VISUAL BASIC 6.0

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• VISUAL BASIC 6.0

Mr. Bimal Kumar Ray LECTURER Dept of Information
Science Telecommunication Ravenshaw
University CUTTACK, ODISHA, INDIA
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Graphical User Interface (GUI) Design

• Should be under users controluser should be
  able to customize
• Form should follow function
• Visually and functionally consistent
• Immediate feedback
• Attempt to prevent user mistakes

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Rapid Application Development (RAD)

• Use of prebuilt objects to make program
  development much faster
• Shorter development life cycles
• Easier maintenance
• Capability to reuse components

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Characteristics or Features of VB

• Provides visual objects (controls) that can be
  drawn onto a window (form)
• Makes building the interface much easier
• Object-oriented code structure
• Code structured around objects
• Easy to understand syntax
• IntelliSense technology helps write code
• Objects can be reused and extended through
  inheritance
• Object -- anything real or abstract, about which
  you store both data and operations that
  manipulate the data
• Class -- an implementation that can be used to
  create multiple objects with the same attributes
  and behavior
• Object is and Instance of a Class

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Characteristics or Features of VB

• Attribute -- identifying characteristics of
  individual objects, such as name or color
• Operation -- an activity that reads or
  manipulates the data of an object called service
  in OOD, in OOP called a method
• Message -- has two parts name of object to which
  message is sent, name of operation that will be
  performed. In OOP called event
• Event-driven language
• Things happen in response to events
• Examples of events mouse click, opening or
  closing a window
• The user, not the program determines the sequence
  of operations

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Program Development Life Cycle (PDLC)

• Methodology
• organized plan that breaks process into steps
• Analyze the problem
• Design the problem
• Code the program
• Test and debug program
• Formalize solution
• Maintain the program

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Basic Introduction

• Properties attributes of objects.
• Controls label,text,check boxes, list boxes,
  combo,listbox etc.
• Forms windows that contain applications
  controls.
• Events messages sent to an object when the
  application runs
• Event procedures in VB written in blocks of code
  called subroutines
• Procedures operations or services.
• include methods, functions, subroutines
• Statement an instruction that can stand alone.
• Code a group of statements.

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Creating Visual Basic Applications

• Create the interface(form)
• Set the properties
• Write the code

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Creating Visual Basic Applications
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Integrated Development Environment (IDE)

• Provides an environment for creating the
  interfaces, writing and testing code, and making
  changes.
• Create controls on a form and adjust their sizes.
• Understand the events, properties, and methods of
  controls.
• Understand how the code and events work in a VB
  program.
• Open and save a VB project.
• Understand the coding mechanics and the naming
  convention.
• Run an executable without the IDE

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Integrated Development Environment (IDE)

• Menu bar provides many menu items
• Examples include File,Edit,view,project,format
  etc menus.
• Toolbar below menu bar
• Provides shortcuts (icons) to the menu bar.
• Toolbox
• Contains various icons representing VB controls.
• Project Explorer Window
• Shows all forms and modules the current project
  contains.
• Properties window
• shows all the properties of the selected object.

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Integrated Development Environment (IDE)

• Design time
• during which you build an application
• When you are placing controls on the form
• When you are writing code in the code window
• Runtime
• during which you use an application
• When the code in your project comes to life,
  responding to events
• Press Start on the Debug menu in the IDE
• Press the F5 key in the IDE
• Press the start button in the IDE

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Coding

• Comments
• Used to provide begin with tick mark () or Rem
• Appear green colour in the coding line
• Line Continue
• If you have to write a long statement, break into
  lines by using the underscore (_) character.

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Interfaces of Visual Basic Objects

• Forms and controls are objects
• Objects have interfaces
• Properties
• typically relate to appearance of objects
• Events
• user or system actions recognized by the object
• Procedures written to handle events
• Methods
• actions that objects are capable of performing

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Properties

• Special types of data associated with object
• Most relate to appearance of objects
• i.e. Label1.BackColor Color.Red
• Some relate to behavior of objects
• i.e. btnNext.Enabled True
• Object and property separated by dot (. period)
• Property must be given a value

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Events

• User or system actions the object recognizes
• i.e. a button has a Click event
• Event procedure
• Procedure written to handle a specific event
• Also called event handler
• Syntax Private Sub ObjectName_Event
• Code surrounded by Sub End Sub
• Private refers to the scope of the procedure
• Object and event separated by underscore
• Examples private sub cmdok_click()...... End sub

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Methods

• Actions objects are capable of performing
• i.e. Me.Close(),print (), unload() etc
• Syntax Object.Method(Parameter List)
• Parameter list arguments passed in to the method
• Parameter list must be enclosed in parentheses,
  even if no parameters are required

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Naming objects

• When naming objects, be descriptive
• Use standard prefixes, i.e. lbl for label, txt
  for text
• Give the object a meaningful name
• i.e. a label with text Name could be lblName
• Change the object name in the Properties window
• Name objects before placing code in the code
  window

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Assignment Statements

• Generate some sort of result
• i.e. moving data from one location in memory to
  another
• Syntax lblmsg.caption Welcome
• Expression on right hand side of equation moved
  to memory location on left hand side
• Most common statements in VB programs

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Completing the Development Cycle

• Program must be compiled into executable
• When you test run your program, the IDE compiles
  and saves the executable
• To run the program
• Double-click the executable
• Use the Run option off the Start menu
• Add the executable to your Start menu

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Toolbox and Properties List
object box
property list
property values
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Tool Box
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Controls in VB

• Label    
• The label is a very useful control for vb, it can
  also be used to display outputs.
• One of its most important properties is Caption.
• it can display text and numeric data .
• You can change its caption in the properties
  window and also at runtime. 
• Backcolor,Forecolor,font,autosize,border style ,
  back style alignment etc

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Controls in VB

• Text Box   
• The text box is the control for accepting input
  from the user as well as to display the output.
• It can handle string (text) and numeric data but
  not images or pictures.
• Name, text,maxlength,multiline,password
  character, font,back color, forecolor etc
• Events are change,click,dblclick,keyup,keypress,
• mouseover, mousedown etc

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Controls in VB

• Command Button 
• The command button is one of the most important
  controls as it is used to execute commands.
• It displays an illusion that the button is
  pressed when the user click on it.
• The most common event associated with the command
  button is the Click event, and the syntax for the
  procedure is
• Private Sub Command1_Click ()
• Statements
• End Sub

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Controls in VB

• Combo Box 
• The function of the Combo Box is also to present
  a list of items where the user can click and
  select the items from the list. 
• the user needs to click on the small arrow head
  on the right of the combo box to see the items
  which are presented in a drop-down list.
• In order to add items to the list, you can also
  use the AddItem method.
• Exp combo1.additem IST

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Controls in VB

•  List Box
• The function of the List Box is to present a list
  of items where the user can click and select the
  items from the list.
• In order to add items to the list, we can use
  the AddItem method.
• Common methods are removeitem,clear,listcout,
• listindex.

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Controls in VB

•  Check Box
• The Check Box control the user  selects or
  unselects an option.
• When the Check Box is checked, its value is set
  to 1 and when it is unchecked, the value is set
  to 0.  
• A user select any number of checkboxes at the
  same time.

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Controls in VB

• Scroll Bars
• Scroll bar in most of the Windows applications. A
  scroll bar is a very important element of a
  software.
• if you have to scroll down or scroll up a page.
• Two types of scroll bars are there in the VB
  environment HScrollBar (Horizontal Scroll Bar)
  and VScrollbar(Vertical Scroll Bar).
• The Value property returns the scroll bar
  position's value.

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Controls in VB

• Scroll Bars
• The Min property sets/returns the minimum value
  of a scroll bar positionThe Max property
  sets/returns the maximum value of a scroll bar
  position.
• The SmallChange property sets/returns the amount
  of change to Value property in a scroll bar when
  the user clicks on a scroll arrow button.
• The LargeChange property sets/returns the amount
  of change to Value property in a scroll bar when
  the user clicks on the scroll bar area.

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Data Types in Visual Basic

• Byte a numerical data types holding less than
  values 256
• Integer holding numbers without a decimal point
  values 32767
• Long - Long integer ( 8 bytes of storage)
• Single holding numbers with a decimal point ( 4
  bytes storage)
• Double - holding numbers with a decimal point ( 8
  bytes storage)
• Decimal - same as double 16 bytes storage
• Currency Dollar amounts
• String - Character and alphanumeric data
  (text/string)
• Char uses two characters
• Object - Any object reference such as Word
  document
• Variant - default, can hold any data type
• Boolean - True or false
• Date - From Jan 1, 100 to Dec 31, 9999

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Variables, Declarations and Constants

• Variables - A variable represents an area of
  storage in the computer's memory.
• - A unique named storage location that contains
  data that changes during program execution.
• Constant - A unique named storage locations that
  contains data that does not change during program
  execution.
• Local variables - declared within a procedure or
  function.
• Global variables - declared in the general
  section of the vb application.
• Scope variables- Scope refers to how widely
  variable is recognized throughout program.

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Variable Declarations

• Declare variables using the Dim or Static
  statements
• Dim statement - value of variable pre reservation
  only until procedure ends
• Static statement - value of variable pre-
  reservation the entire time the application is
  running
• Must give the variable a name
• Syntax Dim variable name As datatype
• Dim is required variable name As is required
  datatype
• Exp Dim x as single
• Defines a variable named x as a single data type

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Variable Declaration Rules

• Must begin with an alphabetic character
• Can begin with letter or underscore, but not a
  number
• Must be unique name with same scope
• Must be variable name less 255 characters
• variable name should not keyword
• (do, while,wend,bold,underline,size etc
  )
• variable name can not contain a period.
• variable name can not contain spaces.

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Declaring Constants

• Some constants are predefined
• Known as system constants
• Examples include True and False
• Others defined and declared before used
• Known as symbolic constants
• Must be declared with Const statement
• Syntax Const constantname As datatype value
• To declare a constant Const x hello
• Defines the constant x and assigns a value
• Const pi As Single pi 3.145
• Const y As Integer y 100

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Scope variable

• The scope is where a variable is visible and
  usable.
• Declared inside a function only within that
  function (local variable)
• Declared outside a function available
  everywhere Except the function (global variables)
• Can use keyword global to make a variable within
  a function have global scope.
• Super global variables available everywhere
  including functions.

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Module-level variables

• A  Module-level variables can be declared with a
  Dim or Private statement at the top of the module
  above the first procedure definition.
• A variable that is recognized among all of the
  procedures on a module sheet is called a
  "module-level" variable.
• A module-level variable is available to all of
  the procedures in that module, but it is not
  available to procedures in other modules.
• A module-level variable remains in existence
  while VB is running until the module in which it
  is declared is edited.
• there is no difference between Dim and Private.
• (Note that module-level variables cannot be
  declared within a procedure.)
• Dim X as Integer ' Module-level
  variable.
• Private Y as Integer ' Module-level
  variable. 

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Control Flow statement

• VB provides two types of control flow statement
• 1) If statement
• 2) Select Case statement
• The If Statement If statement of VB comes in
  various forms are given below
• 1) If..Then Statement
• 2) If..Then..Else Statement
• 3) If..Then..ElseIf Statement
• 4) Nested Ifs

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If..Then Statement

• Def. An If..Then statement tests a particular
  condition if the condition evaluates to true, a
  course-of-action is followed otherwise it is
  ignored.
• Syntax
• If (boolean expression) Then
• statements
• End If

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If..Then Statement

• Example 1
• If (Numgt0) Then
• Print It is a positive number
• End if
• Example 2
• If Text1.Textgt18 Then
• text2.text You are eligible to vote
• End if
• Example 3
• If (no mod 20) Then
• label1.caption It is a even number
• End if

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If..Then..Else Statement

• If..Then..Else statement provides an alternate
  choice to the user i.e. if the condition is true
  then a set of statements are executed otherwise
  another set of statements are executed.
• Syntax
• If (boolean Expression) Then
• VB Statement(s)
• Else
• VB Statement(s)
• End If

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Examples of If..Then..Else

• Example 1
• If Text1.Textgt18 Then
• Print You are eligible to vote
• Else
• Print Sorry, You are not eligible to vote
• End If
• Example 2
• If no Mod 20 Then
• Text2.Text It is an Even Number
• Else
• Text2.TextIt is an Odd Number
• End If

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If..Then..ElseIf Statement

• If..Then..ElseIf statement is used to test a
  number of mutually exclusive cases and only
  executes one set of statements for the case that
  is true first.
• Syntax
• If (Boolean Expression) Then
• Statement(s)
• ElseIf (Boolean Expression 2) Then
• Statement(s)
• ElseIf (Boolean Expression 3) Then
• Statement(s)
• Else
• Statement(s)
• End If

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Example of If..Then..ElseIf

• If (Agelt4) Then
• Print Your rate is free.
• ElseIf (Agelt12) Then
• Print You qualify for the childrens rate.
• ElseIf (Agelt65) Then
• Print You must pay full rate
• Else
• Print You qualify for the seniors rate.
• End If

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Nested Ifs

• A nested If is an if that has another If in its
  ifs body or in its elses body. The nested if
  can have one of the following three forms
• 1. If (expresssion 1) Then
• If (expression 2 ) Then
• Statement 1
• Else
• Statement 2
• End If
• Else
• body-of-else
• End If

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Nested Ifs

• 2. If (expression 1) Then
• body-of-if
• Else
• If (expression 2) Then
• Statement-1
• Else
• Statement-2
• End If

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Nested Ifs

• 3) If (expression 1) Then
• If (expression 2) Then
• Statement-1
• Else
• Statement-2
• End If
• Else
• If (expression 3) Then
• Statement-3
• Else
• Statement-4
• End If
• End If

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Example of Nested Ifs

• If Numgt0 Then
• Print It is a positive number
• Else
• If Numlt0 Then
• Print It is a negative number
• Else
• Print The number is equal to zero
• End If
• End If

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Select-Case Statement

• Select-Case is a multiple branching statement and
  is used to executed a set of statements depending
  upon the value of the expression. It is better to
  use Select-Case statement in comparison to
  If..Then..ElseIf Statement when the number of
  checks are more. There are 3 different forms of
  using Select-Case statements and are given below
  

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Different forms of Select-Case

• 1. Select Case Simplest Form Exact match
• Select Case Expression
• Case Value
• one or more visual basic statements
• Case Value
• one or more visual basic statements
• Case Else
• one or more visual basic statements
• End Select

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Example of Form 1

• Select Case byMonth
• Case 1,3,5,7,8,10,12
• number_of_days31
• Case 2
• number_of_days28
• Case 4,6,9,11
• number_of_days30
• End Select

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Syntax of Form 2

• Select Case Second Form Relational Test
• Select Case Expression
• Case is relation
• one or more visual basic statements
• Case is relation
• one or more visual basic statements
• Case Else
• one or more visual basic statements
• End Select

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Example of Form 2

• Select Case marks
• Case Is lt 50
• Result Fail
• Case Is lt 60
• Result Grade B
• Case Is lt 75
• Result Grade A
• Case Else
• Result Grade A
• End Select

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Third Form of Select Case

• Select Case Third Format Range Check
• Select Case Expression
• Case exp1 To exp2
• one or more visual basic statements
• Case exp1 To exp2
• one or more visual basic statements
• Case Else
• one or more visual basic statements
• End Select

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Example of Form 3

• Select Case Age
• Case 2 to 4 Print Nursery
• Case 4 to 6 Print KG
• Case 6 to 10 Print Primary
• Case Else Print Others
• End Select

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Looping Structures

• VB offers broadly following three types of
  looping structures
• For..Next
• Do Loop
• a) Do While..Loop
• b) Do..Loop While
• c) Do Until..Loop
• d) Do..Loop Until
• While..Wend

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For..Next Statement

• This type of statement is used when the user
  knows in advance how many times the loop is going
  to be executed.
• Syntax
• For ltcounter Variablegtltstart_valgt To ltend_valgt
  Step ltincrement/Decrement Valuegt
• One or more VB Statements
• Next ltcounter Variablegt

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Examples

• Example 1 Generate natural nos from 1 to 100
• For x 1 To 100
• Print x
• Next x
• Example 2 Generate first 20 even nos.
• For no 2 to 40 Step 2
• Print no
• Next no
• Example 3 Generate odd nos from 100 to 30 in a
  list box.
• For x 99 to 31 Step -2
• List1.AddItem(x)
• Next x
• Example 4 Generate table of any number N.
• Nval(text1.text)
• For T 1 To N
• Print N T NT
• Next T

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Do..Loop Structures

• Do While..Loop Do While loop is an entry
  controlled loop in which the condition is placed
  at the entry point. This statement executes the
  statements specified in the body of the loop till
  the condition evaluates to true. The loop may not
  be executed at all the if the condition is
  initially false.
• Syntax
• Do While ltcondition or boolean expressiongt
• One or more VB Statements
• Loop

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Examples

• Example 1
• Do
• num InputBox (Enter a number)
• sum sum num
• Loop While num lt gt 0
• Here the statements inside the loop will be
  executed once no matter what the comparison test
  evaluates to.

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Array

• An array is collection of variables of the same
  type that are referenced by a common name.
• To refer to a particular location or element in
  the array, we specify the array name and the
  array element position number.
• Each index number in an array is allocated
  individual memory space.
• We can declare an array of any of the basic data
  types including variant, user-defined types and
  object variables.
• The individual elements of an array are all of
  the same data type.

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Array

• Declaring array
• Syntax dim ltarray namegt (ltmax index in arraygt)
  as data type
• Dim x (5) As Integer
• In the above examples x is the name of the array,
  and the number 5 included in the parentheses is
  the upper limit of the array. The above
  declaration creates an array with 5 elements,
  with index numbers running from 0 to 4.
•  Dim x (1 To 6) As Integer
• If we want to specify the lower limit, then the
  parentheses should include both the lower and
  upper limit a long with the To keyword.

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Array Example

• Creates array enter a range number print the
  total and their average.
• Private Sub Command1_Click()
• Dim arr(5) As Single, index As Integer, sum As
  Single
• Dim no As Integer
• no InputBox("Enter a range number")
• For index 1 To no
• arr(index) InputBox("enter a number")
• Next
• For index 1 To no
• sum sum arr(index)
• Next
• Print " Total " sum
• Print " The Average is " sum / no
• End Sub

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Functions

• A function is a procedure that performs a
  specific task and returns a value.
• A function procedure is a separate procedure
  that can take arguments, perform a series of
  statements, and change the value of its
  arguments.
• The function will return a value to the calling
  subroutine based on the code that it contains.
• syntax
• Private/public Function fun_name (ByVal
  variable list as datatype) As datatype  
•   body of function
• End Function

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Function Example

• Write a function that received two numbers and
  returns the additions
• Private Function Add (ByVal x as Integer,
  ByVal y as Integer) As Integer
•     Add x y
• End Function   
• Private Sub Command1_Click ()
•    Dim a ,b, c as Integer 
•    a val(text1.text)
• b val(text2.text)
•   c Add (a, b)    
• text3.text c
• End Sub

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LIBRARY FUNCTIONS

• String Function
• Lcase, Ucase, Len, Trim, Ltrim, Rtrim,, Left,
  Right, Mid, asc, Chr, strreverse
• Number Function
• Val, sgn, rnd ,format, int
• Date function
• Now, date, time,day,month,year, hour,minute,
  second

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Subroutine

• A subroutine is like a function, but it does not
  return a value.
• Both a function and a sub (sub for subroutine)
  are blocks of code.
• You can pass parameters to both subs and
  functions.
• Parameters may be passed by value or by
  reference.
• The Function or Subroutine receives a pointer to
  the original variable or object.
• Any changes made in the Subroutine are made
  directly to the original variable or object.

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Writing a Sub Procedure

• Declared with Sub keyword
• Syntax Private/Public Sub SubName(Parameter
  List)
• Private/Public are optional access modifiers
• SubName is any valid name
• Parameter List is a list of parameters
  (arguments) passed to the sub
• Ends with End Sub statement

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Sub Procedure Example

• Write a procedure that received a number and
  checked whether the even or odd number
• Private Sub demo( x As Integer )
• If x Mod 2 0 Then
• MsgBox "this number is even"
• Else
• MsgBox "this number is odd"
• End If
• End Sub
• Sub Command1_Click()
• Dim a As Integer
• a InputBox ("enter any number")
• Call demo (a) ' procedure calling
• End Sub

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Calling a Sub Procedure

• Refer to the Sub by name
• Pass in required arguments (parameters)
• Arguments must be passed in the order given in
  the Sub header
• Arguments must be of same type as specified in
  the Sub header
• It is possible to pass data by parameter name
• Syntax SubName(Parameter1Argument1)
• Parameter1 represents name of parameter
• Argument1 represents argument passed

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Terminating a Procedure Before Reaching the End

• Exit Sub statement terminates a Sub
• Often included inside an If block or loop if you
  want the procedure to end if a certain condition
  is met
• Return statement also terminates the sub
• Control of program returned to calling procedure

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Sub Procedure Modifiers

• Access modifiers declare scope of procedure
• Private procedures recognized only in the current
  form or class
• Public procedures accessible to all modules in
  project
• Parameters contain data the procedure needs to
  perform its task
• ByVal keyword indicates the actual value of
  variable is passed to procedure
• If value is changed by procedure, original value
  of variable is unchanged
• ByRef keyword indicates variable memory address
  is passed to procedure
• If value is changed by procedure, memory address
  is updated

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MDI FORM(Multiple Document Interface)

• MDI application allows us to display multiple
  documents at the same time, with each displayed
  in its own windows.
• MDI applications as they allow opening of several
  documents one bye one at a time.
• MDI allows you to create an application that
  maintains multiple forms within a single
  container form.
• MDI application must have at least two forms, the
  parent form and two or more child forms.
• An MDI application can contain only one MID form
  on a project.
• Any form can be made an MDI child form by setting
  its MDIChild property to true.
• Now add an MDI form to your project by following
  step
• Project-gt Add MDI Form-gtopen.

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To Create Menu Control in The Menu Editor

• Select the form.
• Form the tool menu choose menu editor
• In the caption text box, type the text for the
  first menu title that you want on the menu bar.
• In the name text box type the name, which you
  will use to refer to the menu control code.
• Click on the left/right arrow and button to
  change the label of the control.
• Set the properties of the control if you choose,
  you can do this in the menu editor. Choose next
  to create another menu control.
• You can also click on the up arrow and down arrow
  buttons to move controls along the existing menu
  control.
• Choose OK to close the menu editor.

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Creating Menus with the Menu Editor
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CREATING TOOL BARS

• Toolbars are an extremely useful enhancement to
  menus.
• They provide mouse prevent shotcuts to menu
  options.
• When designing tool bar it is important to
  consider the designed sanitation.
• You may want to use standardized button or
  icons

77
Adding Images to Toolbar

• Now you need to add some images on the toolbar to
  do the followings.
• Add an image list to your form and set its name
  property to image Toolbar.
• This control was added to your toolbox when you
  added the Microsoft common control 6.0.
• Open the property pages dialog box by selecting
  custom from the properties window.
• When the property pages dialog box appears, click
  on the images tab. So you can add some images.

78
Common Dialog Boxes

• The common dialog box in visual basic is an
  insertable control that allows users to display a
  number of common dialog boxes in their program.
• In Visual Basic you can use Dialog boxes for
  common events such as selecting a colour ,font,
  open,save ,print and help.
• Visual Basic displays a dialog box that requests
  more information before the command is carried
  out.
• Displays a message in a dialog box, waits for the
  user to click a button, and then returns an
  integer indicating which button the user clicked.
• To use this control, you must select Microsoft
  Common Dialog Control 6.0 on the Controls tab in
  the Components window.

79
Common Dialog Boxes

• Predefined standard dialog boxes for
• Font and Color selection
• File Opening and Saving
• Printing and Previewing
• select Project -gt Components-gt Microsoft Common
  Dialog Control 6.0 then, the control icon will
  appear in your toolbox and you can add it as a
  form like any other control.
• Use CommonDialog method to display the common
  dialog box at run time
• Code must be written to retrieve and use the
  choice made by the user in the common dialog box

80
Color Dialog Box Coding

• Private Sub cmdColour_Click()
• On Error GoTo errhandler
• CommonDialog1.CancelError True
• CommonDialog1.ShowColor
• Me.BackColor CommonDialog1.Color
• Exit Sub
• errhandler
• Select Case Err
• Case 32755 ' Dialog Cancelled
• MsgBox "you cancelled the dialog box"
• Case Else
• MsgBox "Unexpected error. Err " Err " "
  Error
• End Select
• End Sub

81
Save Dialog Box Coding

• Private Sub cmdSave_Click()
• On Error GoTo errhandler
• CommonDialog1.CancelError True
• CommonDialog1.Flags cdlOFNHideReadOnly
  cdlOFNOverwritePrompt cdlOFNPathMustExist
• CommonDialog1.Filter "All Files (.).RTF
  (.rtf).rtfText Files (.txt).txt
• CommonDialog1.Filename ""
• CommonDialog1.ShowSave
• Text1.Text "File Selected "
  CommonDialog1.Filename
• Exit Sub
• errhandler
• Select Case Err
• Case 32755 ' Dialog Cancelled
• MsgBox "You cancelled the dialog box"
• Case Else
• MsgBox "Unexpected error. Err " Err "
  " Error
• End Select
• End Sub

82
CommonDialog

• Color and Font Dialogs

83
Introduction to Working with Databases in Visual
Basic

• Database
• The storage of different types of data in such a
  way that the data can be easily manipulated and
  retrieved by an end user.
• A database is composed of fields, records, and
  tables.
• Multiple computers can be connected to the same
  database.
• VB can be used to work with existing databases.
• VB provides Microsoft Access database with an
  .mdb extension.
• VB can be used to create a user-friendly
  front-end to a database.

84
The Data Control

• The data control is essential to working with
  databases in VB.
• It uses an internal pointer to point to the
  current record.
• DatabaseName property must be set to the path
  name of the database.
• RecordSource property must be set to the table of
  the database.
• Textboxes and other controls can be bound to a
  data control by assigning their DataSource
  property to the data control.
• The bound controls DataField property is set to
  a field of the DataSource table.
• The Recordset object represents the records in
  the database.

85
RecordSet Methods

• There are several useful methods for the
  Recordset object
• MoveFirst - move to first record
• MoveLast - move to last record
• MoveNext - move to next record
• MovePrevious - move to previous record
• AddNew - add a new record (save by moving to new
  record or using UpdateRecord method)
• Delete - delete current record
• UpdateControls - make bound controls the same as
  database

86
Recordset Properties

• There are main useful properties for the
  Recordset object
• AbsolutePosition - the current position of
  pointer
• RecordCount - the number of records in the
  Recordset
• BOF (EOF) - True if at Beginning (End) of File
• Bookmark - A unique identification of each
  record
• FindFirst - to find first character of a matching
  record
• NoMatch -property is true, no record matches

87
Data Access Objects

• Visual Basic application acts as a front-end to
  the database
• Visual Basic application provides the interface
  between the user and the database
• interface allows the user to tell the database
  what he or she needs
• allows the database to respond to the request
• displaying the requested information in some
  manner

88
Data Access Objects

• A Visual Basic application cannot directly
  interact with a database
• There are two intermediate components between the
  application and the database
• data control
• database engine

89

• The relationship between the data control, its
  two primary properties (DatabaseName and
  RecordSource), and the Recordset object is

90

• The relationships between a data bound control
  (DataSource and DataField properties) and the DAO
  data control (Recordset property) are

91
Jet Database Engine

• Data control
• It connects the application to the database via
  the database engine.
• It is the  connected  between the application and
  the engine, passing information back and front th
  between the two application
• It is a Visual Basic object
• Jet Database Engine
• It is the heart of a Visual Basic database
  management system
• Having this engine saves programmers a lot of
  work.
• The database engine native to Visual Basic is
  known as the
• Jet engine.
• It is the same engine used by Microsoft Access
  for database management.
• it is primarily used to work with Access
  databases, but it can also work with others.
• It requires less code to connect to an existing
  database
• View all information within that database
• Insert, delete, modify any and all information
  within that database

92
Data Access Object (DAO)

• It is a structure of objects for accessing
  databases through your code.
• All the functionality of the Data control is also
  available to your code, through the DAO.
• Record Set
• Record sets are objects that represent
  collections of records from one or more tables.
• You cant access the tables of a database
  directly. The only way to view or manipulate
  records is via RecordSet object.
• A RecordSet is constructed of columns and rows
  and is similar to a table. But it can contain
  data from multiple table.
• Three types of RecordSets are
• DynaSets ? Which are updatable views of data
• SnapShots ? Which are static( read only) views
  of data
• Tables ? Which are direct views of
  tables.

93
DAO Data Control Properties

• Important properties of this data control are
• Caption displayed on the data control.
• Connect Type of database. Default is Microsoft
  Access (or Jet).
• DatabaseName Returns or sets the name of the
  source DB for the data
• control. Must be a
  fully qualified path and file name.
• Exclusive Indicates whether the underlying
  database is opened for single- user or
  multi-user access.
• ReadOnly Indicates whether the data can be
  edited or not.
• Recordset A set of records defined by a data
  controls Connect,
• DatabaseName, and
  RecordSource properties.
• Run-time only.
• RecordsetTypeIndicates type of Recordset you
  want data control to create
• RecordSource Determines the table (or virtual
  table) the data control is attached to.

94
DAO Data Control Recordset Methods

• Important Recordset methods are
• AddNew Adds a new record to the Recordset.
• Update Saves the current contents of all data
  bound controls.
• CancelUpdate Used to cancel any pending updates
• (either with Edit or
  AddNew method)
• Close Closes a Recordset.
• DeleteThe current record is deleted from the
  Recordset.
• Edit Places the current record in the Recordset
  into edit mode.
• Requery Updates the data in a Recordset object
  by re-executing the query on which the object
  is based.
• MoveFirst/ MoveLast/ MoveNext/ MovePrevious
• Moves the current record pointer to the first
  record in the Recordset.

95
DAO Database Connection Examples

• Dim db As Database
• Dim rs As Recordset
• Private Sub Form_Load()
• Set db OpenDatabase("d\bkr1.mdb")
• Set rs db.OpenRecordset("select from sim",
  dbOpenDynaset)
• End Sub
• Private Sub cmdnext_Click()
• rs.MoveNext
• If rs.EOF Then
• rs.MoveFirst
• End If
• Text1.Text rs!roll
• Text2.Text rs!Name
• Text3.Text rs!mark
• End Sub

96
DAO Database Connection Examples

• Private Sub cmdprev_Click()
• rs.MovePrevious
• If rs.BOF Then
• rs.MoveFirst
• End If
• Text1.Text rs!roll
• Text2.Text rs!Name
• Text3.Text rs!mark
• End Sub
• Private Sub cmdnew_Click()
• rs.AddNew
• Text1.Text
• Text2.Text
• Text3.Text
• Text1.setfocus
• End Sub

Private Sub cmdedit_Click() rs.Edit rs!roll
Text1.Text rs!Name Text2.Text rs!mark
Text3.Text rs.Update rs.Bookmark
rs.LastModified Text1.Text "" Text2.Text
"" Text3.Text "" MsgBox "successfully modify
your data", vbInformation End Sub
97
THANK YOU