outline

Properties

• Properties are a number of variables associated with an object
• Each object has a different list of properties
• Some properties are common to most objects (visible)
• Some properties are specific to only one type of object (Max, Min in scroll bars)

Properties Characteristics

• Can have different types of values:
  - Text (caption)
  - Numeric (min, max)
  - Boolean - True/False (visible)

Properties are used to:

• Refine an object's appearance (BackColor)
• Refine an object's behavior (Enabled)
• Set up the object so it will do what the programmer wants (Design time)
• Change the characteristics of the property while the program is running (Run time)

Properties can be changed at:

• Design time:
  - as the program is being built
  - uses the properties box
  - All properties will be set this way when the program starts execution

Properties can be changed at:

• Run time:
  - while the program is running
  - is accomplished using code
  - allows properties to be changed on the fly
  - allows response to environmental (user) input

Example:

• MyFirst used
  - design time to set up the BackColor of the picture boxes
  - run time to set up the BackColor of the form

Methods

• A special kind of command attached to specific objects
• Works only with the object it is attached to
• Some objects (check boxes) have a few methods
• Others (data controls) have many

Method Characteristics

• Usually found searching the online help
• Activated only in run time
• Relatively limited use
• Syntax: Object.Method

Examples

• Move event - used to move an object
• Syntax - Object.Move X, Y, Height, Width
  - where X and Y are coordinates the object will be moved to
  - height and width are the size of the object

Common Methods

• Hide, Show used with forms
• AddItem used with listboxes, grids
• Print, EndDoc to print to printer

Events

• Are the stimuli an object can recognize
• Are listed in the Proc box of the object's code window
• Some events are nearly universal (e.g., Click)
• Can be activated by the user (e.g., Click)
• Some are object specific (e.g., Timer)

Event Driven Program Design

• Most code in Visual Basic is related to an object-event relationship
• The user or environment activates events in objects, which then activates code
• Very different than earlier types of program organization techniques

Example:

• Picture1_Click in last week's program
• Read 'When the user CLICKS on the PICTURE1 control, this will happen.'

Common Events

• Click, Double-click
• Load, Unload on forms
• Change on controls that get user input
• Paint on controls that contain graphical information

Getting Help

• Visual Basic is a complex, growing language with many subtleties
• Traditional reference books are cumbersome
• There is a hypertext online help which uses a Windows help engine

Help Menu in VB

• Contents and submenu is good if you need general information
• Search for Help on - is much more flexible
  - type in whatever you want help on
  - a list of similar topics will appear
  - select the topic you want

Keyword Help

• This is the fastest way to get help
• Type or point to a keyword that you are having trouble with in a code window
• Be sure the cursor is somewhere inside that word
• Hit the F1 key
  - if the word is a keyword and spelled correctly,
  a help screen for that word will appear
  - good for checking syntax

General Declarations

• This is an area that can be used to make comments about your program
• Example:
  'Create a clock that displays a time in a label.
  'Place two horizontal scroll bars on the form,
  'one that will change the backcolor of the clock label and one
  'that will change the forecolor of the clock label.

Some New Objects

• Timer
  - is invisible at run time
  - goes 'off' at specified intervals
  - used to replace loops

Timer Properties

• Interval (in 1000ths of a second)
• Enabled (True or False)

Timer Events

• Timer
  - it has 'gone off'

New Properties

• BackColor, ForeColor - attached to most objects
• FontName - tells which font to use in current object
• FontSize - tells the size of the current font

New Functions

• QBColor
  - gets a color using the Qbasic value
  - uses a number between 0 and 15
  - is an easy way to get most common colors

Sample Syntax

• frmSample.BackColor = QBColor (4)

Time

• Time (displays 12 hour clock)
• Time$ (displays 24 hour clock)
• Gets the current time from the system clock and returns it as a string

Sample Syntax:

• lblTime.Caption = Time
  or
  lblTime.Caption = Time$

End

• Ends the program

Syntax Examples

• Private Sub Timer1_Timer()
     'when the form loads the clock
     'should appear in the lblClockFace
     'caption area
     lblClockFace.Caption = Time
  End Sub