Lecture 9
Additional Topics in VB.NET
1
Timer Control
• Invisible during runtime
• Triggers an event after a specified period of time
• The Interval property specifies the time period –
measured in milliseconds
• To begin timing, set the Enabled property to True
• To stop timing, set the Enabled property to False
• The event triggered each time is called Tick event
2
Timer Control (cont.)
• Interval property
• Between 0 and 65,535 milliseconds
• 1,000 milliseconds = 1 second
• Enabled property
• False (default) ==> Do not run Tick event
• True ==> Run Tick event at designated
interval
• Tick event
• Runs each time the Timer's designated
interval elapses, if Enabled = True
3
DateTimePicker & Calendar Controls
• DateTimePicker
• Takes less screen space
• Displays only day and date unless user
drops down the calendar
• MonthCalendar
• Displays calendar
• Provide the ability to display calendars on
your form
4
Calendar Controls (cont.)
DateTimePicker
MonthCalendar
5
Getting Input from an
Input Dialog Box
stringVar = InputBox(prompt, title)
fileName = InputBox("Enter the name " _
& "of the file containing the " & _
"information.", "Name of File")
6
Using a Message Dialog Box
for Output
• Displays a message in a dialog box,
waits for the user to click a button
MsgBox(prompt)
MsgBox("Nice try, but no cigar")
7
Some Built-In Functions
Function
Example
Input
Output
Int
Int(2.6) is 2
number
number
Chr
Chr(65) is “A”
number
string
Asc
Asc(“Apple”) is 65
string
number
Math.Round
Math.Round(2.7) is
3
number
number
Math.Sqrt
Math.Sqrt(9) is 3
Number
number
8
Built-in Functions (2)
• Functions return a value
IsNumeric(9) ' Returns True
IsNumeric(459.95) ' Returns True
IsNumeric(“45 help”) ' Returns False
9
Input Validation
• Code If structure to determine if value
falls within a range of acceptable values
• Refer to lab 6 – Calculate Grade
• Use single If for each value, Else for message to
user, and execute Focus Method to reset focus to
text box
10
Input Validation (2)
• Check to see if valid values were entered
by user in TextBox and use Message Box
to notify user if invalid
• IsNumeric function checks for numeric
values
• If IsNumeric(txtQuantity.Text) Then ...
• Check for required data or not blank
• If txtName.Text <> "" Then ...
11
Variables
• Declaration:
Dim speed As Double
Variable name
Data type
• Assignment:
speed = 50
12
Initial Value of a Integer
• An integer is a whole number
• Declaring an integer variable:
Dim varName As Integer
(Numeric variables are automatically initialized to 0)
• To specify a nonzero initial value
Dim varName As Double = 50
13
Initial Value of a String
• By default the initial value is Nothing
• Strings can be given a different initial
value as follows:
Dim today As String = "Monday"
14
Incrementing
• To add 1 to the numeric variable var
var = var + 1
• Or as a shortcut
var +=1
15
Multiple Declarations
Dim a As Integer
Dim b As Integer
Alternative method: Multiple-declaration
Dim a, b As Integer
16
Remark Statement
• Also known as Comment, used for
documentation
• Non-executable
• Automatically colored Green in Editor
• Begins with an apostrophe ( ' )
• On a separate line from executable code
• At the right end of a line of executable
code
' Display the Hello World message
17
Assignment Statement
• Assigns a value to a property or variable
• Operates from right to left
• Enclose text strings in quotation marks (" ")
lblMessage.Text=" Hello World "
18