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Chapter 3 Introduction to Visual Basic Environment

Chapter 3 Introduction to Visual Basic Environment. A Visual Basic Application. Application – another name for a program. Interface – is what appears on the screen when the application is running. Program Code – is instructions that tells an application’s objects how to behave.

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Chapter 3 Introduction to Visual Basic Environment

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  1. Chapter 3Introduction to Visual Basic Environment

  2. A Visual Basic Application • Application – another name for a program. • Interface – is what appears on the screen when the application is running. • Program Code – is instructions that tells an application’s objects how to behave. • Object Oriented Programming - Uses classes, which are program code and data, to create objects. • Objects- can have visual representation such as a dialog box, button, Label etc. • Event-driven program – when a program runs due to an object being selected by the user.

  3. The Visual Basic IDE • IDE – Integrated Development Environment. • Used to create a Visual Basic application • The Visual Basic IDE consists of: • Menu Bar • Tool Bar • Tool Box • Project Window • Project Explorer Window • Properties Window • Form Layout Window

  4. The Visual Basic IDE

  5. Visual Basic Environment • Menu Bar • Tool Bar • Project Window • Project Explorer Window • Properties Window • Form Layout Window

  6. Adding Objects to a Form • Form – is a container object for other objects

  7. Design Time • Objects are added during design time • The time during which the applications interface is being created. • Label object is used to display information. • Command Button object is something a user can click on. • Objects are added by clicking and moving your mouse over to the screen and dragging it across the form.

  8. Object Property Values • Properties – defines its appearance, behavior, position, and other attributes. • Each type of objects have many different types of properties.

  9. Label Properties • Name – identifies an object all names should start with the prefix “lbl”. • Caption – changes the text displayed in the label • Font – used to change font style, and size. • Alignment – Changes the alignment of text in a label’s caption (left & right justify and center)

  10. Command Button Properties • Name – identifies the object. Prefix “cmd”. Cannot be change at runtime. • Caption – Changes the text displayed in the command button. • Example: cmdCancelorDone.Caption = “Done”. Form Properties • Name – identifies an object. Prefix “frm”. Cannot change during runtime. • Caption – changes the text displayed in the title bar. • Example: frmUserApp.Caption = “My Application”

  11. Programming Style • When naming an object, it should start with the appropriate prefix and then be descriptive of the object’s purpose.

  12. Resizing and Moving Objects • Selecting an object is done by simply clicking on it. • Resizing by using the drag handle • Marquee Selection – Selecting the pointer control and create a dash box around several objects at one time.

  13. Saving a Project • File menu and select the “Save Project” command or clicking on disk icon shortcut key. • First saved – both form and project must be given descriptive names. • Save the form using the same name as its Name Property and then save the project using a descriptive name of the application.

  14. Running a Visual Basic Application • F5 – start command • Run Menu and select run • Run icon on the toolbar Run Time • Refers to the time during which application is being executed. • A VB program can be run at any time of its development.

  15. End Command • Run Menu – select “End” command. • Click the End icon on the Tool Bar.

  16. Application • Also refer to as Program • Contains set of instructions that tells the computer how to perform specific task. • Each line of code is referred to as a statement. Event Procedures • Is a block of code that executes in response to an event. • Event (User Event) – is a way in which the user can interact with an object, such as clicking a button. • Specific actions will be taken when the user clicks on the button.

  17. Form Module • Container for program code. • Code Editor – is the area displaying the form module View Code button View Object button

  18. Code Editor Window • Display by double-clicking on the form. • Display by clicking on the View Code Button in the Project Explorer. • Clicking the button beside the view code button returns you back to the form.

  19. Unload Statement • Removes a form from memory and ends the application. • Unload statement requires a form name to be unloaded. • If the form to be unloaded is the current form, then you could use Me • Example: • Unload Me or Unload Form1

  20. Examples of Unload Statement

  21. Adding Event Procedures • Select object name from Object list and then a corresponding event is selected from the Event name.

  22. Private • Indicates that the procedure cannot be accessed outside of the form module. • Sub declares the procedures • End Sub – ends the Sub statement. • Body is between Sub and End Sub statements.

  23. Printing A Project • The interface and program code of an application are printed by selecting the print command from the file menu • CTRL + P Removing a Project from the IDE • File menu – Select the Remove Project command.

  24. Using Assignment to Change Property Values • Assignment – is used to change the value of an object property at run time. • Assignment Statement changes property values using the equal sign (=). • Each Object property can only be assigned a valid property values.

  25. AutoList • Is displayed when typing an object’s name and a dot operator notation mark.

  26. Valid Values of the label object properties • Name – Cannot be change during run time by an assignment statement • Caption – Text in double Quote • lblMessage.Caption = “Adios” • Font – has several Subproperties • Size – 0 – 2048 • Example: lblMessage.Font.Size = 10 • Bold & Italic are True or False • Example: lblMessage.Font.Bold = True • Name – enclosed in double quote • lblMessage.Font.Name = “Arial” • Alignment – 0 – left, 1 – right, 2 – center

  27. The Form_Load Event Procedure • Event procedures can also be written for form events. • The Form_Load event procedure is executed when the form is loaded into memory.(Application is started or run) • Examples Private Sub Form_Load() lblSample.Caption = “This text is centered.” lblSample.Alignment = 2 End Sub

  28. Form_Load • Changing object property values in the Form_Load event procedure is alternative to setting property values in the Properties window. • Initializing the form – Setting object properties through the Form_Load event.

  29. Commenting Code • Comments – are used to explain and clarify program code for a human reader. • No effect on how the application runs. • Single quotation mark (‘) begins a comment • Mark code that is ambiguous or misleading. • Example: lblSample.Alignment = 0 ‘left justify • All programs should state the following: • ‘ Author: Your Name • ‘ Date: Current Date • ‘ Chapter and Exercises

  30. Opening a Project • File menu – Open Project • CTRL + O • Open Project Button on the Tool Bar

  31. Graphics • Makes programs more interesting • Makes it easier to interact with.

  32. Image Control • Located in the Tool Box • Used to create Images

  33. Properties of an Image • Name – Use the img prefix when naming and image. • Picture – is used to display a dialog box for selecting the graphic to display in the image area. • Stretch – True or False – True if it has been resized. False otherwise. • Visible – True or False – To display at run time Visible = True. To hide Visible = False.

  34. Image Object • Displays as a box, when added to a form.

  35. Selecting an Image • Go to Property box and select Picture. Click on box on ellipsis. • Stretch should be set to true so image will fit in the image box. Click event • Is when the user clicks on an image object to perform an action.

  36. Operators and Expressions • Built-in arithmetic operators • “^” - exponential • “*” - multiplication • “/” – division • “\” – Integer division • “Mod” - Modulus • “+” - addition • “-” - subtraction

  37. Expression • Arithmetic operators are used to form expressions. • Expression can be anywhere a numeric value is allowed • Example: lblAnswer.Caption = 3.14 * 10^2 • Expressions are NOT enclosed in quotes.

  38. Order of Precedence • Exponentiation • Multiplication and Division Left to Right • Addition and Subtraction Left to Right • You can change order of precedence by using parentheses.

  39. Programming Style • Always use parentheses when any ambiguity or maybe questions about the expression.

  40. Compiler & Interpreter • Visual Basic also has a compiler that translate the program code into separate executable file. • Executable file can be run on any Computer that uses Windows 95 or later. • Visual Basic acts as an interpreter that reads each line of program code as it is entered. • Visual Basic will highlight any errors immediately. • Interpreter executes the code line-by-line and displays the output in the IDE.

  41. Exiting Visual Basic • ALT + Q • File menu – Exit

  42. Visual Basic Programming Guidelines • Create the program interface first • Name all objects before writing and code. • Use Object list in Code Editor window to select the object event procedure.

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