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Visual Basic: Forms, Controls and Events

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... MultiLine AcceptsTab AcceptsReturn WordWrap ScrollBars Events TextChanged CheckState property Checked Unchecked Indeterminate ... Errors (Errors in ... Types of ... – PowerPoint PPT presentation

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Title: Visual Basic: Forms, Controls and Events


1
Visual Basic Forms, Controls and Events
  • CIS 115 Lecture 3

2
Topics
  • Forms
  • Form properties
  • Controls
  • Control properties
  • Event Driven Programming
  • Form Events
  • Control Events
  • Event Handlers
  • VB Example Program

3
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

4
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

5
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

6
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

7
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)

8
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

9
Setting Properties
  • Design Time ? Set in Properties Window
  • Run Time ? Set / Change in Code

10
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

11
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

12
Buttons
  • Properties
  • Text
  • Cancel -gt Cancel
  • -gt
  • Events
  • Click

13
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

14
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

15
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
16
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

17
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

18
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

19
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

20
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

21
Focus and Validation Event Sequence
  • Focus is when an object becomes the Active
    Control
  • Focus Event Sequence
  • Enter
  • GotFocus
  • Leave
  • Validating
  • Validated
  • LostFocus

22
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
23
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
24
Event Driven Programming Components
  • Input
  • Controls
  • Process
  • Events
  • Output
  • Controls

25
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

26
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
27
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

28
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
29
VB Example Textbox Text Changed Event Procedure
(cont.)
  • Add code to the event procedure stub
  • txtFirst.ForeColor Color.Blue

30
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

31
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

32
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

33
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.

34
VB Example Run the Program Again
  • Test All Events
  • Click Quit Button

35
Homework
  • Homework 1
  • Visual Basic Controls and Properties
  • See handout for details and due date
  • Questions?
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