Visual Basic Control Events

2.  Forms
 Form properties
 Controls
 Control properties
 Event Driven Programming
 Form Events
 Control Events
 Event Handlers
 VB Example Program

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

4.  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.  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
 Fixed 3D: 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.  Visual objects that are placed on a form to enable
customized activities
 FamiliarVisual 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 inWindows Form class library,
and are defined
 withToolBox and Form Designer
 or strictly with code

7.  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

8.  DesignTime  Set in
PropertiesWindow
 RunTime  Set / Change in
Code

9. Slide 2- 9
 Specify the control name (btnExit)
 Then a dot
 Then the PropertyName (Visible)
 controlName.propertyName
 btnExit.Visible
▪ refers to theVisible property of the btnExit control
▪ The visible property values may only be true or false

10.  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 theVisible property of the btnExit control
▪ Causes the text of the btnExit control to become hidden to the user
 txtFirstName.text = “Paul”
 txtLastName.text = “Overstreet”

11.  Properties
 Text
▪ &Cancel -> Cancel
▪ && -> &
 Events
 Click

12.  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

13.  Text box allows user to
enter or edit data
 Properties
 MaxLength, MultiLine
 AcceptsTab
 AcceptsReturn
 WordWrap
 ScrollBars
 Events
 TextChanged

14.  CheckState property
 Checked
 Unchecked
 Indeterminate (checked
but grayed)
 Text property displays
built-in caption
If chkMarried.CheckState = CheckState.Checked Then
M
End If

15.  ComboBox Properties
 Text
 DropDownStyle
▪ Simple
▪ Dropdown
▪ DropdownList
 Sorted
 Methods
 Items.Clear
 Items.Add
 Items.Remove
cboChoice.Items.Clear()
cboChoice.Items.Add("First")
cboChoice.Items.Add("Second")
cboChoice.Items.Add("Third")
cboChoice.Items.Add(TextBox1.Text)
cboChoice.Items.Remove("Third")

16.  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 ComponentTray
at design time

17.  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
▪ EnteringText
▪ 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

18.  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

19.  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

20.  Focus is when an object becomes the “Active
Control”
 Focus Event Sequence:
 Enter
 GotFocus
 Leave
 Validating
 Validated
 LostFocus

21.  Create Event Procedure
 Double Click on Control
 Displays CodeWindow and Event Procedure Stub for
default event
Or
 Open the Code Editor (F7 orView Menu:Code Command)
 Select Control & Event from drop down windows in Code
Editor
Event Code Goes In Here

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

23.  Input
 Controls
 Process
 Events
 Output
 Controls

24. UDIE – Implement the solution inVB:
 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

25.  UsingVisual Basic.Net
create the following form
Object Property Setting
Form1 Text Demonstration
txtFirst Text (blank)
txtSecond Text (blank)
btnRed Text Change Color
to Red

26. 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

27. When the text is edited in txtFirst - Change txtFirst text color to blue
 In CodeWindow
 Select the Control for the Event Procedure
 txtFirst from the ClassName box
 Select the Event from the Method Name Box
 TextChanged

28.  Add code to the event procedure stub:
 txtFirst.ForeColor = Color.Blue

29. When txtFirst is deselected - Change txtFirst text color to black
 In CodeWindow
 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

30.  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

31.  Add a Button to your Form
 Name: btnExit
 Text Property: &Quit
 Add a Button Click Event for this Button
 Code: END

32.  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.