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VB.Net Introduction

VB.Net Introduction. .NET Framework. .NET Framework class libraries: A large set of classes that forms the basis for objects that can be used programmatically.

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VB.Net Introduction

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  1. VB.Net Introduction

  2. .NET Framework • .NET Framework class libraries: A large set of classes that forms the basis for objects that can be used programmatically. • Programming in the .NET Framework means making use of the classes exposed by the Framework, building your own classes on top of these and manipulating the resulting objects. • Creating Internet applications and Windows applications

  3. VB.NET is Object-Oriented • Everything from the simplest data types provided by VB to the complex forms is a class. • Ex: • Dim iNum as Integer • iNum=10 • Debug.WriteLine (“The number is: “ & iNum.ToString)

  4. Visual Studio .NET 2005 • It supports VB.Net, J#, C#, and C++. • Demo: • Start page: Recent projects • Starting project: • File/New Project/Project types: Windows Application • View: • Solution Explorer/Data Sources • Server Explorer • Property Window • ToolBox • Form design view/Form code view • Tools/Option • Environment • Projects and Solutions • VB defaults • Project/Add New Item • Project properties: Right-click project name and choose Properties • Start Up form • Property window example

  5. Introduction to Visual Basic .Net • Event-driven programming • The interface for a VB program consists of one or more forms, containing one or more controls (screen objects). • Form and control has a number of events that it can respond to. Typical events include clicking a mouse button, type a character on the keyboard, changing a value, etc. • Event procedure

  6. Form • Properties: • Name, FormBorderStyle, Text, BackColor, BackImage, Opacity • Events: • Load, FormClosing, FormClosed • GotFocus, LostFocus • MouseOver, Click, DoubleCLick

  7. Typical VB.Net Controls • TextBox • Label • Button • CheckBox • RadioButton • ListBox • ComboBox • PictureBox

  8. Text Box • Properties: • AutoSize, BorderStyle, CauseValidation, Enabled, Locked, Multiline, PasswordChar, ReadOnly, ScrollBar, TabIndex, Text, Visible, WordWrap, etc. • Properties can be set at the design time or at the run time using code. • To refer to a property: • ControlName.PropertyName • Ex. TextBox1.Text

  9. Typical VB.Net Programming Tasks • Creating the GUI elements that make up the application’s user interface. • Visualize the application. • Make a list of the controls needed. • Setting the properties of the GUI elements • Writing procedures that respond to events and perform other operations.

  10. Demo Num1 Num2 Sum = .Control properties .Event: Click, MouseMove, FormLoad, etc. .Event procedures Sum: textBox3.text=CStr(CDbl(textBox1.text)+CDbl(textBox2.text)) Or (CDbl(textBox1.text)+CDbl(textBox2.text)).toString .Challenge: How to draw a horizontal line? .Demo: Text alignment (TextAlign property)

  11. VB Projects • A VB project consists of several files. Visual Studio .Net automatically creates a project folder to keep all project files in the folder. • Project file • Form file • Modules • Class file • Etc.

  12. Configure VB Project • Project property page • Application • Compile • References • Tools/Options • Environment • Projects and Solutions • VB defaults

  13. Variable Declarations • Option Explicit • Dim variableName as DataType • Variable naming rules: • The first character must be a letter or an underscore character. • Use only letters, digits, and underscore. • Cannot contain spaces or periods. • No VB keywords • Naming conventions: • Descriptive • Consistent lower and upper case characters. • Ex. Camel casing: lowerUpper, employeeName

  14. Control Naming Conventions • The first three letters should be a lowercase prefix that indicates the control’s type. • frm, txt, lbl, btn. • The first letter after the prefix should be uppercase. • txtSalary, lblMessage • The part of the control name after the prefix should describe the control’s purpose in the application.

  15. VB Data Types • Boolean (True/False): 2 bytes • Byte: Holds a whole number from 0 to 255. • Char: single character • Date: date and time, 8 bytes. • Decimal: Real number up to 29 significant digits, 16 bytes • Double: real, 8 bytes • Single: real, 4 bytes • Integer: 4 bytes (int32, uint32) • Long: 8 bytes integer • Short: 2 bytes integer • String • Object: Holds a reference of an object

  16. Variable Declaration Examples • Dim empName as String • Declare multiple variables with one Dim: • Dim empName, dependentName, empSSN as String • Dim X As Integer, Y As Single • Initiatialization • Dim interestRate as Double = 0.0715

  17. Variable Default Value • Variables with a numeric data type: 0 • Boolean variables: False • Date variables: 12:00:00 AM, January 1 of the year 1. • String variables: Nothing

  18. Variable Scope • Block-level scope: declared within a block of code terminated by an end, loop or next statement. • If city = “Rome” then • Dim message as string = “the city is in Italy” • MessageBox.Show(message) • End if • Procedural-level scope: declared in a procedure • Class-level, module-level scope: declared in a class or module but outside any procedure with either Dim or Private keyword. • Project-level scope: a module variable declared with the Public keyword.

  19. Data Conversion • Implicit conversion: When you assign a value of one data type to a variable of another data type, VB attempts to convert the value being assigned to the data type of the variable if the OptionStrict is set to Off. • Explicit conversion: • VB.Net Functions: CStr, Ccur, CDbl, Cint, CLng, CSng, Cdate,Val, etc. • .Net System.Convert • Type class’s methods: • toString

  20. Date Data Type • Variables of the Date data type can hold both a date and a time. The smallest value is midnight (00:00:00) of Jan 1 of the year 1. The largest value is 11:59:59 PM of Dec. 31 of the year 9999. • Date literals: A date literal may contain the date, the time, or both, and must be enclosed in # symbols: • #1/30/2003#, #1/31/2003 2:10:00 PM# • #6:30 PM#, #18:30:00# • Note: ControlPanel/RegionalOptions/Date

  21. Date Literal Example: • Dim startDate as dateTime • startDate = #1/30/2003# • Use the System.Convert.ToDateTime function to convert a string to a date value: • startDate = System.Convert.ToDateTime(“1/30/2003”) • If date string is entered in a text box: • startDate = System.Convert.ToDateTime(txtDate.text) • Or startDate=Cdate(txtDate.text) • Date data type format methods

  22. Some Date Functions • Now: Current date and time • Today: Current date • TimeOfDay • DateDiff • Demo • Days between two dates • Days to Christmas • Date data type properties and methods

  23. Using Online HelpExample:Search Help for DateDiff • MSDN • Visual Basic • Reference • Language reference • Functions: • DateDiff Function

  24. Arithmetic and String Operators • +, -, *, /. \, ^ • String Concatenation: &, + • Compound operator: : X= X+1 or X +=1

  25. IF Statement • IF condition THEN statements [ELSEIF condition-n THEN [elseifstatements] [ELSE [elsestatements]]] End If

  26. Select Case Structure • SELECT CASE testexpression [CASE expressionlist-n [Statements] [CASE ELSE [elsestatements] END SELECT

  27. Select Case Example • SELECT CASE temperature CASE <40 Text1.text=“cold” CASE < 60 Text1.text=“cool” CASE 60 to 80 Text1.text=“warm” CASE ELSE Text1.text=“Hot” End Select

  28. Loop • FOR index – start TO end [STEP step] [statements] [EXIT FOR] NEXT index DO [{WHILE| UNTIL} condition] [statements] [EXIT DO] LOOP

  29. Do While/Do Until Private Sub Command1_Click() Dim counter As Integer counter = 0 Do While counter <= 5 Debug.write(counter) counter = counter + 1 Loop Text1.Text = counter End Sub Private Sub Command2_Click() Dim counter As Integer counter = 0 Do Until counter > 5 Debug.write(counter) counter = counter + 1 Loop Text1.Text = counter End Sub

  30. With … End With Convenient shorthand to execute a series of statements on a single object. Within the block, the reference to the object is implicit and need not be written. With TextBox1 .Height = 250 .Width = 600 .Text = “Hello” End With

  31. Procedures . Sub procedure: Sub SubName(Arguments) … End Sub • To call a sub procedure SUB1 • CALL SUB1(Argument1, Argument2, …)

  32. Function • Private Function tax(salary) As Double • tax = salary * 0.1 • End Function • Or • Private Function tax(salary) • Return salary * 0.1 • End Function

  33. Call by Reference Call by Value • ByRef • The address of the item is passed. Any changes made to the passing variable are made to the variable itself. • ByVal • Default • Only the variable’s value is passed.

  34. ByRef, ByVal example Private Sub Button1_Click() Dim myStr As String myStr = TextBox1.Text Call ChangeTextRef (myStr) TextBox1.Text = myStr End Sub Private Sub ChangeTextRef(ByRef strInput As String) strInput = "New Text" End Sub

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