Visual Basic: Forms, Controls and Events

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Visual Basic Forms, Controls and Events

• CIS 115 Lecture 3

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Topics

• Forms
• Form properties
• Controls
• Control properties
• Event Driven Programming
• Form Events
• Control Events
• Event Handlers
• VB Example Program

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Forms

• A form is a container for controls
• A form is used to design a GUI-based window in a
  Windows application
• A form displays information and receives input
  from the user.
• Always orient a form at a task as defined by the
  user

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Form Properties

• Text defines the text to display in the caption
  bar
• StartPosition determines position of form when
  it first appears (eg. CenterScreen)
• Size.Width, Size.Height the 2D area occupied by
  the form, in units of pixels
• Location.X, Location.Y the relative position of
  the form on the screen
• Visible can be seen by the user
• Enabled the user can interact with the form

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Form Properties (cont.)

• FormBorderStyle determines the appearance and
  behavior of the borders of the form
• Sizable (Default) Has min, max, and close
  buttons can be resized by dragging edges
• Fixed3D Has a 3D look min, max, and close
  buttons cannot be resized
• FixedSingle Has single line border min, max,
  and close buttons cannot be resized
• AcceptButton - designates which button on the
  form is activated by the Enter Key
• Cancel Button - designates which button on the
  form is activated by the ESC Key

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Controls

• Visual objects that are placed on a form to
  enable customized activities
• Familiar Visual Basic controls
• Label - displays text the user cannot change
• TextBox - allows the user to enter text
• Button performs an action when clicked
• RadioButton - A round button that is selected or
  deselected with a mouse
• CheckBox A box that is checked or unchecked
  with a mouse click
• Form - A window that contains these controls
• Built-in controls defined in Windows Form class
  library, and are defined
• with ToolBox and Form Designer
• or strictly with code

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Types of Controls w/Prefixes

• Text edit (TextBoxtxt___)
• Text display (Labeldefault name or lbl___)
• Selection from a list (ListBoxlst___,
  ComboBoxcbo___, ListView, TreeView,
  NumericUpDown)
• Graphic display (PictureBoxpic___)
• Graphic storage (ImageList)
• Value setting (CheckBoxchk___, CheckListBox,
  RadioButton,)
• Date setting (DateTimePicker, MonthCalendar)
• Dialog boxes (OpenFileDialog, PrintDialog)
• Menu controls (MainMenu, )
• Commands (Buttonbtn___, LinkLabel)
• Grouping other controls (GroupBox, TabControl,
  Panel)

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Control Properties - Common

• Common properties shared by many controls
• Name, Text
• Size.Height Width, Location.X Y, Dock
• BackColor Sets the background (fill) color
• ForeColor Sets the foreground (text) color
• CanFocus, ContainsFocus, Focused
• Visible Enabled determine availability to user
• Font properties affect text display in the
  control
• Font, size, bold, etc.
• Tab Index Tab Stop

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Setting Properties

• Design Time ? Set in Properties Window
• Run Time ? Set / Change in Code

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Syntax for Referring to theValue of a Control's
Property

• Specify the control name (btnExit)
• Then a dot
• Then the PropertyName (Visible)
• controlName.propertyName
• btnExit.Visible
• refers to the Visible property of the btnExit
  control
• The visible property values may only be true or
  false

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Assignment Statement Set/ Change the Value of a
Control Property

• Item to receive the value (Left Side)
• Assignment Indicator
• Value to be assigned(Right Side)
• VariableName Value
• NumberVariable 5
• ControlName.PropertyName Setting
• btnExit.Visible False
• Assigns the value False to the Visible property
  of the btnExit control
• Causes the text of the btnExit control to become
  hidden to the user
• txtFirstName.text Paul
• txtLastName.text Overstreet

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Buttons

• Properties
• Text
• Cancel -gt Cancel
• -gt
• Events
• Click

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Labels and LinkLabels

• Use labels and link labels for text display
• Text property (no more Caption) defines text to
  display
• User cannot change a label
• LinkLabel enables hyperlinks
• Links.Add inserts a hyperlink into text
• Must write event-handler to invoke browser
• See example

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Text Boxes Text Input, Edit, and Display

• Text box allows user to enter or edit data
• Properties
• MaxLength, MultiLine
• AcceptsTab
• AcceptsReturn
• WordWrap
• ScrollBars
• Events
• TextChanged

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CheckBox Control

• CheckState property
• Checked
• Unchecked
• Indeterminate (checked but grayed)
• Text property displays built-in caption

If chkMarried.CheckState CheckState.Checked
Then M End If
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List Selection Controls

• cboChoice.Items.Clear()
• cboChoice.Items.Add("First")
• cboChoice.Items.Add("Second")
• cboChoice.Items.Add("Third")
• cboChoice.Items.Add(TextBox1.Text)

• ComboBox Properties
• Text
• DropDownStyle
• Simple
• Dropdown
• DropdownList
• Sorted
• Methods
• Items.Clear
• Items.Add
• Items.Remove

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Timer Control

• Executes code after a specified interval
• Timer Event
• Unique event that executes after the interval
  specified in the interval property expires
• Interval Property
• 0 - 65,535 milliseconds
• 0 - means disabled
• 60,000 milliseconds is one minute
• Enabled property must also be true for timer to
  work.
• Timer control is never visible at run time
• Stored in Component Tray at design time

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Event Driven Programming

• Applications recognize and respond to events by
  executing code known as event procedures
• Event An action that is recognized by an
  object.
• User Actions
• Mouse Click
• Entering Text
• Pressing a Key
• Program Calculations
• Triggered by the system
• Timer
• Event Handler Code that is written by the
  programmer to respond to an event
• Executes only when particular event occurs

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Form Events

• Common Form Events
• Form1_Load() - Occurs before a form is displayed
  for the first time.
• Form1_Activated() - Occurs when form becomes the
  active window - through code or by user
• Form1_Deactivate() - Occurs when the form loses
  focus and is not the active form
• Form1_Closing() - Occurs when the form closes,
  either through an event or the windows close
  button being clicked

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Control Events

• Many controls share a Common set of events to
  which they can react
• Click, DoubleClick
• MouseMove, MouseDown, MouseUp, MouseWheel,
  MouseHover, MouseLeave
• KeyPress, KeyDown, KeyUp
• Resize
• DragDrop
• GotFocus
• LostFocus

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Focus and Validation Event Sequence

• Focus is when an object becomes the Active
  Control
• Focus Event Sequence
• Enter
• GotFocus
• Leave
• Validating
• Validated
• LostFocus

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Coding Event Handlers

• Create Event Procedure
• Double Click on Control
• Displays Code Window and Event Procedure Stub for
  default event
• Or
• Open the Code Editor (F7 or View MenuCode
  Command)
• Select Control Event from drop down windows in
  Code Editor

Event Code Goes In Here
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Event Handler Example

• Exit Button Clicked Method (btnExit_Click)

Marks the beginning of this event procedure
Name of the control that owns the event procedure
Name of the event the procedure responds to
Line Continuation Mark
Private Sub btnExit_Click(ByVal sender As
System.Object, _ ByVal e As System.EventArgs)
Handles btnExit.Click ' End the
application End End Sub
Event handled by this procedure
Ends the program
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Event Driven Programming Components

• Input
• Controls
• Process
• Events
• Output
• Controls

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Event Driven Programming Implementation Phase
Steps

• UDIE Implement the solution in VB
• Create the Interface
• Input Controls
• Output Controls
• Set the Properties
• Configure the appearance and behavior of the
  controls
• Write the Code to execute when events occur
• Process the inputs to create the outputs

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VB Example The Interface

• Using Visual Basic.Net create the following form

Object Property Setting
Form1 Text Demonstration
txtFirst Text (blank)
txtSecond Text (blank)
btnRed Text Change Color to Red
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VB Example Button Click Event Procedure

• When btnRed is clicked - Change txtFirst text
  color to red
• Double Click on btnRed
• Code window should appear
• (with Event Procedure Stub)
• Add code to the event procedure stub
• txtFirst.ForeColor Color.Red

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VB Example Textbox Text Changed Event Procedure

• When the text is edited in txtFirst - Change
  txtFirst text color to blue
• In Code Window
• Select the Control for the Event Procedure
• txtFirst from the ClassName box
• Select the Event from the Method Name Box
• TextChanged

Method Name Box
Class Name Box
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VB Example Textbox Text Changed Event Procedure
(cont.)

• Add code to the event procedure stub
• txtFirst.ForeColor Color.Blue

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VB Example Textbox Leave Event Procedure

• When txtFirst is deselected - Change txtFirst
  text color to black
• In Code Window
• Select the Control for the Event Procedure
• txtFirst from the ClassName box
• Select the Event from the Method Name Box
• Leave
• Add code to the event procedure stub
• txtFirst.ForeColor Color.Black

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VB Example Run the Program

• Click F5 or the Run Button
• Type Hello into the 1st textbox
• What Happens
• Click on the 2nd Textbox
• What happened in txtFirst and Why
• Click on the Button
• What happened in txtFirst
• Type Friends into the 1st textbox
• Stop Program by clicking Red X in corner

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VB Example Exit Button Clicked Event Procedure

• Add a Button to your Form
• Name btnExit
• Text Property Quit
• Add a Button Click Event for this Button
• Code END

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VB Example Code Editor

• Finds Syntax Errors (Errors in Programming
  Language)
• Return to btnRed Click Event Procedure
• Add this line of Code
• txtSecond.text Hello
• Notice Wavy Blue Line This indicates a Syntax
  Error that must be fixed.

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VB Example Run the Program Again

• Test All Events
• Click Quit Button

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Homework

• Homework 1
• Visual Basic Controls and Properties
• See handout for details and due date
• Questions?