Visual Basic.NET Programming

January 21, 2004

Class Agenda – January 21, 2004Homework

Open Questions?

Programming Paradigm's

Program Design Tools

Review Homework Assignment

Modular Programming

Visual Basic.NET Language Features

Class ExerciseWrite a Modular Name ListerIntroduction to Windows Forms

Homework

1. Zip entire project

2. Email zip file to me

3. I will acknowledge receipt of homework, probably something as simple as "got it"

4. I tend to send out grades after all assignments are in...

5. If you really want to know send me an email and I'll make a special effort

Questions?

• Concatenation Operators

Concatenation Operators

• & Operator

result = expression1 & expression2

• + Operator

expression1 + expression2

& Operatorresult = expression1 & expression2

• Generates a string concatenation of two expressions.

• If the data type of expression1 or expression2 is not String but widens to String, it is converted to String. If one of the data types does not widen to String, the compiler generates an error.

• The data type of result is String. If one or both expressions are stated as Nothing or have a value of DBNull.value, they are treated as a string with a value of "".

+ Concatenation Operator

expression1 + expression2

• Adds two numbers. Also used to concatenate two strings.

• The value of the result will be the sum of expression1 and expression2 if expression1 and expression2 are numeric or the result of the concatenation of expression1 and expression2 if expression1 and expression2 are strings.

C# String Concatenation

• The binary + operator performs string concatenation when one or both operands are of type string.

• If an operand of string concatenation is null, an empty string is substituted.

• Otherwise, any non-string argument is converted to its string representation by invoking the virtual ToString method inherited from type object. If ToString returns null, an empty string is substituted.

Programming Paradigm's

Programming Paradigms

• Procedural Programming Console Applications (Sequential Flow)

• Procedural Programming (Modular Design)

• Event Driven Programming Windows Forms Applications (Random Flow)

• Object Oriented Programming Combining Data and Procedures into Standalone Components.

Procedural Programming

• Console Applications

• Programs have a sequential flow

• Programmer can anticipate and control logical flow

• Typical– Open a File– Read through a file one record at a time– Process each record– At End Close File

Event Driven Programming

• Windows Applications

• Web Form Applications

• Programs do NOT have a predictable flow to them, but respond to user input (point and click)

• Getting input out of sequence is a design consideration

• Typical– User selects a menu item– User opens a second file and switches between files– User inserts or removes data randomly

Object Oriented Programming

• Combining Data and Procedures into Standalone Components.

• Have to wait a couple of weeks...

Program Design Tools

How To Design a Program

• Pseudocode

• Using a Flow Chart

Pseudocode

• Informal language to helps programmers develop algorithms

• Not executed on computers

• Helps conceptualize a program during the program-design process

• Describes only executable statements

Name Lister Pseudo Code Example

1. Enter First Name (if empty error, try again)

2. Enter Middle Name

3. Enter Last Name (if empty error, try again)

4. Concatinate Name Fields build full name

5. Check Length (if > 20 then shorten full name)

6. Request display type (horizontal or vertical, forward or backward) display accordingly

7. add loops (another display? another name? exit logic...)

Flow Charting

• Flowcharts– Graphical representation of an algorithm– Drawn using certain special-purpose symbols

• Rectangles

• Diamonds

• Ovals

• Small circles

add grade to total

add 1 to counter

total = total + grade

counter = counter + 1

Flowcharting Visual Basic’s sequence structure.

Grade >= 60true Console.WriteLine(“Passed”)

false

Flowcharting a single-selection If/Then structure.

Flowcharting a double-selection If/Then/Else structure

Grade >= 60true Console.WriteLine(“Passed”)false

Console.WriteLine(“Failed”)

So, how do we design programs?

Let's look at the Homework Assignment

Name Lister Console Application

• Sequential Flow (Procedural Programming)

• List Steps– Enter First Name (if empty error, try again)

– Enter Middle Name

– Enter Last Name (if empty error, try again)

– Concatinate Name Fields build full name

– Check Length (if > 20 then shorten full name)

– Request display type (horizontal or vertical, forward or backward) display accordingly

– add loops (another display? another name? exit logic...)

Sequential Name Lister

Code Walkthrough

Modular Programming

Modular Programming• Modules, Sub Procedures and Functions

• Value Types and Reference Types

• Concept of Scope

Introduction

• Divide and Conquer– The best way to develop and maintain a large

program is to construct it from small, manageable pieces.

Modules, Sub Procedures and Functions

• Division of code into procedures– Several motivations to divide code into procedures

• Divide-and-conquer approach makes program development more manageable

• Used to group related procedures so that they can be reused in other projects

• Software reusability between programs

• Avoids the repetition of code in a program

• Should be self-contained

Modules, Sub Procedures and Functions

Boss

Worker1 Worker2 Worker3

Worker4 Worker5

Hierarchical boss procedure/worker procedure relationship.

Functions and Sub Procedures

• Provide the ability to transfer control within a program.• Simplify code sharing, providing an excellent way to

eliminate redundant code.• Maybe called with one or more arguments or with no

arguments at all

Sub Procedures

• Format of a procedure definitionSub procedure-name(parameter-list) declarations and statementsEnd Sub

• Procedure header– The first line is known as the procedure header

• Procedure-name– Directly follows the Sub keyword– Can be any valid identifier – It is used to call this Sub procedure within the program

• Procedure body– The declarations and statements in the procedure definition form

the procedure body

Function Procedures

• Similar to Sub procedures

• One important difference– Function procedures return a value to the

caller

Function Procedures

• Format of a Function procedure definition

Function procedure-name(parameter-list) As return-type

declarations and statements

End Function• Return-type

– Indicates the data type of the result returned from the Function to its caller

• Return expression

– Can occur anywhere in a Function– It returns exactly one value

– Control returns immediately to the point at which that procedure was invoked

Subroutines with Arguments

Sub AnyProcedure(ByRef strTmp as String)

AnyProcedure(“hi there”)

Sub AnyProcedure(ByRef strTmp As String, ByRef iTmp As Integer)

AnyProcedure(“hi there”, 4)

Subroutines with Arguments (continued)

Sub AnyProcedure(ByRef strTmp As String, ByVal iTmp As Integer)

Dim strTmp As String = “Hello World”

Dim iTmp As Integer = 14

AnyProcedure(strTmp, iTmp)

Functions with ArgumentsSub AnyProcedure(ByRef strTmp as String) As String

Dim aString As String

aString = AnyProcedure(“hi there”)

Function AnyProcedure(ByRef strTmp As String, ByRef iTmp As Integer) As String

aString = AnyProcedure(“hi there”, 4)

Function with Arguments (continued)Function AnyProcedure(ByRef strTmp As String,

ByVal iTmp As Integer) As String

Dim strTmp As String = “Hello World”

Dim iTmp As Integer = 14

Dim aString As String

aString = AnyProcedure(strTmp, iTmp)

Value Types and Reference Types

Value Types and Reference Types

• A data type is a value type if it holds the data within its own memory allocation. A reference type contains a pointer to another memory location that holds the data.

• Value types include:

– All numeric data types

– Boolean, Char, and Date

– All structures, even if their members are reference types

– Enumerations, since their underlying type is always Byte, Short, Integer, or Long

• Reference types include:

– String

– All arrays, even if their elements are value types

– Class types, such as Form

Passing ArgumentsPass-by-Value vs. Pass-by-Reference

• Pass-by-value– The program makes a copy of the argument’s

value and passes that copy to the called procedure

• Pass-by-reference– The caller gives the called procedure the ability

to access and modify the caller’s original data directly.

Argument Passing ByVal• If you pass a variable argument by value using the ByVal

keyword, the procedure cannot modify the variable itself.• If the argument is a reference type, you can modify the

members of the object to which it points, even though you cannot replace the object itself.

• You can modify the members of the object. • If the argument is an array variable, you cannot assign a

new array to it, but you can change one or more of its elements. The changed elements are reflected in the underlying array variable in the calling code.

Argument Passing ByRef

• If you pass a variable argument by reference using the ByRef keyword, the procedure can modify the variable itself.

• If the argument is an object variable, you can assign a new object to it. This reassignment also affects the object variable in the calling program.

Concept of Scope

Scope

When a variable is defined (i.e. as in a Dim statement) the computer assigns memory to that variable. When the variable is no longer needed the computer deletes the variable to free up the memory. Scope defines the time a variable is available to a program.

Scope

A variable defined in a Subroutine or in For Next statement will be deleted when the Subroutine or For Next statement is exited.

Variables that need to persist longer than the life of the Subroutine need to be defined outside the Subroutine, at least at the class or module level.

Scope Rules• Possible scopes

– Module scope• Variable declared in a module have module scope, which is

similar to class scope

– Namespace scope• Procedures defined in a module have namespace scope,

which generally means that they may be accessed throughout a project

– Block scope• Identifiers declared inside a block, such as the body of a

procedure definition or the body of an If/Then selection structure, have block scope

– Class scope• Begins at the class identifier after keyword Class and

terminates at the End Class statement

Visual Basic.NET Language Features

Visual Basic.NET Language Features

• Review Data Types

• Logical Operators

• Control Structures

• Assignment Operators

• Exit Statement

• Print and Display Constants

• MessageBox Class

Visual Basic.NET Keywords

AddHandler AddressOf Alias And

AndAlso Ansi As Assembly

Auto Boolean ByRef Byte

ByVal Call Case Catch

CBool CByte CChar CDate

CDec CDbl Char CInt

Class CLng CObj Const

CShort CSng CStr CType

Date Decimal Declare Default

Delegate Dim Do Double

Each Else ElseIf End

Enum Erase Error Event

Exit ExternalSource False Finally

For Friend Function Get

GetType GoTo Handles If

Implements Imports In Inherits

Integer Interface Is Lib

Like Long Loop Me

Mod Module MustInherit MustOverride

MyBase MyClass Namespace New

Next Not Nothing NotInheritable

NotOverridable Object On Option

Optional Or OrElse Overloads

Overridable Overrides ParamArray Preserve

More Visual Basic.NET KeywordsPrivate Property Protected Public RaiseEvent ReadOnly ReDim Region Rem RemoveHandler Resume Return Select Set Shadows Shared Short Single Static Step Stop String Structure Sub SyncLock Then Throw To True Try TypeOf Unicode Until When While With WithEvents WriteOnly Xor #Const #If...Then...#Else - -= &

&= * *= / /= \ \= ^ ^= + += = The following are retained as keywords, although they are no longer supported in Visual Basic.NET Let Variant Wend

Revisit Data Types• Integers

– Int16 (Short)– Int32– Int64 (Long)

• Boolean

• Floating Point– Single Word (32 bit)– Double Word (64 bit)

• Char and Byte

• Decimal

• String

Integer Data Types

Integer variables are stored as signed 32-bit (4-byte) integers ranging in value from -2,147,483,648 through 2,147,483,647.

The Integer data type provides optimal performance on a 32-bit processor, as the smaller integral types are slower to load and store from and to memory. (Int32)

Short variables are stored as signed 16-bit (2-byte) integers ranging in value from -32,768 through 32,767. (Int16)

Long variables are stored as signed 64-bit (8-byte) integers ranging in value from -9,223,372,036,854,775,808 through 9,223,372,036,854,775,807. (Int64)

Boolean

Dim bTmp As Boolean

bTmp = True

Dim bTmp As Boolean = False

Boolean variables are stored as 16-bit (2-byte) numbers, but they can only be True or False. Use the keywords True and False to assign one of the two states to Boolean variables.

Floating Point Data Types

Single variables are stored as signed IEEE 32-bit (4-byte) single-precision floating-point numbers ranging in value from -3.4028235E+38 through -1.401298E-45 for negative values and from 1.401298E-45 through 3.4028235E+38 for positive values. Single-precision numbers store an approximation of a real number.

Double variables are stored as signed IEEE 64-bit (8-byte) double-precision floating-point numbers ranging in value from -1.79769313486231570E+308 through -4.94065645841246544E-324 for negative values and from 4.94065645841246544E-324 through 1.79769313486231570E+308 for positive values.

Char and Byte Data Types

•Char - Char variables are stored as unsigned 16-bit (2-byte) numbers ranging in value from 0 through 65535. Each number represents a single Unicode character. Direct conversions between the Char data type and the numeric types are not possible, but you can use the AscW and ChrW functions for this purpose.

•Byte - Byte variables are stored as unsigned 8-bit (1-byte) numbers ranging in value from 0 through 255.

Decimal Data TypeDecimal variables are stored as signed 128-bit (16-byte) integers scaled by a variable power of 10. The scaling factor specifies the number of digits to the right of the decimal point; it ranges from 0 through 28. With a scale of 0 (no decimal places), the largest possible value is +/-79,228,162,514,264,337,593,543,950,335. With 28 decimal places, the largest value is +/-7.9228162514264337593543950335, and the smallest nonzero value is +/-0.0000000000000000000000000001 (+/-1E-28).

Appending the literal type character D to a literal forces it to the Decimal data type. Appending the identifier type character @ to any identifier forces it to Decimal. You might need to use the D type character to assign a large value to a Decimal variable or constant, as the following example shows:

Dim BigDec1 As Decimal = 9223372036854775807 ' No overflow. Dim BigDec2 As Decimal = 9223372036854775808 ' Overflow. Dim BigDec3 As Decimal = 9223372036854775808D ' No overflow.

This is because without a literal type character the literal is taken as Long, and the value to be assigned to BigDec2 is too large for the Long type.

Logical Operators

Logical Operators

• Used to form complex conditions by combining simple ones– Short-circuit evaluation

• Execute only until truth or falsity is known

– AndAlso operator• Returns true if and only if both conditions are true

– OrElse operator• Returns true if either or both of two conditions are true

Logical Operators without short-circuit evaluation

• And and Or– Similar to AndAlso and OrElse respectively– Always execute both of their operands– Used when an operand has a side effect

• Condition makes a modification to a variable

• Should be avoided to reduce subtle errors

• Xor– Returns true if and only if one operand is true and the

other false

Logical Negation

Not– Used to reverse the meaning of a condition– Unary operator

• Requires one operand

– Can usually be avoided by expressing a condition differently

AndAlso Logical Operator

expression1 expression2 expression1 AndAlso expression2

False False False

False True False True False False True True True

OrElse Logical Operator

expression1 expression2 expression1 OrElse expression2 False False False

False True True True False True True True True

Xor Logical Operator

expression1 expression2 expression1 Xor expression2

False False False

False True True True False True True True False

Not Logical Operator

expression Not expression False True

True False

Precedence and associativity of the operators discussed so far.

Operators Associativity Type () left to right parentheses

^ left to right exponentiation + - left to right unary prefix * / left to right multiplicative \ left to right Integer division Mod left to right modulus + - left to right additive & left to right concatenation < <= > >= = <> left to right relational and equality Not left to right logical NOT And AndAlso left to right boolean logical AND Or OrElse left to right boolean logical inclusive OR Xor left to right boolean logical exclusive OR

Rules of Precedence

• There are 18 (or 13?) Rules of Precedence which can actually be reduced to 2.

1. Multiply / Divide before you Add / Subtract

2. Put ()'s around everything

Control Structures

Control Structures

• Transfer of control

• Selection Structures

• Repetition Structures

Transfer of control

• GoTo statement

It causes programs to become quite unstructured and hard to follow.

Selection Structures

• If/Then– Single-selection structure

• If/Then/Else– Double-selection structure

• If/ElseIf/ElseIf.../Else– Multiple-selection structure

• Select Case– Multiple-selection structure

Select Case Statements• More Elegant Than the If Else Construct• Begin with the words Select Case followed by the

name of the target variable• For each value or range of values for the target

variable a separate case in listed.• Each case begins with the word Case followed by

a specific value or range of values for that case.• Following each Case statement is one of more

lines of code to be executed if that case is true.• An Else Case is often provided to catch any cases

that do not match the target variable.• End with the words End Select

Case Statement Syntax

Dim strTmp As String

'….

Select Case strTmp

Case “add”

some code

Case “delete”

some code

Else Case

perhaps an error message

End Select

Case Statement

Dim Number As Integer = 8' ...Select Case Number ' Evaluate Number.

Case 1 To 5 ' Number between 1 and 5, inclusive.Debug.WriteLine("Between 1 and 5")

' The following is the only Case clause that evaluates to True.Case 6, 7, 8 ' Number between 6 and 8.

Debug.WriteLine("Between 6 and 8")Case 9 To 10 ' Number is 9 or 10.

Debug.WriteLine("Greater than 8") Case Else ' Other values.

Debug.WriteLine("Not between 1 and 10")End Select

Repetition Structures

• For/Next

• For Each/Next

• While

• Do While/Loop

• Do/Loop While

• Do Until/Loop

• Do/Loop Until

Essentials of Counter-Controlled Repetition

• Elements needed– Control variable

• Used to determine whether loop continues to iterate

– Initial value of control variable– Increment (or decrement)

• Describes how control variable is modified during each iteration

– Condition• Tests for final value of control variable

For/Next Counter-Controlled Repetition

• Structure header initializes control variable, specifies final value and increment– For keyword begins structure

• Followed by control variable initialization– To keyword specifies final value– Step keyword specifies increment

• Optional

• Increment defaults to 1 if omitted

• May be positive or negative• Next keyword marks end of structure

• Executes until control variable greater (or less) than final value

For/Next Repetition Structure

For counter = 2 To 10 Step 2

For keyword

Initial value of control variable

Final value of control variable Increment of

control variable

Control variable name

To keyword

Step keyword

While...End While Statements• Executes a series of statements as long as a given condition is

True.

While condition [ statements ]

End While

• If condition is True, all of the statements are executed until the End While statement is encountered. Control then returns to the While statement and condition is again checked. If condition is still True, the process is repeated.

• If condition is False, execution resumes with the statement following the End While statement.

• You can nest While loops by placing one loop within another.

Assignment Operators

Assignment Operators

• Binary operators– +, -, *, ^, &, / or \

variable = variable operator expression

variable operator= expression

• Example– Addition assignment operator, +=

value = value + 3

value += 3

Assignment Operators

Assignment operator

Sample expression

Explanation Assigns

Assume: c = 4, d = "He"

+= c += 7 c = c + 7 11 to c -= c -= 3 c = c - 3 1 to c *= c *= 4 c = c * 4 16 to c /= c /= 2 c = c / 2 2 to c \= c \= 3 c = c \ 3 1 to c ^= c ^= 2 c = c ^ 2 16 to c &= d &= "llo" d = d & "llo" "Hello" to d

Exit Statement

Using the Exit Keyword in a Repetition Structure

• Exit Statements– Alter the flow of control

• Cause immediate exit from a repetition structure

– Exit Do• Executed in Do structures

– Exit For• Executed in For structures

– Exit While• Executed in While structures

Print and Display Constants

Print and Display ConstantsMember Constant Equivalent Description

CrLf vbCrLf Chr(13) + Chr(10) Carriage return/linefeed character combination.

Cr vbCr Chr(13) Carriage return character.

Lf vbLf Chr(10) Linefeed character.

NewLine vbNewLine Chr(13) + Chr(10) New line character.

NullChar vbNullChar Chr(0) Character having value 0.

na vbNullString String having value 0 Not the same as a zero-length string (""); used for calling external procedures.

na vbObjectError -2147221504 Error number. User-defined error numbers should be greater than this value. For example: Err.Raise(Number) = vbObjectError + 1000

Tab vbTab Chr(9) Tab character.

Back vbBack Chr(8) Backspace character.

FormFeed vbFormFeed Chr(12) Not useful in Microsoft Windows.

VerticalTab vbVerticalTab Chr(11) Not useful in Microsoft Windows.

Quote na Chr(34) Quotation mark character (" or ') used to enclose values.

MessageBox

MessageBox Class

Displays a Dialog box that can contain text, buttons, and symbols to inform and instruct the

user.

MessageBox.Show Method (String, String, MessageBoxButtons, MessageBoxIcon) 

Displays a message box with specified text, caption, buttons, and icon.

MessageBox.Show(text As String, caption As String, buttons As MessageBoxButtons, icon As MessageBoxIcon) As DialogResult

Parameters

text - The text to display in the message box.

caption - The text to display in the title bar of the message box.

buttons - One of the MessageBoxButtons values that specifies which buttons to display in the message box.

icon - One of the MessageBoxIcon values that specifies which icon to display in the message box.

Return Value

One of the DialogResult values.

MessageBox ButtonsMessageBoxButton constants Description

MessageBoxButton.OK OK button. Allows the user to acknowledge a message. Included by default.

MessageBoxButton.OKCancel OK and Cancel buttons. Allow the user to either continue or cancel an operation.

MessageBoxButton.YesNo Yes and No buttons. Allow the user to respond to a question

MessageBoxButton.YesNoCancel Yes, No and Cancel buttons. Allow the user to respond to a question or cancel an operation.

MessageBoxButton.RetryCancel Retry and Cancel buttons. Typically used to allow the user to either retry or cancel an operation that has failed.

MessageBoxButton.AbortRetry- Ignore

Abort, Retry and Ignore buttons. When one of a series of operations has failed, these butons allow the user to abort the entire sequence, retry the failed operation or ignore the failed operation and continue..

MessageBox IconsMessageBoxIcon Constants Icon Description

MessageBoxIcon.Exclamation Icon containing an exclamation point. Typically used to caution the user against potential problems.

MessageBoxIcon.Information Icon containing the letter "i." Typically used to display information about the state of the application.

MessageBoxIcon.Question Icon containing a question mark. Typically used to ask the user a question.

MessageBoxIcon.Error Icon containing an in a red circle. Typically used to alert the user of errors or critical situations.

Abort - The return value is Abort (usually sent from a button labeled Abort).

Cancel - The return value is Cancel (usually sent from a button labeled Cancel).

Ignore - The return value is Ignore (usually sent from a button labeled Ignore).

No - The return value is No (usually sent from a button labeled No).

None - Nothing is returned from the dialog box. This means that the modal dialog continues running.

OK - The return value is OK (usually sent from a button labeled OK).

Retry - The return value is Retry (usually sent from a button labeled Retry).

Yes - The return value is Yes (usually sent from a button labeled Yes).

Dialog Result - Specifies identifiers to indicate the return value of a dialog box.

MessageBox Sample Code Dim strMessage As String = "No server name. Cancel operation?" Dim strCaption As String = "No Server Name Specified" Dim iBttns As Integer = MessageBoxButtons.YesNo Dim iIcon As Integer = MessageBoxIcon.Question Dim Result As DialogResult 'Displays a MessageBox using the Question icon and specifying the No button as the default. Result = MessageBox.Show(strMessage, strCaption, iBttns , iIcon) ' Gets the result of the MessageBox display.  If Result = DialogResult.Yes Then Me.Close() ' Closes the parent form.  End If

Class ExerciseWrite a Modular Name Lister

Application

Name Lister Modular Code

• Transition from a Sequential to a Modular Design Structure

• Console or Windows Form if your adventurous!

• Remove GoTo Statements

• Add Functions and Subroutines

• Use While End While blocks

• Add a Select Case statement

• Use a MessageBox for errors plus the two loop questions (another display? and another name?)

Introduction to Windows Forms

Introduction to Windows Forms

• Windows Form

• Using ToolBox to add Controls to Form

• Label Control

• Button

• Using F1 or Search for Help

What Are Controls?

• Controls are things like TextBoxes, Buttons, and Labels that you use to build a form.

• When you create Windows Form project the IDE provides a blank form.

• Controls are added to the form to provide functionality

What are properties?

• Forms Have Properties

• Controls Have Properties

• Properties are used to specify controls.

• Text Boxes have Font properties

• Fonts have size and color and bold and …

• Labels have a Text property to describe the label

What About Events?

• When you click on a button the IDE automatically creates a method where you can write the code you wish executed when the button is pushed. This event is called an On_Click event.

Windows Form

A Couple of Properties• ActiveForm points to current form• BackColor Property sets background color

To set a BackColor:ActiveForm.BackColor = Color.Red

To Test For a BackColor:ActiveForm.BackColor.Equals(Color.Red)

Windows Controls

Windows Controls

• Label Control

• Button Control

• RadioButton Control

• GroupBox Control

• ComboBox Control

Using ToolBox to add Controls to Form

• Showing the ToolBox

• Selecting a Control

• Configuring the Control

Label Control

Windows Forms Label controls are used to display text or images that cannot be edited by the user, but can be edited dynamically by the programmer.

–BackColor defaults to Form–ForeColor

Label1.ForeColor = Color.White

Note: Font changes must be made directly to the control on the form.

Button Control

The Windows Forms Button control allows the user to click it to perform an action.

Button1.Text = “Push Me”

Button1.BackColor = Color.Blue

Button1.ForeColor = Color.Yellow

RadioButton Control

Windows Forms RadioButton controls present a set of two or more mutually exclusive choices to the user. While radio buttons and check boxes may appear to function similarly, there is an important difference: when a user selects a radio button, the other radio buttons in the same group cannot be selected as well. In contrast, any number of check boxes can be selected. Defining a radio button group tells the user, "Here is a set of choices from which you can choose one and only one."

When a RadioButton control is clicked, its Checked property is set to true and the Click event handler is called. The CheckedChanged event is raised when the value of the Checked property changes. If the AutoCheck property is set to true (the default), when the radio button is selected all others in the group are automatically cleared. This property is usually only set to false when validation code is used to make sure the radio button selected is an allowable option. The text displayed within the control is set with the Text property, which can contain access key shortcuts. An access key allows a user to "click" the control by pressing the ALT key with the access key.

GroupBox Control

Windows Forms GroupBox controls are used to provide an identifiable grouping for other controls. Typically, you use group boxes to subdivide a form by function. For example, you may have an order form that specifies mailing options such as which overnight carrier to use. Grouping all options in a group box gives the user a logical visual cue, and at design time all the controls can be moved easily — when you move the single GroupBox control, all its contained controls move, too.

RadioButtons in a GroupBox

Sample Code If RadioButton1.Checked Then

Label6.Text = Label5.Text ' Horizontal Forward

ElseIf RadioButton2.Checked Then

For i = Label5.Text.Length - 1 To 0 Step -1 ' Horizontal Reversed

Label6.Text = Label6.Text + Label5.Text.Substring(i, 1)

Next i

ElseIf RadioButton3.Checked Then ' Vertical Forward

For i = 0 To Label5.Text.Length - 1

Label6.Text = Label6.Text + Label5.Text.Substring(i, 1) + vbCrLf

Next i

ElseIf RadioButton4.Checked Then

For i = Label5.Text.Length - 1 To 0 Step -1 ' Vertical Reversed

Label6.Text = Label6.Text + Label5.Text.Substring(i, 1) + vbCrLf

Next i

Else

MessageBox.Show("No Radio Button Checked!", "Missing Radio Button", MessageBoxButtons.OK, MessageBoxIcon.Warning)

End If

ComboBox Control

• ComboBox– Combines TextBox features with drop-down

list– Drop-down list

• Contains a list from which a value can be selected

• Scrollbar appears if necessary

ComboBoxes

ComboBoxesComboBox events and properties

Description / Delegate and Event Arguments

Common Properties

DropDownStyle Determines the type of combo box. Value Simple means that the text portion is editable and the list portion is always visible. Value DropDown (the default) means that the text portion is editable, but the user must click an arrow button to see the list portion. Value DropDownList means that the text portion is not editable and the user must click the arrow button to see the list portion.

Items The collection of items in the ComboBox control.

MaxDropDownItems Specifies the maximum number of items (between 1 and 100) that the drop-down list can display. If the number of items exceeds the maximum number of items to display, a scrollbar appears.

SelectedIndex Returns the index of the selected item. If there is no selected item, -1 is returned.

SelectedItem Returns a reference to the selected item.

Sorted Indicates whether items are sorted alphabetically. Setting this property’s value to True sorts the items. Default is False.

Common Event (Delegate EventHandler, event arguments EventArgs)

SelectedIndexChanged

Generated when the selected index changes (such as when a different item is selected). This is the default event when control is double-clicked in designer.

ComboBoxes

ComboBoxes

Sample Code To Access Value

If no value is selected from a ComboBox the value of ComboBox.Text = “”

Otherwise the selected value is in ComboBox.Text

Sample Code – To Insert

Dim i As Integer

Dim bFound As Boolean = False

iAdded = Label5.Text.Length / 2

For i = 0 To ComboBox1.Items.Count - 1

If ComboBox1.Items(i) = iAdded.ToString Then

bFound = True

Exit For

End If

Next

If Not bFound Then

ComboBox1.Items.Add(iAdded.ToString)

End If

'ComboBox1.Sorted = True

Sample Code – To Remove

For i = 0 To ComboBox1.Items.Count - 1

If ComboBox1.Items(i) = iAdded.ToString Then

ComboBox1.Items.RemoveAt(i)

Exit For

End If

Next i

iAdded = 0

Using F1 or Search for Help

• To Use Visual Studio.NET Help function, you can either:– Place the cursor on the control or command in

question and type an F1

or– Bring up the Help Search Window

Help Search– Enter the desired topic

In Class Exercise

Write a Windows Form Version of the Name Lister Program

More Windows Controls

The Use of Date and Time

• DateTime Data Type

• DateTimePicker and Timer Controls

• Format and DateDiff Functions

• Class Problem 2 / Clock Program

DateTime Data Type

• DateTime Structure

• Represents an instant in time, typically expressed as a date and time of day.

DateTime Member Functions

• NowDim today As DateTime = Now

• Year, Month, Day, Hour, Minute, SecondDim Year As Integer = today.YearDim Minute As Integer = DateTime.Now.Minute

• DateTime.Now.ToLongDateStringLabel5.Text = DateTime.Now.ToLongDateString

• DateTime.Now.ToLongTimeStringLabel5.Text = DateTime.Now.ToLongTimeString

DateTimePicker Control

• Tool for Selecting a Date

• Returns Date Selected in DateTime format

DateTimePicker Control

The Windows Forms DateTimePicker control allows the user to select a single item from a list of dates or times. It appears in two parts: a drop-down list with a date or time represented in text, and a grid that appears when you click on the down-arrow next to the list. The grid looks like the MonthCalendar control, which can be used for selecting multiple dates.

DateTimePicker Sample Code

difHours = DateDiff("h", DateTimePicker1.Value, DateTimePicker2.Value)

Timer Control

The Windows Forms Timer is a component that raises an event at regular intervals. This component is designed for a Windows Forms environment.

Timer Control Sample Code

• Timer Properties

– Enabled True or False

– Interval The number of milliseconds between each timer tick. The value is not less than one. To get the number of seconds in the interval, divide this number by 1,000.

Private Sub Timer1_Tick(ByVal sender As System.Object,

ByVal e As System.EventArgs)

Handles Timer1.Tick

Label3.Text = DateTime.Now.ToLongTimeString

Label5.Text = DateTime.Now.ToLongDateString

End Sub

Format Function

Returns a string formatted according to instructions contained in a format String

expression.

Note: The String.Format method also provides similar functionality.

Sample Number Formatting Code

MyStr = Format(23) ' Returns "23" ' User-defined numeric formats.MyStr = Format(5459.4, "##,##0.00") ' Returns "5,459.40".MyStr = Format(334.9, "###0.00") ' Returns "334.90".MyStr = Format(5, "0.00%") ' Returns "500.00%".

Label10.Text = Format(difDays, "###,##0.00") difDays is a Double Label9.Text = Format(difWeeks, "###,##0.00") difWeeks is a Double

Sample Date Formating Code

Dim MyDateTime As Date = #1/27/2001 5:04:23 PM#Dim MyStr As String' Returns current system time in the system-defined long time formatMyStr = Format(Now(), "Long Time")' Returns current system date in the system-defined long date formatMyStr = Format(Now(), "Long Date")' Also returns current system date in the system-defined long date ' format, using the single letter code for the formatMyStr = Format(Now(), "D")' Returns the value of MyDateTime in user-defined date/time formatsMyStr = Format(MyDateTime, "h:m:s") ' Returns "5:4:23"MyStr = Format(MyDateTime, "hh:mm:ss tt") ' Returns "05:04:23 PM"MyStr = Format(MyDateTime, "dddd, MMM d yyyy") ' Returns "Saturday, ' Jan 27 2001"MyStr = Format(MyDateTime, "HH:mm:ss") ' Returns "17:04:23“

DateDiff Function

Returns a Long value specifying the number of time intervals between two

Date values.

Sample Date Diff Code

Dim difHours As Long

difHours = DateDiff("h", DateTimePicker1.Value, DateTimePicker2.Value)

Can also use:“h” result in hours

Enumeration value Unit of time difference

String

DateInterval.DayOfYear y Day

DateInterval.Day d Day

DateInterval.Hour h Hour

DateInterval.Minute n Minute

DateInterval.Month m Month

DateInterval.Quarter q Quarter

DateInterval.Second s Second

DateInterval.Weekday w Week

DateInterval.WeekOfYear ww Calendar week

DateInterval.Year yyyy Year

In Class Exercise

Clock Program

Homework Assignment