VB Net Introduction Visual Studio 2010 Demo Start
VB. Net Introduction
Visual Studio 2010 Demo • Start page: New project/ Open project/Recent projects • Starting project: • File/New Project/ – C# or VB – Windows or Web – Project name • File/New website • Project windows: – Form design view/Form code view – Solution Explorer – Server Explorer – Property Window • Properties and Events – Tool. Box – Project/Add New Item – Project properties: Right-click project name and choose Properties • Start Up form – Property window example
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 controls have events that can respond to. Typical events include clicking a mouse button, type a character on the keyboard, changing a value, etc. – Event procedure
Form • Properties: – Name, Form. Border. Style, Text, Back. Color, Back. Image, Opacity • Events: – Load, Form. Closing, Form. Closed – Got. Focus, Lost. Focus – Mouse. Hover, Click, Double. CLick
Typical VB. Net Controls • • Text. Box Label Button Check. Box Radio. Button List. Box Combo. Box Picture. Box
Text Box • Properties: – Auto. Size, Border. Style, Cause. Validation, Enabled, Locked, Multiline, Password. Char, Read. Only, Scroll. Bar, Tab. Index, Text, Visible, Word. Wrap, etc. • Properties can be set at the design time or at the run time using code. • To refer to a property: – Control. Name. Property. Name – Ex. Text. Box 1. Text – Note: The Text property is a string data type and automatically inherits the properties and methods of the string data type.
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.
To Add an Event-Procedure • 1. Select the Properties window • 2. Click Events button • 3. Select the event and double-click it. • Note: Every control has a default event. • Form: Load event • Button control: Click event • Textbox: Text Changed event – To add the default event procedure, simply double -click the control.
Demo Num 1 Num 2 Sum =. Control properties. Event: Click, Mouse. Move, Form Load, etc. . Event procedures Sum: text. Box 3. text=CStr(CDbl(text. Box 1. text)+CDbl(text. Box 2. text)) Or (CDbl(text. Box 1. text)+CDbl(text. Box 2. text)). to. String. Demo: Text alignment (Text. Align property)
Using VB Functions or. Net Methods? • VB functions: Cstr, Cdbl, … • . Net framework: – System. Convert • Text. Box 3. Text = (System. Convert. To. Double(Text. Box 1. Text) + System. Convert. To. Double(Text. Box 2. Text)). To. String
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.
Configure VB Project • Project property page – Application – Compile – References • Tools/Options – Environment – Projects and Solutions » VB defaults
VB Defaults • Option Explicit: – On --- must declare variables before use • Option Strict: – Off --- VB will convert the data • Option Compare: – Binary --- case sensitive – Text --- case insensitive • Option Infer – On --- When you set Option Infer to On, you can declare variables without explicitly stating a data type. The compiler infers the data type of a variable from the type of its initialization expression.
Variable Declarations • Option Explicit • Dim variable. Name as Data. Type • 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: lower. Upper, employee. Name
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. – txt. Salary, lbl. Message • The part of the control name after the prefix should describe the control’s purpose in the application.
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 (int 32, uint 32) Long: 8 bytes integer Short: 2 bytes integer String Object: Holds a reference of an object
Variable Declaration Examples • Dim emp. Name as String • Declare multiple variables with one Dim: – Dim emp. Name, dependent. Name, emp. SSN as String • Dim X As Integer, Y As Single • Initiatialization – Dim interest. Rate as Double = 0. 0715
Variable Default Value • Variables with a numeric data type: 0 • Boolean variables: False • Date variables: 12: 00 AM, January 1 of the year 1. • String variables: Nothing
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” • Message. Box. 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.
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 Option. Strict 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: – to. String
Date Data Type • Variables of the Date data type can hold both a date and a time. The smallest value is midnight (00: 00) of Jan 1 of the year 1. The largest value is 11: 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: Control. Panel/Regional. Options/Date
• Date Literal Example: – Dim start. Date as date. Time – start. Date = #1/30/2003# • Use the System. Convert. To. Date. Time function to convert a string to a date value: – start. Date = System. Convert. To. Date. Time(“ 1/30/2003”) – If date string is entered in a text box: • start. Date = System. Convert. To. Date. Time(txt. Date. text) • Or start. Date=Cdate(txt. Date. text) • Date data type format methods
Some Date Functions • • • Now: Current date and time Today: Current date Time. Of. Day Date. Diff: Demo – Days between two dates – Days to Christmas • Date. Diff(Date. Interval. Day, Today(), #12/25/2007#) – Date data type properties and methods
Using Online Help • MSDN VB Developer Center – http: //msdn. microsoft. com/enus/vbasic/default. aspx – Learn/Visual Basic language
Arithmetic and String Operators • +, -, *, /. , ^ • String Concatenation: &, + • Compound operator: : X= X+1 or X +=1
IF Statement • IF condition THEN statements [ELSEIF condition-n THEN [elseifstatements] [ELSE [elsestatements]]] End If
Select Case Structure • SELECT CASE testexpression [CASE expressionlist-n [Statements] [CASE ELSE [elsestatements] END SELECT
Select Case Example • SELECT CASE temperature CASE <40 Text 1. text=“cold” CASE < 60 Text 1. text=“cool” CASE 60 to 80 Text 1. text=“warm” CASE ELSE Text 1. text=“Hot” End Select
Loop • FOR index – start TO end [STEP step] [statements] [EXIT FOR] NEXT index DO [{WHILE| UNTIL} condition] [statements] [EXIT DO] LOOP
Do While/Do Until Private Sub Command 1_Click() Dim counter As Integer counter = 0 Do While counter <= 5 Debug. write(counter) counter = counter + 1 Loop Text 1. Text = counter End Sub Private Sub Command 2_Click() Dim counter As Integer counter = 0 Do Until counter > 5 Debug. write(counter) counter = counter + 1 Loop Text 1. Text = counter End Sub
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 Text. Box 1. Height = 250. Width = 600. Text = “Hello” End With
Procedures . Sub procedure: Sub. Name(Arguments) … End Sub – To call a sub procedure SUB 1 • CALL SUB 1(Argument 1, Argument 2, …)
Function • Private Function tax(salary) As Double • tax = salary * 0. 1 • End Function – Or • Private Function tax(salary) • Return salary * 0. 1 • End Function
Call by Reference Call by Value • By. Ref – The address of the item is passed. Any changes made to the passing variable are made to the variable itself. • By. Val – Default – Only the variable’s value is passed.
By. Ref, By. Val example Private Sub Button 1_Click(By. Val sender As System. Object, By. Val e As System. Event. Args) Handles Button 1. Click Dim my. Str As String my. Str = Text. Box 1. Text Call Change. Text. Ref (my. Str) Text. Box 1. Text = my. Str End Sub Private Sub Change. Text. Ref(By. Ref str. Input As String) str. Input = "New Text" End Sub
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