Microsoft Visual Basic 2005
CHAPTER 5
Mobile Applications
Using Decision Structures
5
Objectives
►Write programs for devices other than a personal
computer
►Understand the use of handheld technology ( aka
smart devices )
►Write handheld applications for a Personal Digital
Assistant
►Use the Panel object
►Place RadioButton objects in applications
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Objectives
►Display a message box
►Make decisions using If…Then statements
►Make decisions using If…Then…Else statements
►Make decisions using nested If statements
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5
Objectives
►Make decisions using logical operators
►Make decisions using Case statements
►Insert code snippets
►Test input to ensure a value is numeric
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Chapter Project
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Pervasive Devices
►Visual Studio has a built-in emulator that
displays a “working” Pocket PC
►Pervasive devices have become important in
many business venues
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Create a Smart Device Application
►New Project
►if necessary, click the plus sign next to Smart Device
in the Project types pane on the left side of the New
Project dialog box
►Click Pocket PC 2003 under Smart Device in the
Project types list.
►In the Templates pane, click Device Application
►Change the Name of the Smart Device application
from DeviceApplication1 to WoodCabinetEstimate.
Click the OK button
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Create a Smart Device Application
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Placing Objects on the PocketPC Form Object
►Many of the same objects used in a Windows
application can be placed on the PocketPC Form
object
►You cannot resize the Form object
►The PocketPC Form object can be named in the
same manner as a Windows Form object using the
(Name) property in the Properties window
►Change the Text property of the PocketPC Form
object from Form1 to Estimate in the same manner
used for the Windows Form object
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Placing Objects on the PocketPC Form Object
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Using the Panel Object
► If necessary, open the Device Containers category of the
Toolbox by clicking the plus sign next to the category
name.
► A Panel is used as a container for other controls. In this
application it will be used to group radio buttons.
► (Name) property --- > pnlWoodType
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Using the Panel Object
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Adding the 3 RadioButton Objects
►Drag and drop one RadioButton object from the
Toolbox onto the PocketPC Form object inside
the Panel object.
►Drag a second RadioButton object from the
Toolbox onto the PocketPC Form object using
blue snap lines to align and separate the
RadioButton objects vertically
►add a third RadioButton object
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Adding the RadioButton Objects
► Name the RadioButton objects (Name) property
► The names for the radio buttons, from top to bottom,
should be:
• radPine
• radOak
• radCherry
► Change the Text property for each RadioButton
• Pine
• Oak
• Cherry
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Adding the RadioButton Objects
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Windows Application Container Objects
GroupBox controls
are typically used to group radio buttons, but they are
NOT available for smart devices so for a smart device
use a
Panel control
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GroupBox versus Panel
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Displaying a Message Box
1 – 4 Arguments ( overloaded )
• Message to be displayed
• Caption to display in the title bar
[ blank if omitted ]
• MessageBoxButton to be displayed
[ OK if omitted
• MessageBoxIcon to be displayed
[ blank if omitted ]
]
The Show method returns a value of type DialogResult
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Values Returned by a MessageBox
[ returns a value of type DialogResult ]
DialogResult Enumeration
Specifies identifiers to indicate the return value of a dialog box.
Member name
Abort
Description
The dialog box return value is Abort (usually sent from a button labeled Abort).
Cancel
The dialog box return value is Cancel (usually sent from a button labeled Cancel).
Ignore
The dialog box return value is Ignore (usually sent from a button labeled Ignore).
No
None
OK
Retry
Yes
The dialog box return value is No (usually sent from a button labeled No).
Nothing is returned from the dialog box. This means that the modal dialog continues
running.
The dialog box return value is OK (usually sent from a button labeled OK).
The dialog box return value is Retry (usually sent from a button labeled Retry).
The dialog box return value is Yes (usually sent from a button labeled Yes).
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Displaying a Message Box
[ 1 Argument ]
[ The Show method takes up to 4 arguments ]
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Displaying a Message Box
[ 2 Arguments ]
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Displaying a Message Box
[ 3 Arguments ]
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Displaying a MessageBox
MessageBoxButtons
Specifies constants defining which buttons to display on a MessageBox.
These are defined as an enumeration
Member name
Description
OK
The message box contains an OK button. [ default ]
OKCancel
The message box contains OK and Cancel buttons.
AbortRetryIgnore
YesNoCancel
YesNo
RetryCancel
The message box contains Abort, Retry, and Ignore buttons.
The message box contains Yes, No, and Cancel buttons.
The message box contains Yes and No buttons.
The message box contains Retry and Cancel buttons.
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Displaying a Message Box
[ This is for a MsgBox Function… ]
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Displaying a Message Box
[ 4 Arguments ]
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Displaying a Message Box
[ Enumeration Constants ]
There is also the member name None for which no icon is displayed
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Displaying a Message Box
►In the code editing window, inside the event handler
you are coding, press CTRL+SPACEBAR.
IntelliSense displays the allowable entries. Type mes
to select MessageBox in the IntelliSense list
►Type a period ( . ) to insert the dot operator.
IntelliSense displays a list of the allowable entries.
Type s to select Show in the IntelliSense list
►Type the following text: (“You have been
disconnected from the Internet”, “ISP”)
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Displaying a Message Box
►Here are the last two arguments for the Show
method:
• MessageBoxButtons.RetryCancel
• MessageBoxIcon.Warning
►Type a right parenthesis and then press the
ENTER key
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Displaying a Message Box
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Displaying a Message Box
[ 2 arguments ]
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Making Decisions with Conditional Statements
Using an If…Then Statement
►A decision structure is one of the three
fundamental control structures used in computer
programming.
Sequence, Selection, Repetition
►When a condition is tested in a Visual Basic
program, the condition either is true or false
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If...Then...Else Statement
Conditionally executes a group of statements, depending on the value of an expression.
If condition [ Then ]
[ statements ]
[ ElseIf elseifcondition [ Then ]
[ elseifstatements ] ]
[ Else
[ elsestatements ] ]
End If
-orIf condition Then [ statements ] [ Else elsestatements ]
Anything in brackets ( [ ] ) is optional
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Relational Operators
[ used to create expressions (conditions) ]
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Relational Operators
Characters are compared using their ordinal value in the Unicode
Character Set.
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Comparing Strings
► A string value comparison compares each character in
two strings, starting with the first character in each string
( using ordinal values in the Unicode Character Set )
If the strings are not the same size, the shorter string is padded on
the right with spaces to make it the same length.
Note: spaces come earlier in the collating sequence than do letters
and numbers.
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Comparing Different Data Types
►Every type of data available in Visual Basic can be
compared
• Different numeric types can be compared to each
other [ numerically ]
• A single string character can be compared to a
Char data type [ using ordinal values ]
• If comparing a string to a character literal and
option strict is on, you must use the type character
C.
“a” is a String, “a”C is a Char…
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Using the If…Then…Else Statement
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Using the If…Then…ElseIf Statement
Notice the use of
the type character D
making the Double
literals type Decimal
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Nested If Statements
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Nested If Statements
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Matching If, Else, and End If Entries
► If statements must be fully contained within the outer If
statement
► Place the correct statements with the correct If and Else
statements within the nested If statement
• This illustration shows incorrect logic
( this is a LOGIC error, not a SYNTAX error )
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Testing the Status of a RadioButton Object in Code
Checked is a Boolean variable. You do not need to write:
If Me.radPine.Checked = True then
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Block-Level Scope
► Scope is determined by where the variable is accessible
within a program
► Within an event handler, an If…Then…Else statement is
considered a block of code
► Variables can be declared within a block of code
• The variable can be referenced only within the block of
code where it is declared
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Using Logical Operators
►When more than one condition is included in an
If...Then...Else statement, the conditions are
called a compound condition
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Using the And Logical Operator
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Using the Or Logical Operator
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Using the Not Logical Operator
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Other Logical Operators
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Order of Operations for Logical Operators
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Select Case Statement
►In some programming applications, different
operations can occur based upon the value in a
single field
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Select Case Statement
Select...Case Statement (Visual Basic)
Runs one of several groups of statements, depending on the value of an expression.
Select [ Case ] testexpression
[ Case expressionlist
[ statements ] ]
[ Case Else
[ elsestatements ] ]
End Select
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Select Case Statement
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Select Case Statement
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Select Case Test Expressions
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Using Relational Operators
in a Select Case Statement
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Using Ranges in Select Case Statements
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Selecting Which Decision Structure to Use
►You might be faced with determining if you should
use the Select Case statement or the If...Then...ElseIf
statement to solve a problem
►Generally, the Select Case statement is most useful
when more than two or three values must be tested
for a given variable
►The If...Then...ElseIf statement is more flexible
• More than one variable can be used in the
comparison
• Compound conditions with the And, Or, and Not
logical operators can be used
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Code Snippets
►Right-click the line in the code editing window
where you want to insert the snippet
►Click Insert Snippet on the shortcut menu
►Double-click Common Code Patterns, which is a
folder that contains commonly used code such as
the If...Then...Else statement
►Double-click the Conditionals and Loops folder
because an If...Then...Else statement is a
conditional statement
►Double-click the If...Else...End If Statement code
snippet
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Code Snippets
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Validating Data
►Developers should anticipate that users will enter
invalid data
►Developers must write code that will prevent the
invalid data from being used in the program to
produce invalid output
Visual Basic Language Reference
IsNumeric Function (Visual Basic)
Returns a Boolean value indicating whether an expression can be evaluated as a number.
Public Function IsNumeric(ByVal Expression As Object) As Boolean
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Testing Input to Determine
If the Value Is Numeric
►The Visual Basic IsNumeric function can check
the input value to determine if the value can be
converted into a numeric value such as an
Integer or Decimal data type
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Checking for a Positive Number
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Deploying the Application
►With Visual Studio open and the program you
want to run loaded, click the Start Debugging
button on the Standard toolbar
• If necessary, select Pocket PC 2003 SE
Emulator in the Device list. Click the Deploy
button
►After the Wood Cabinet Estimate application
loads and executes on the emulator device, type
15 in the Linear Feet text box
►Using your mouse, click the Oak radio button,
and then click the Calculate button
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Deploying the Application
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Using the Input Panel
► When you use the emulator, you can enter data directly
from the keyboard
► The Pocket PC has the input panel to enter data into
applications
• You can use a stylus to select the characters from the
input panel.
• When you press the stylus on a character in the input
panel, the
character is entered
into the focused object
on the form
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Closing the Emulator
►When you are finished with the application, close
the emulator by clicking the Close button (X) in
the upper-right corner of the Pocket PC emulator
►It is critical that you click the No button
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Summary
►Write programs for devices other than a personal
computer
►Understand the use of handheld technology
►Write handheld applications for a Personal Digital
Assistant
►Use the Panel object
►Place RadioButton objects in applications
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5
Summary
►Display a message box
►Make decisions using If…Then statements
►Make decisions using If…Then…Else statements
►Make decisions using nested If statements
Chapter 5: Mobile Applications Using Decision Structures
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5
Summary
►Make decisions using logical operators
►Make decisions using Case statements
►Insert code snippets
►Test input to ensure a value is numeric
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Microsoft Visual Basic 2005
CHAPTER 5 COMPLETE
Mobile Applications
Using Decision Structures