - VB 2005 by Schneider 49

50 Code for Walkthrough Public Class frmdemo Private Sub txtfirst_textchanged(...) Handles txtfirst.textchanged txtfirst.forecolor = Color.Blue End Sub Private Sub btnred_click(...) Handles btnred.click txtfirst.forecolor = Color.Red End Sub End Class Chapter 3 - VB 2005 by Schneider 50

51 Event Procedure txtfirst.leave Select txtfirst from Class Name box drop-down list. Select Leave from Method Name box drop-down list. Chapter 3 - VB 2005 by Schneider 51

52 Code for Walkthrough Private Sub txtfirst_leave(...) Handles txtfirst.leave End Sub Private Sub txtfirst_textchanged(...) Handles txtfirst.textchanged txtfirst.forecolor = Color.Blue End Sub Private Sub btnred_click(...) Handles btnred.click txtfirst.forecolor = Color.Red End Sub Chapter 3 - VB 2005 by Schneider 52

53 Code for Walkthrough Private Sub txtfirst_leave(...) Handles txtfirst.leave txtfirst.forecolor = Color.Black End Sub Private Sub txtfirst_textchanged(...) Handles txtfirst.textchanged txtfirst.forecolor = Color.Blue End Sub Private Sub btnred_click(...) Handles btnred.click txtfirst.forecolor = Color.Red End Sub Chapter 3 - VB 2005 by Schneider 53

54 Header of Event Procedure Private Sub btnred_click( ) Handles btnred.click Name, can be changed. Identifies event Private Sub Button_Press( ) Handles btnred.click Chapter 3 - VB 2005 by Schneider 54

55 Handling Multiple Events Event procedure can be invoked by two events. Private Sub Button_Click(...) Handles btnred.click, txtsecond.leave txtfirst.forecolor = Color.Red End Sub Chapter 3 - VB 2005 by Schneider 55

56 Altering Properties of the Form The following won't work: frmdemo.text = "Demonstration" The form is referred to by the keyword Me. Me.Text = "Demonstration" Chapter 3 - VB 2005 by Schneider 56

57 3.3 Numbers Arithmetic Operations Variables Incrementing the Value of a Variable Built-In Functions: Math.Sqrt Int Math.Round Chapter 3 - VB 2005 by Schneider 57

58 Numbers continued The Integer Data Type Multiple Declarations Parentheses Three Types of Errors Chapter 3 - VB 2005 by Schneider 58

59 Arithmetic Operations Numbers are called numeric literals Five arithmetic operations in Visual Basic + addition - subtraction * multiplication / division ^ exponentiation Chapter 3 - VB 2005 by Schneider 59

60 Numeric Expressions * (4 + 5) 2 ^ 3 Chapter 3 - VB 2005 by Schneider 60

61 Displaying Numbers Let n be a number or a numeric expression. The statement lstbox.items.add(n) displays the value of n in the list box. Chapter 3 - VB 2005 by Schneider 61

62 Example 1: Form Chapter 3 - VB 2005 by Schneider 62

63 Example 1: Code and Output Private Sub btncompute_click (...) Handles btncompute.click lstresults.items.add(5) lstresults.items.add(2 * 3) lstresults.items.add((2 ^ 3) 1) End Sub Output 5 in list 6 box 7 Chapter 3 - VB 2005 by Schneider 63

64 Example 1: Code using With Private Sub btncompute_click (...) Handles btncompute.click With lstresults.items.add(5).add(2 * 3).Add((2 ^ 3) 1) End With End Sub Chapter 3 - VB 2005 by Schneider 64

65 Numeric Variable A numeric variable is a name to which a number can be assigned. Examples: speed distance interestrate balance Chapter 3 - VB 2005 by Schneider 65

66 Variables Declaration: Dim speed As Double Variable name Data type Assignment: speed = 50 Chapter 3 - VB 2005 by Schneider 66

67 Initialization Numeric variables are automatically initialized to 0: Dim varname As Double To specify a nonzero initial value Dim varname As Double = 50 Chapter 3 - VB 2005 by Schneider 67

68 Numeric Expressions Numeric variables can be used in numeric expressions. Dim balance As Double = 1000 lstbox.items.add(1.05 * balance) Output: 1050 Chapter 3 - VB 2005 by Schneider 68

69 Assignment Statement Dim numvar1 As Double = 5 Dim numvar2 As Double = 4 numvar1 = 3 * numvar2 lstbox.items.add(numvar1) Output: 12 Chapter 3 - VB 2005 by Schneider 69

70 Incrementing To add 1 to the numeric variable var var = var + 1 Or as a shortcut var += 1 Or as a generalization var += numeric expression Chapter 3 - VB 2005 by Schneider 70

71 Built-in Functions Functions return a value Math.Sqrt(9) returns 3 Int(9.7) returns 9 Math.Round(2.7) is 3 Chapter 3 - VB 2005 by Schneider 71

72 Integer Data Type Variables of type Double can be assigned both whole numbers and numbers with decimals. The statement Dim varname As Integer declares a numeric variable that can only be assigned whole number values between about -2 billion and 2 billion. Chapter 3 - VB 2005 by Schneider 72

73 Multiple Declarations Dim a, b As Double Two other types of multiple-declaration statements are Dim a As Double, b As Integer Dim c As Double = 2, b As Integer = 5 Chapter 3 - VB 2005 by Schneider 73

74 Parentheses Parentheses should be used liberally in numeric expressions. In the absence of parentheses, the operations are carried out in the following order: ^, * and /, + and -. Chapter 3 - VB 2005 by Schneider 74

75 Three Types of Errors Syntax error Run-time error Logic error Chapter 3 - VB 2005 by Schneider 75

76 Some Types of Syntax Errors Misspellings lstbox.itms.add(3) Omissions lstbox.items.add(2 + ) Incorrect punctuation Dim m; n As Integer Chapter 3 - VB 2005 by Schneider 76

77 A Type of Run-time Error Overflow error Dim numvar As Integer = numvar = numvar * numvar Chapter 3 - VB 2005 by Schneider 77

78 A Logical Error Dim average As Double Dim m As Double = 5 Dim n As Double = 10 average = m + n / 2 Value of average will be 10. Should be 7.5. Chapter 3 - VB 2005 by Schneider 78

79 3.4 Strings Variables and Strings Using Text Boxes for Input and Output Concatenation String Properties and Methods: Length Trim IndexOf ToUpper ToLower Substring Chapter 3 - VB 2005 by Schneider 79

80 Strings continued The Empty String Initial Value of a String Option Strict Internal Documentation Line-Continuation Character Chapter 3 - VB 2005 by Schneider 80

81 String Literal A string literal is a sequence of characters surrounded by quotation marks. Examples: "hello" " " "#ab cde?" Chapter 3 - VB 2005 by Schneider 81

82 String Variable A string variable is a name to which a string value can be assigned. Examples: country ssn word firstname Chapter 3 - VB 2005 by Schneider 82

83 String Variable Declaration: Dim firstname As String Variable name Data type Assignment: firstname = "Fred" Chapter 3 - VB 2005 by Schneider 83

84 String Variable You can declare a string variable and assign it a value at the same time. Dim firstname As String = "Fred" Chapter 3 - VB 2005 by Schneider 84

85 Add Method Let str be a string literal or variable. Then, lstbox.items.add(str) displays the value of str in the list box. Chapter 3 - VB 2005 by Schneider 85

86 String Variable You can assign the value of one string variable to another. Dim strvar1 As String = "Hello" Dim strvar2 As String = "Goodbye" strvar2 = strvar1 lstoutput.items.add(strvar2) Output: Hello Chapter 3 - VB 2005 by Schneider 86

87 Variables and Strings Private Sub btndisplay_click(...) Handles btndisplay.click Dim today As String today = "Monday" lstoutput.items.add("hello") lstoutput.items.add(today) End Sub Output: hello Monday Chapter 3 - VB 2005 by Schneider 87

88 Using Text Boxes for Input and Output The contents of a text box is always a string Input example strvar = txtbox.text Output example txtbox.text = strvar Chapter 3 - VB 2005 by Schneider 88

89 Data Conversion Because the contents of a text box is always a string, sometimes you must convert the input or output. dblvar = CDbl(txtBox.Text) Converts a String to a Double txtbox.text = CStr(numVar) Converts a number to a string Chapter 3 - VB 2005 by Schneider 89

90 Concatenation Combining two strings to make a new string quote1 = "We'll always " quote2 = "have Paris." quote = quote1 & quote2 txtoutput.text = quote & " - Humphrey Bogart" Displays We'll always have Paris. - Humphrey Bogart Chapter 3 - VB 2005 by Schneider 90

91 Appending To append str to the string variable var var = var & str Or as a shortcut var &= str Chapter 3 - VB 2005 by Schneider 91

92 Appending Example Dim var As String = "Good" var &= "bye" txtbox.text = var OUTPUT: Goodbye Chapter 3 - VB 2005 by Schneider 92

93 String Properties and Methods "Visual".Length is 6. "Visual".ToUpper is VISUAL. "123 Hike".Length is 8. "123 Hike".ToLower is 123 hike. "a" & " bcd ".Trim & "efg" is abcdefg. Chapter 3 - VB 2005 by Schneider 93

94 Positions in a String Positions of characters in a string are numbered 0, 1, 2,. Consider the string Visual Basic. Position 0: V Position 1: i Position 7: B Substring al begins at position 4 Chapter 3 - VB 2005 by Schneider 94

95 Substring Method Let str be a string. str.substring(m, n) is the substring of length n, beginning at position m in str. Visual Basic.Substring(2, 3) is sua Visual Basic.Substring(0, 1) is V Chapter 3 - VB 2005 by Schneider 95

96 IndexOf Method Let str1 and str2 be strings. str1.indexof(str2) is the position of the first occurrence of str2 in str1. (Note: Has value -1 if str2 is not a substring of str1.) "Visual Basic".IndexOf("is") is 1. "Visual Basic".IndexOf("si") is 9. "Visual Basic".IndexOf("ab") is -1. Chapter 3 - VB 2005 by Schneider 96

97 The Empty String The string "", which contains no characters, is called the empty string or the zero-length string. The statement lstbox.items.add("") skips a line in the list box. The contents of a text box can be cleared with either the statement txtbox.clear() or the statement txtbox.text = "" Chapter 3 - VB 2005 by Schneider 97

98 Initial Value of a String By default the initial value is Nothing Strings can be given a different initial value as follows: Dim today As String = "Monday" Chapter 3 - VB 2005 by Schneider 98

99 Option Strict Visual Basic allows numeric variables to be assigned strings and vice versa, a poor programming practice. To turn this feature off, put the following statement at the very top of the code window Option Strict On Chapter 3 - VB 2005 by Schneider 99

100 Option Strict On for All Programs Select Options from the Tools menu In left pane, expand Projects and Solution Select VB Defaults Set Option Strict to On Chapter 3 - VB 2005 by Schneider 100

101 With Option Strict On Dim dblvar As Double, intvar As Integer Dim strvar As String Not Valid: Replace with: intvar = dblvar intvar = CInt(dblVar) dblvar = strvar dblvar = CDbl(strVar) strvar = intvar strvar = CStr(intVar) Chapter 3 - VB 2005 by Schneider 101

102 Comments Private Sub btncompute_click (...) Handles btncompute.click 'Calculate the balance in an account Dim rate As Double 'Annual rate of interest Dim curbalance As Double 'Current balance Chapter 3 - VB 2005 by Schneider 102

103 Internal Documentation 1. Other people can easily understand the program. 2. You can understand the program when you read it later. 3. Long programs are easier to read because the purposes of individual pieces can be determined at a glance. Chapter 3 - VB 2005 by Schneider 103

104 Automatic Colorization Comments green String literals maroon Keywords blue Note: Keywords are words such as Sub, Handles, Private, With, and End that have special meaning in Visual Basic. They cannot be used as variable names. Chapter 3 - VB 2005 by Schneider 104

105 Line-Continuation Character A long line of code can be continued on another line by using an underscore (_) preceded by a space msg = "I'm going to make " & _ "him an offer he can't refuse." Chapter 3 - VB 2005 by Schneider 105

106 3.5 Input and Output Formatting Output with Format Functions Formatting Output with Zones Reading Data from Files Getting Input from an Input Dialog Box Using a Message Dialog Box for Output Using a Masked Text Box for Input Chapter 3 - VB 2005 by Schneider 106

107 Formatting Output with Format Functions Function FormatNumber( , 1) FormatCurrency( , 2) FormatPercent(0.183, 0) String Value 12,345.6 $12, % Chapter 3 - VB 2005 by Schneider 107

108 Formatting Output with Zones Use a fixed-width font such as Courier New Divide the characters into zones with a format string. Dim fmtstr As String = "{0, 15}{1, 10}{2, 8}" lstoutput.items.add(string.format(fmtstr, _ data0, data1, data2)) Chapter 3 - VB 2005 by Schneider 108

109 Formatting Output with Zones Dim fmtstr As String = "{0, -15}{1, 10}{2, 8}" lstoutput.items.add(string.format(fmtstr, _ data0, data1, data2)) Here, 15 was preceded by a minus sign. This produces left justification in 0 th zone. There will be right justification in the other two zones. Chapter 3 - VB 2005 by Schneider 109

110 Zone Formatting Symbols Symbols: N, C, and P :Nr :Cr :Pr Effect on zone FormatNumber(data, r) FormatCurrency(data, r) FormatPercent(data, r) Dim fmtstr As String = "{0,15:N1}{1,10:C2}{2,8:P0}" Chapter 3 - VB 2005 by Schneider 110

111 Reading Data from Files Data can be stored in files and accessed with a StreamReader object. We assume that the files are text files (that is, have extension.txt) and have one piece of data per line. Chapter 3 - VB 2005 by Schneider 111

112 Sample File: PAYROLL.TXT Mike Jones John Smith Name Hourly wage Number of hours worked Chapter 3 - VB 2005 by Schneider 112

113 Steps to Use StreamReader Execute a statement of the form Dim readervar As IO.StreamReader = _ IO.File.OpenText(filespec) or the pair of statements Dim readervar As IO.StreamReader readervar = IO.File.OpenText(filespec) Chapter 3 - VB 2005 by Schneider 113

114 Steps to Use StreamReader Read items of data in order, one at a time, from the file with the ReadLine method. strvar = readervar.readline After the desired items have been read from the file, terminate the communications link readervar.close() Chapter 3 - VB 2005 by Schneider 114

115 Example using StreamReader Dim name As String Dim wage, hours As Double Dim sr As IO.StreamReader = _ IO.File.OpenText("PAYROLL.TXT") name = sr.readline wage = CDbl(sr.ReadLine) hours = CDbl(sr.ReadLine) lstbox.items.add(name & ": " & wage * hours) OUTPUT: Mike Jones: Chapter 3 - VB 2005 by Schneider 115

116 Comment on Example Consider lstbox.items.add(name & ": " & wage * hours) The ampersand automatically converted wage * hours into a string before concatenating. We didn t have to convert wage * hours with CStr. Chapter 3 - VB 2005 by Schneider 116

117 Getting Input from an Input Dialog Box stringvar = InputBox(prompt, title) filename = InputBox("Enter the name " _ & "of the file containing the " & _ "information.", "Name of File") Title Prompt Chapter 3 - VB 2005 by Schneider 117

118 Using a Message Dialog Box for Output MsgBox(prompt, 0, title) MsgBox("Nice try, but no cigar.", 0, _ "Consolation") Title Prompt Chapter 3 - VB 2005 by Schneider 118

119 Masked Text Box Similar to an ordinary text box, but has a Mask property that restricts what can be typed into the masked text box. Chapter 3 - VB 2005 by Schneider 119

120 Input Mask Dialog Box Chapter 3 - VB 2005 by Schneider 120

121 Mask A Mask setting is a sequence of characters, with 0, L, and & having special meanings. 0 Placeholder for a digit. L Placeholder for a letter. & Placeholder for a character or space. Chapter 3 - VB 2005 by Schneider 121

122 Sample Masks State abbreviation: LL Phone number: Social Security Number: License plate: &&&&&& Chapter 3 - VB 2005 by Schneider 122