chapter 31 fundamentals of programming in visual basic (vb) visual basic events simple statement
DESCRIPTION
Chapter 33 Assignment Statements Assign a value to a property. General Form: source = value A value on the right- hand side of = is assigned to the left- hand size of =.TRANSCRIPT
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Chapter 3 1
Fundamentals of Programming in Visual Basic (VB)• Visual Basic Events• Simple Statement
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Chapter 3 2
Event• An event is an action, such as the user
clicking on a button• Usually, nothing happens in a Visual Basic
program until the user does something and generates an event.
• What happens is determined by statements. Visual Basic Events
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Chapter 3 3
Assignment Statements• Assign a value to a property.
General Form:
source = value
• A value on the right-hand side of = is assigned to the left-hand size of =.
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Chapter 3 4
Sample Statements • txtBox.ForeColor = Color.Red• txtBox.Visible = True• txtBox.Text = “Hello World”
General Form:
controlName.property = setting
Value represented by setting is stored into controlName.property
Color is a structure allowing us to specify various colors
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Chapter 3 5
Lab• Refers to the examples in the Lab
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Chapter 3 6
Sample Form
txtFirsttxtSecondbtnRed
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Chapter 3 7
Focus
• When you click on a text box, a cursor appears in the text box, and you can type into the text box.
• Such a text box is said to have the focus.• If you click on another text box, the first text
box loses the focus and the second text box receives the focus.
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Chapter 3 8
Examples of Events • btnShow.Click• txtBox.TextChanged• txtBox.Leave
General Form:
controlName.event
This event occurs when a mouse is clicked on the button btnShow
This event occurs when user changes the text of txtBoxThis event occurs
when the input focus leaves txtBox
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Chapter 3 9
The three steps in creating a Visual Basic program:1. Create the interface; that is, generate,
position, and size the objects.2. Set properties; that is, configure the
appearance of the objects.3. Write the code that executes when
events occur.
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Chapter 3 10
Code Window
Method Name box
Class Name box
Page tab
Page tab: 1. frmDemo.vb is a code window2. frmDemo.vb [design] is a design window (to manipulate the window appearance)
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Chapter 3 11
Structure of an Event Procedure
Private Sub objectName_event(...) Handles objectName.event statements End Sub
Header
(...) is filled automatically with (ByVal sender As System.Object, ByVal e As System.EventArgs)
To specify which event will trigger this procedure.
The name of the procedure
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Chapter 3 12
Code Window
Method Name box
Class Name box
Page tab
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Chapter 3 13
Create an Outline for an Event Procedure; i.e. header and End Sub
1. Double-click on a control or2. Use the Class Name and Method Name boxes.
(We primarily use the first method.)
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Chapter 3 14
Sample Form
txtFirst
txtSecond
btnRed
Double Click on txtFirst
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Chapter 3 15
Code for Walkthrough
Public Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged
End SubEnd Class
TextChanged event occurs when the user changes the text of a TextBox
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Chapter 3 16
Code for Walkthrough
Public Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End SubEnd Class
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Chapter 3 17
IntelliSense
Automatically pops up to give the programmer help.
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Chapter 3 18
Code Window
Click tab to return to Form Designer
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Chapter 3 19
Sample Form
txtFirst
txtSecond
btnRed
Double-click on btnRed
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Chapter 3 20
Code for Walkthrough
Public Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub
Private Sub btnRed_Click(...) Handles btnRed.Click
End SubEnd Class
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Chapter 3 21
Code for Walkthrough
Public Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub
Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.Red End SubEnd Class
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Chapter 3 22
Event Procedure txtFirst.Leave• Select txtFirst from Class Name box
drop-down list.• Select Leave from Method Name box
drop-down list.
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Chapter 3 23
Code for WalkthroughPrivate Sub txtFirst_Leave(...) Handles txtFirst.Leave End Sub
Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.BlueEnd Sub
Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.RedEnd Sub
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Chapter 3 24
Code for WalkthroughPrivate Sub txtFirst_Leave(...) Handles txtFirst.Leave txtFirst.ForeColor = Color.BlackEnd Sub
Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.BlueEnd Sub
Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.RedEnd Sub
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Chapter 3 25
Header of Event ProcedurePrivate Sub btnRed_Click(…) Handles btnRed.Click
Identifies the event that
triggers the procedure
Name, can be changed.
Private Sub Button_Press(…) Handles btnRed.Click
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Chapter 3 26
Handling Multiple Events
Private Sub Button_Click(...) Handles btnRed.Click, txtSecond.Leave txtFirst.ForeColor = Color.RedEnd Sub
Event procedure can be invoked by two events.
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Chapter 3 27
Altering Properties of the Form
• The following won't work: frmDemo.Text = "Demonstration"
• The form is referred to by the keyword Me. Me.Text = "Demonstration“