Visual Basic: Introduc1on Object Oriented Programming in VB.NET
Visual Basic: Introduc1on
Object Oriented Programming in VB.NET
Visual Studio.NET
¡ A pla@orm that allows the development and deployment of desktop and web applica1ons
¡ Allows user choice of many .NET languages § May program in One of them § May create different parts of applica1on in different languages ▪ Visual Basic ▪ C# (C Sharp) ▪ C++ ▪ J++ ▪ Etc.
Visual Studio.NET
¡ Integrated Development Environment – allows the automa1on of many of the common programming tasks in one environment § Wri1ng the code § Checking for Syntax (Language) errors § Compiling and Interpre1ng(Transferring to computer language)
§ Debugging (Fixing Run-‐1me or Logic Errors) § Running the Applica1on
What is Visual Basic.Net
¡ 4th Genera1on Programming Environment / Development Language
¡ Based on BASIC language § Beginners All-‐Purpose Symbolic Instruc1onal Code
¡ Most widely used tool for developing Windows Applica1ons § Graphical User Interface (GUI) § Menus, Bu\ons, Icons to help the user
¡ Full Object-‐Oriented Programming Language
How a VB Applica1on is Compiled and Run
Solution
.NET FrameworkVisual Studio .NET
Project
CommonLanguageRuntime
IntegratedDevelopmentEnvironment
Source files
Visual Basiccompiler
1 2 3
Assembly
Intermediate Language (IL)
Class references
Project and Solu1on Concepts
• User creates a new project in Visual Studio – A solu1on and a folder are created at the same 1me with the same name as
the project – The project belongs to the solu1on – Mul1ple projects can be included in a solu1on
• Solu1on – Contains several folders that define an applica1on’s structure – Solu1on files have a file suffix of .sln
• Project: contains files for a part of the solu1on – Project file is used to create an executable applica1on – A project file has a suffix of .vbproj – Every project has a type (Console, Windows, etc.) – Every project has an entry point: A Sub procedure named Main or a Form
Project and Solu1on Folders/Files • Solu1on folder
– Solu1on file (.sln) – Project folder
• Project file (.vbproj) • Visual Basic source files (.vb) • My Project folder: contains configura1on informa1on common to all projects
– The file AssemblyInfo.vb contains assembly metadata – The References folder contains references to other assemblies
• The bin folder contains the executable file produced as a result of compiling the applica1on
Using Visual Studio.NET
Crea1ng an Applica1on • Select the “Create Project” op1on from the “Recent
Projects” box on the Start Page
Default Se`ngs
Visual Basic Forms
• This is a Visual Basic GUI object called a form
• Forms are the windows and dialog boxes that display when a program runs.
• A form is an object that contains other objects such as bu\ons, text boxes, and labels
Visual Basic Controls
• Form elements are objects called controls
• This form has: – Two TextBox controls – Four Label controls – Two Bu1on controls
• The value displayed by a control is held in the text property of the control
• Lea bu\on text property is Calculate Gross Pay • Bu\ons have methods a\ached to events
Design Window T
oolbox
Solu1on Explorer
Proper1es Window
Crea1ng the Applica1on
• Step 1: Add a Control to the Form – Bu\on – Look in the Toolbox for the Bu\on Control – Select the Bu\on with the Mouse – Draw a Rectangle Region in the Design Window by holding the mouse bu\on down
– Release the mouse bu\on to see your bu\on – (Can also be added by double clicking on the bu\on in the Toolbox)
Crea1ng the Applica1on
• Add a Second Bu\on to the Form • Put it in the lower right corner
• The project now contains • a form with 2 bu\on • controls
Control Proper1es
• Proper1es – All controls have proper1es – Each property has a value (or values) – Determine the Look and Feel (and some1mes behavior) of a Control
– Set ini1ally through the Proper1es Window
• Proper1es Set for this Applica1on – Name – Text
Name Property
• The name property establishes a means for the program to refer to that control
• Controls are assigned rela1vely meaningless names when created
• Change these names to something more meaningful
• Control names must start with a le\er • Remaining characters may be le\ers, digits, or underscore
Examples of Names
btnCalcGrossPay btnClose
txtHoursWorked
txtPayRate
lblGrossPay
Label1
Label2
Label3
§ The label controls use the default names (Label1, etc.)
§ Text boxes, buttons, and the Gross Pay label play an active role in the program and have been changed
Control Naming Conven1ons
• Should be meaningful • 1st 3 lowercase le\ers indicate the type of control
– txt… for Text Boxes – lbl… for Labels – btn… for Bu\ons
• Aaer that, capitalize the first le\er of each word • txtHoursWorked is clearer than txthoursworked
• Change the name property – Set the name of bu\on1 to btnWelcome – Set the name of bu\on2 to btnExit
Se`ng Control Proper1es
• Click on the Control in the Design Window • Select the appropriate property in the Proper1es Window
Text Property
• Determines the visible text on the control • Change the text property
– bntWelcome à set to “Say Welcome” – btnExit à set to “Exit”
– Do not need to include the “ “ in your text field – No1ce how the bu\ons now display the new text
Event Driven Programming
• The GUI environment is event-‐driven • An event is an ac1on that takes place within a program – Clicking a bu\on (a Click event) – Keying in a TextBox (a TextChanged event)
• Visual Basic controls are capable of detec1ng many, many events
• A program can respond to an event if the programmer writes an event procedure
Event Procedures • An Event Procedure is a block of code that executes only when par1cular event occurs
• Wri1ng an Event Procedure – Create the event procedure stub
• Double click on control from Design Window – for default event for that control
OR • Open the Code Editor (F7 or View Menu/Code op1on) • Select Control & Select Event from drop down windows in Code Editor
– Add the event code to the event procedure stub
Open the Code Editor
Select the Control for the Event Procedure
• Select the btnWelcome control from the Form Controls List Box
Select the Event for the Event Procedure
• Select the Click event from the list of many available events
• Bu\ons have 57 possible events they can respond to
Event Procedure Stub • Beginning of Procedure is created for you
– If you create stub by double clicking on control it will create a stub for the most commonly used event for that control
Add the Event Code
• Write the code that you want executed when the user clicks on the btnWelcome bu\on – Type: MsgBox (“Welcome to Visual Basic”)
– Must be contained within the Event Procedure Stub
Wri1ng Visual Basic Code • Not Case Sensi1ve
– Visual Basic will “correct” case issues for you • Keywords are in Blue
– Special reserved words • Comments in Green • Problems with Syntax (Language) will be underlined in blue
Coding Conven1ons
• Rules – Use spaces to separate the words and operators – Indenta1on and capitaliza1on have no effect
• Recommenda1ons – Use indenta1on and extra spaces for alignment – Use blank lines before and aaer groups of related statements
– Code all variable declara1ons at the start of the procedure
– Group related declara1ons
Comments • Usage
– Type an apostrophe ( ' ) followed by the comment – The compiler ignores everything on the line aaer ‘ – Used for documenta1on/readability and to disable chosen statements during tes1ng
• Recommenda1ons – Follow apostrophe with a star for readability ( ‘* ) – Use at beginning of program to indicate author, purpose, date, etc.
– Use for groups of related statements and por1ons of code that are difficult to understand
Code that follows recomenda1ons '* ====================================== '* Class: CIS 115-‐101 '* Author: Paul Overstreet '* Purpose: Homework 1 – VB ApplicaDon '* Date: 11/30/01 '* ======================================
Public Class Form1
Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventAr…
'*Variable declaraDons Dim dOrderTotal As Decimal Dim dDiscountAmount As Decimal
'*Get total from textbox dOrderTotal = txtOrderTotal.Text
'*Calculate the proper discount dDiscountAmount = dOrderTotal * 0.25 ' dDiscountAmount = dOrderTotal * 0.25
End Sub
Private Sub BuYon1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)…
‘*Code goes here
End Sub
End Class
Create Event Procedure for Exit Bu\on
• Create an Event Procedure for when the btnExit bu\on is clicked
• Have it display “Goodbye” in a MsgBox • Then “End” – this will terminate the program
Switching to Design Window
• You can switch between the Design Window and the Code Window (once opened) by clicking on the tabs at the top of the
• Design and Code Windows – Form1.vb(Design) is the – design window – Form1.vb is the Code Window
Running the Applica1on
¡ Click the Run Icon on the Standard Toolbar
¡ Or Press F5
¡ This will begin the program ¡ Display the Form/Window ¡ Nothing will happen § Wai1ng on an Event
Test the Events
• Click on the “Say Welcome” bu\on – The message box should display
• Click on the “Exit” bu\on – The message box should display – The applica1on should terminate
Save the Project
• Make sure to save your work – SAVE ALL (not Save Form) – Visual Basic applica1ons are – made of several files -‐ – Oaen even several forms