Introduction to Visual Basic (VB)

Topics 1. What is VB? 2. What is Event-Driven? 3. What is Object-Orientation? 4. Objects used in VB 5. VB objects naming practice 6. Files in VB 7. OOED Programming process 8. VB statements 9. VB Help

What is VB? A windows-based system using objects responding to events An objected-oriented event-driven programming language

Event-Driven Procedural languages – run from start to finish with no human intervention Basic, COBOL, FORTRAN, C Event driven languages - waits for an event to occur before taking any action Example of event The press of a key on the keyboard Movement of the mouse The click of a mouse button Programming in Windows is usually termed event-driven programming

Objects Reusable software components that model items in the real world e.g. GPA calculator, Tax calculator They are self-contained modules that combine data and program code which pass strictly defined messages to one another

Encapsulation The capability of an object to hide its internal workings from other objects. In VB, programmers does not need to know what is going on inside the object, but only need to know how to work with the object’s properties and methods How many drivers are mechanics?

Object-Oriented Event-Driven Programming (OOED) OOED uses objects in the program and runs only after the Events occur OOED is easier to work with Users can combine multiple objects to create new systems or extend existing ones

Starting VB from your computer … Toolbox [p. 27] Project Window [p. 28] useful icons Properties windows [p. 30] How to Add Controls [p. 36] How to Add Code [p. 39] The toolbar icons [p. 43]

1st Project (ShowName) A Form Three Command Buttons One Text Box Click Me Exit One Text Box One Label

Forms and Controls as Objects Forms and Controls are two kinds of objects you may use in VB A form is a virtual blank space to design the user interface for a VB application The tools that you use to construct the user interface are controls E.g. command button and textbox etc.

VB objects naming practice: Start the name with a standard object abbreviation cmd = command button, txt = text box, frm = form. Finish the name with a descriptive word of the objects purpose Spaces and special characters are not allowed in an objects name. (E.g. cmdCancel) Examples might be: frmMain.BackColor = vbRed txtState.Text = ""

Features of Objects The programmer can manipulate the object through the use of three key object features: properties methods events

Object Properties A property is a named attribute of an object. Using an analogy to English grammar, if an object is thought of as a noun, then a property may be thought of as an adjective. Used to change the appearance of objects. An example of the relationship between objects and properties using an everyday object: shirt.color = "Green“ shirt.launder = "Clean“ We use dot (“.”) notation

Setting Values of Properties During design time, properties may be set in the Properties Window. You are in “Design Time” when you are designing the project and adding code Some properties may be set or modified during run time. You are in “Run Time” when you click the VCR Run icon

Object Methods A set of predefined activities that an object can carry out. The syntax for using an objects method is: object.method A method is a verb that can be carried out by the object. For the various VB objects, there are usually several methods already available. Or advanced programmers can create their own methods.

Methods Example Real life example A Visual Basic example dog.eat dog.bark dog.run A Visual Basic example E.g. frmMain.hide

Object Event VB example An action taken by the object when notified by a message Or, user actions taken on the object that provokes a response from the object. Examples Soccer ball: kicking, throwing, holding etc. Cat: feeding, hitting, calling etc. mouse click, form load, or key press. VB example Private Sub cmdsubmit_Click() … End Sub

Files in Visual Basic All projects in VB have a .vbp (project) file and at least one .frm (form file) file. Always save .frm files first and then save project files. Use File|Save or File|Save as… commands for this purpose or click Disk icon on toolbar. Projects with graphics also have .frx (binary form) files. They are saved automatically. Module files have a .bas extension and are pure code files.

Save files Save early. All three types can and should have same names. Important! Save early. All three types can and should have same names. Eliminate prefix (eg.frm)

Add graphic Retrieve your 1st project from your disk Use image control Select a graphic Change the size of graphic Stretch property of image control Save the project

Save it Use your last name Eg. chen.frm, chen.vbp, chen.frx Create a folder in your disk composed of your name Copy files to your folder Drag the folder to: W:\apps\classes\mist4600\homework\ Dchen\testfile folder

OOED Programming Process A six step process for writing an OOED computer program: 1. Define problem. 2. Create interface 3. Develop logic for action objects 4. Write and test code for action objects 5. Test overall project 6. Document project in writing

More Practice (step 1 to 3 only) Circle problem revisit I: radius P: calculate circumference, calculate area O: radius, circumference, area Payroll problem revisit I: employee name, pay rate, and hours worked P: calculate gross pay O: gross pay

Comments To explain the purpose of a program, or a statement, a comment statement is added For yourself and others Any statement beginning with an apostrophe or REM is a comment Comments can be added to end of statements using apostrophe

VB Statements A statement is a reserved word Statements are instructions that are built into the Visual Basic language Some examples are: End Option Explicit Private Sub Dim

Visual Basic Help There are three types of Help: Help menu option context-sensitive help and Auto Help In VB 6, Help uses the familiar Internet Explorer browser interface for the first two types of help. You can seek help by selecting Contents, Index, or Search from the Help menu item

Context-Sensitive and Auto Help With context-sensitive help, pressing the F1 key provides help on whatever item the cursor is located. With Auto Help, VB tries to help you with a code statement by providing: A list of items to complete the statement Info on the statement you have started Tips on the type of data you are working with