III BCA Vb.net Online notes

Components of .net framework

        .Net framework provides multiple advantages to the programmers in comparison to the advantages provided by other platforms. Micro-soft has integrated various modern as well as existing technologies of application development in .net frame work. These technologies are highly efficient for modern as well as future business application. There are following components of .net framework

11.  .net class library

22. Common language run time

33.Dynamic language run time

44.Application domains

55..net frame work security

66. Cross language interoperability

77.Side by side execution

88.Common type system

1..net class library

        .net frame work contains multiple classes that are readily available for developers. The class in the FCL (frame work class library) are grouped under multiple namespaces

2.Common language run time

        CLR provides interoperability between different languages, like C#, VB, Visual C++ by providing a common environment for the execution of code orientation of these languages.

3.Dynamic language runtime

        DLR provides to execute dynamic language on .net frame work by adding some special services to the CLR

 

4. Applications domains

        It is used to isolate the process of different applications and can be defined by .net frame work.

5. .net frame work security

        .net frame work provides multiple tools that can be used by developers to protect the resources and code from unauthorized users.

6.Cross language interoperability

        Object or compiled code of one language can be used in other .net compatible language

7. side by side execution

        In some application we can use multiple versions of CLR simultaneously.

 

8.Common type system

    CTS is used to maintain data integrity across the code written in different.net compliant languages CTS also used to present data loss when a type in one language transfers data to its equivalent type in other languages.

Directives

        The vb.net compiler directives give instructions to the compiler to pre-process the information before the actual compilation starts. All these directives begin with #, and only white space characters may appear before a directive on a line. These directives are not statements.

          Vb.net compiler does not have a separate preprocessor. However, the directives are processed as if there was one.

        Vb.net provides the following set of compiler directives.

-        The # const Directive

-        The # external source directive

-        The #if … then… # else directives

-        The # region directive

 

The #const Directive

        This directive defines conditional compiler constants.

#const const name = expression

Const name – specifies the name of the constant required.

#const state =” Tamil Nadu”

        The following code demonstrates a hypothetical use of the directive

Module module1

#const age=true

Sub main()

#if age then

Console.WriteLine(“you are welcome to the robotics club”)

#end if

 Console.ReadKey()

End sub

End module

The #External source directive

        The directive is used for indicating a mapping between specific lines of source code and text external to the source.

#External source (“c:\directives.vb”0

Console.writeline “This is the external code”

#end external source

 

The #if… then… else Directives

        The Directive conditionally compiles selected blocks o code.

#const targetos=”linux”

#if targeros =”windows 7” then

Windows 7 specific code

#else if targetos =”windows xp” then

Windows xp specific code

#else

 Code for other OS

#end if

 

# region directive

        The directive helps in collapsing and hiding sections of code.

#region

        

Track bar control

        The track bar control resembles the scroll bar because it provides a slider, analogous to the thumb of the scroll bar, for the user to position with the mouse or keyboard. The relative position of the slider is exposed as the value of the control. Unlike the scroll bar, there are no separate horizontal and vertical versions of the trackbar control. Instead, an orientation property can have the value of either horizontal or vertical. You can also change the background color using the back color property.

        A horizontal track bar is similar to a horizontal scroll bar in that the value property increases as the slider is moved from left to right. In contrast, the vertical track bar is opposite the vertical scroll bar, the value of a vertical scroll bar increases from top to bottom, but the value of a vertical scroll bar increases from top to bottom, but the value of a vertical track bar increases from bottom to top. This makes sense if you think about the primary use of the two controls a scroll bar is usually used for positioning, but a track bar is generally used for setting a value.

An accessible name is the name of a user interface element. Its value is a big part of what is communicated to users of assistive technology. Without it, people who rely on those technologies would have difficulty understanding or interact with much of the content on the page.

The AccessibleRole property describes what kind of user interface element an object is. If the control's role cannot be determined, the AccessibleRole property is set to Default. For more information about the properties of accessible objects

the cursor is an indicator used to show the current position for user interaction on a computer monitor or other display device

Orientation: sets a value indicating the horizontal or the vertical orientation of the track bar.

Small change: sets the value added to or subtracted from the Value property when the track bar is moved a small distance.

Tick frequency:   if the range is from 0 to 10, and the Tick Frequency is 2, there will be one tick for every 2 increments in the range.

 

Tick style:  sets a value indicating how to display the tick marks on the track bar.

Allow drop: sets a value indicating whether this element can be used as the target of a drag-and-drop operation.

Autosize: automatically adjust the height to fit the text.

A context menu is a pop-up menu that provides shortcuts for actions, the software developer anticipates the user might want to take.  

Large change: sets the value added to or subtracted from the Value property when the track bar is moved a large distance

Tab index: The element can be focused by pressing the Tab key

ADO.NET

        ADO.NET is a data access technology from a micro soft .net framework, which provides communication between relational and non-relational systems through a common set of components. ADO.NET uses built for a disconnected architecture, so it enables truly disconnected data access and data manipulation through its data set. Object, which is completely independent from the data source.

The four objects from the .NET frame work provide the functionality of data providers in the ADO.NET. They are connection object, command object, Data Reader object and data adapter object.

        The connection object provides physical connection to the data source. 

The command object uses to perform SQL statement or stored procedure to be executed at the data source. The data reader object is a stream based, forward only read the only retrieval of query results from the data source. Which do not update the data. Finally, the data adapter object, which populate a data set object which results from a data source. The data adapter object provides a bridge between the data set and the data source.

Advantages:

Ability to cross: Communicate between heterogeneous environments.

        ADO.NET has the exceptional benefit of establishing a connection between two heterogeneous environments. Once the connection is established ADO.NET could easily communicate between these two heterogenous environments.

        Easily scalable: ADO.NET is highly scalable, which means of requirement appear, it is flexible enough to be expanded easily.

High in productivity:
ADO.NET is capable enough to build robust applications.

Performance: There is no lacking or delay and it can set connections quickly to fetch data.

 Applications communicate with a data base, firstly, to retrieve the data stored there and present it in a user-friendly way and secondly, to update the data base by inserting, modifying and deleting data.

        Micro soft Active X data objects .net (ADO.NET) is a model, a part of the .NET frame work that is used by the .NET applications for retrieving, accessing and updating data.

 Data set is an in-memory representation of data. It is a disconnected, cached set of records that are retrieved from the data base.

Components of database

Data table collection

        It contains all the tables retrieved from the data source.

Data Relation collection

        It contains relationships and the links between tables in a data set.

Extended properties

        It contains additional information like the SQL statement for retrieving data, time of retrieval etc.

Data table

        It represents a table in the data table collection of data set. It consists of the data row and data column objects.

Data relation: It represents a relationship in the data relationship collection of the data set.

Data row collection: It contains all the rows in the data table.

Data view:

    It represents a fixed customized view of a data table for sorting, filtering, searching editing and navigation

Primary key

        It represents the column that uniquely identifies a row in a data table.

Data row

        It represents a row in the data table

Data column collection

        It represents all the columns in the data table.

Data column

        It consists of the number of columns that comprise a data table.

ADO.NET Connection String

        Connection string is a normal string representation which contains data base connection information to establish the connection between data base and the application. The connection string includes parameters such as the name of the driver, driver name and data base name as well as security information such as user name, as well as security information such as user name and password. Data providers use a connection string containing a collection of parameters to establish the connection with the data base.

        You can connect your vb.net application to data in a SQL server database using the micro soft .net frame work data provider for SQL server. The first step in a vb.net application is to create an instance of the server object and to establish its connection to an instance of SQL server.

        The SQL connection object is handling the part of physical communication between the application and the SQL server database. An instance of the SQL connection class in .NET framework is supported the data provider for SQL server data base. When the connection is established SQL Commands may be executed, with the help of the connection object, to retrieve or manipulate data in the data base. Once the data base activities over, connection should be closed and release the data base resources. 

The close () method in SQL connection class is used to close the data base connection. The close method roll back any pending transactions and releases the connection from the SQL server database.

System.Data.sqlclient  name space is the .net data provider for sql server.

System.Data.oracleClient         namespace is the .NET frame work data provider for oracle.

System.Data.oledb name space is the .net frame work data provider for OLE db.

System.Data.odbc  name space is the .NET frame work data provider for ODBC.

Connection: connection object provide physical connection to the data source.

Command object: perform SQL statement to be executed at the data source.

The Data reader: sequentially read data

Data adapter: bridge between the data set and the data source.

Data set: disconnected set of records that are retrieved from the data base.

Rich text box

        The rich text box allows formatting the text, it also provides the facility to save the text in the file. Drag and drop rich text box control from the tool box on the window form

        Allows entry and editing of text using advanced formatting features such as paragraph formatting with left and right indents, hanging indents, bold and italic font and so on. Also supports object embedding using the OLE objects collection.

        Rich text box does not have 64 k character limit of ordinary text box controls, plus it also handles drag and drop from both the clipboard and OLE with mouse button behaviour like micro soft word

File name [load from]: the filename of the .txt or .rtf

                                         File loaded into the rich text box

Enabled :   true or false, true means the

                  Object can respond to user generated events

Mouse pointer: The type of mouse pointer displayed

                         When over the rich text box

Scroll bars:  No scroll bars, horizontal, vertical or both

Font              choose a font installed on this system. It’s

              Wise to choose standard windows fonts such

             as MS scans serif that are universally available

             size of font, bold, italic, underline and strike out

Mouse Icon:   custom icon to use when the mouse

                  Pointer property is set to 99

Tool tip text: sets the string to use as a tool tip for this

                       control. Dynamically modified tool tips

WordWrap:If WordWrap property is true, the text in the RichTextBox control automatically wraps to the next line if required. If this property is set to true, horizontal scroll bars are not displayed regardless of the Scroll Bars property setting.

FileRich text box methods

Find     finds text within the control

Load file     loads a text file or existing data stream into

                   the control

paste         pastes the contents of the clipboard into the

                   control

redo           reapplies the last operation

Save File    saves the contents of the control to a file

        RTF control to demonstrate the following word processor related functions

-        Opening text, rtf

-        Saving text

-        Implementation of the page setup dialog control

-        Implementation of print preview dialog control

-        Searching text

-        Searching for and replacing text

-        Adding bullets to sections

-        Implementing undo/redo within an RTB

Implementing select all, cut, copy and paste in rtf control.

-        Embedding images

-        Setting page and font colors

-        Implement alignment options

We can create a rich text box control using a

Form designer at design time or using the rich text box class in code at run time.

Private sub Button1_click(Byval sender as System.object, Byval e as eventargs) handles Button1.click

rt as new richtextbox()

rt.location = new point(20,20)

rt.width =300

rt..height =200

rt.backcolor = Color.Red

rt.forcolor = Color.Blue

rt.text = “I am dynamic rich text box”

rt.font = new font(“Georgia”,16)

end sub

ShortcutsEnabled property applies to the following shortcut key combinations:

• CTRL+Z     Click the Undo command 
• CTRL+E      Aligns the line or selected text to the centre of the screen.
• CTRL+C     Copy selected text
• CTRL+Y     Redo the last action performed.
• CTRL+X    Cut selected text.
• CTRL+BACKSPACE   Deletes word to left of cursor.
•  
• CTRL+V                                 Paste.
• CTRL+DELETE                     Deletes word to right of cursor.
• CTRL+A                                  Select all contents of the page.

           

• CTRL+L                                    Aligns the line or selected text to the left of the screen.
• SHIFT+INSERT                        Paste.    

Menus

        The menu strip control represents the container for the menu structure. The menu strip control works as the top level container for the menu structure. The toolStripmenuItem class and the ToolStripDropdown menu class provide the functionalities to create menu items, sub menus and drop down menus.

        The context menu strip control represents a shortcut menu that popup over controls, usually when you right click them. They appear in context of some specific controls, so are called context menus. For example cut, copy or paste options properties.

        The toolstripmenuitem class supports the menus and menu items in a menu system. You handle these menu items through the click events in a menu system.

-hide and display menu items

-disable and enable menu items

-add access keys for menu items

-set short cut keys for menu items

 

Hide and display menu items

        The visible property of the toolstripmenuitem  class allows you to hide or show a menu item.

Private sub Button1_click(sender as object, e as EventArgs) handles Button1.click

Projectoolstripmenuitem1.visible=false

End sub

Disable and enable new items

        The Enabled property allows  you to disable or gray out a menu item.

Private sub Button1_click (sender as object, e as eventArgs) handles Button1.Click

projectToolstripmenuItem1.enabled =  false

end sub

        Access key

        Set access keys for a menu allows a user to select it from the keyboard by using the ALT key.

        If you want to set an access key Alt + F for the file menu, change its text with an added &(ampersand) preceding the access key.

        Short cut keys

        When you set a short cut key for a menu item, user can press the short cut from the keyboard and it would result in occurrence of the click event of the menu

        A short cut key is set for a menu item using the short cut keys property, To set a short cut key Ctrl + E for the edit menu 

                Menus are a part of every good application and provide not only an easy way to navigate within an application but also useful tools for working with that application. Take, for example, visual studio.net, it provides menus for navigating the various windows that it displays and useful tools for making the job of development easier through menus and context menus (also called pop-up menus). For cutting, copying and pasting code. It also provides menu items for searching through code.

        The main menu control in vb.net provides several key features. First and foremost is that it provides a quick and easy way to add menus, menu items and sub menu items in your applications.

        It also provides a built-in editor that allows you to add edit and delete menu items.

        An access key (als0 known as an accelerator key) allows you to navigate the menu using the Alt key and a letter that is underlined in the menu item. Once the access key has been used the menu will appear to the screen and the user can navigate through them using the arrow keys or the mouse.

        Short cut keys allow you to invoke the menu items without displaying the menus at all. For example, you usually, use a control key and a letter such as ctr + x to cut text.

    

Padding: how much space should appear between the content of an element

Righttoleft    no                      

Righttoleftautomirroring          false

          Automatic mirroring takes place when the original language of the form has a left to right

Shortcutkeys             none

Showshortcutkeys       true

Size                                   37,20

File handling

        File class is using for the file operations in vb.net. we can create, delete, copy, etc operations do with a File class.

File.create(“c:\testfile.txt”)

        Before we creating a file object, we usually check that file exists or not. For that, we are using the existing method in the File class.

        File.Exists(“c:\testfile.txt”)

        If we want the copy of the file object, we can use the copy method in File class.

        File.copy(“c:\textfile.txt”, “d:\testFile.txt”)

        When we want to delete a file object we can use the delete methods in the file class

        File.Delete(“c:\textfile.txt”)

        A file is a collection of data stored in a disk with a specific name and directory path. When a file is opened for reading or writing, it becomes a stream.

I/O classes

        The system.io namespace has various classes that are used for performing various operations with files, like creating and deleting files, reading from or writing to a file, closing file, etc,

I/O class                     Description

BinaryReader  reads primitive data

Binarywriter   writes primitive data

Directory      helps in manipulating a directory structure

Driveinfo     provides information for the drives

File                helps in manipulating files

StreamReader used for reading characters

StreamWriter     is used for writing characters

Imports system

Public class form1

Private sub Button1_click( byval sender as system.object, Byval e as Eventargs) handles Button1.click

If file.exists (“c:\textfile.txt”) then

   Msgbox(“file ‘textfile.txt’ exist”)

Else

   File.create(“c:\testfile.txt”)

   Msgbox(“file ‘textfile.txt’ created”)

End if

End sub

End class

The File Stream class represents a File in the computer. File stream allow to move data to and from the stream as arrays of bytes. We operate file using file mode in File Stream class.

Filemode.append : open and append to a file. If the file does not exist, it creates a new file.

Filemode.Create: Create a new file, if the file exist it will append to it.

Filemode.CreateNew: creates a new file. If the file exists, it throws exception

FileMode.open:   open an existing file

        Create a new directory, we can call createDirectory from directory class.

Directory.CreateDirectory(“c:\testdir”)

        Before we create a directory, we usually check that directory exist pr not. For that we are using the exists method in the directory class.

Directory.Exists (“c:\testdir”)

        If we want to move a directory and its contents from one location to another, we can use the move method in the directory class.

Directory.Move(“c:\testdir”, “c:\changedir”)

        When we want to delete a directory, we can use the delete method in the directory class.

        Directory.Delete (“c:\testdir”)

        IOException is the base class for exception thrown while accessing information using streams, files and directories. FileNotFoundException class is thrown the exception when an attempt to access a file that does not exist on disk fails.

Imports system.io

Class form1

Private sub Button1_click(byval sender as System.object, byval e as EventArgs) handles Button1.click

Try

File.copy(“c:\\tmp.txt”,”c:\\copytmp.txt”,true)

File.Delete (“c:\\copytmp.txt”)

Catch ex as System.IO.FileNotFoundException

Msgbox (ex.ToString())

End try

End sub

End class

File info class  

        It is providing properties and instance methods for the creation, copying, deletion, moving and opening of files.

        File info class is present int the I/O package. Whenever we call the file info class method need to import namespace like this

Imports System.IO

        Main properties of the class to get file information like file extension, last access time, filename etc

Creation time: creation time of the current file or directory

Extension: The extension part of the file

Isreadonly: if the current file is read-only

Last access time: time the current file or directory was last accessed.

Length: size in bytes, of the current file

Name: name of the file

File Stream class

        Exposes a stream around a file, supporting both synchronous and asynchronous read and write operations.

Position : set the current position of this stream

Read timeout: set a value, in milliseconds, that determines how long the stream will attempt to read before timing out.

Imports System.IO

Module Module1

Sub main()

Dim value As String = File.ReadAllText("C:\file.txt") Console.WriteLine(value.Length)

 End Sub

End Module

        In a sequential access file, you can write data to the file on reading from it sequentially from the beginning of the file to the end and vice versa.

        Random access file: In some situations, the programs require to access a particular record immediately. The records in random access files can without searching through a large number of records as in the case of a sequential access file. Random access file is used in instant access system such as banking system, sales system, airline reservation system

Dialog Box

        There are many built-in dialog boxes to be used in windows forms for various tasks like opening and saving files, providing a page, providing choices for colors, fonts, page setup etc, to the user of an application. These built-in dialog boxes reduce the developer’s time and work load.

Abort – when user clicks an abort button , to terminate

Retry - Attempt the operation again

Cancel - not save any of the changes made

Ignore – skip

      The color dialog control class represents a common dialog box that displays available colors along with controls that enable the user to define custom colors. It lets the user select a color.

Private sub button1_click (sender as object, e as EventArgs) handles button1.click

Label1.forecolor = ColorDialog1.Color

End sub

 

Font Dialog Control

      It prompts the user to choose a font from among these installed on the local computer and lets the user select the font, font size and color. It returns the Font and color objects.

Private sub Button2_click ( sender as object, e as EventArgs) handles button2.click

Richtextbox1.forecolor = FontDialog1.color

Richtextbox1.font = FontDialog1.Font

End sub

 

                Open File Dialog

        The open file dialog control prompts the user to open a file and allows the user to select a file to open. The user can check if the file exists and then open it.

properties                     Description

add extension           The dialog box automatically

                                    adds a extension to a file name if

                                     the user omits the extension

Check File exists       The dialog box displays a

                                    warning if the user specifies a file

                                    name that does not exists

private sub Button1_click (sender as object, e as EventArgs) handles Button1.click

PictureBox1.image = Image.FromFile (OpenFileDialog1.Filename)

end sub

        The OpenFileDialog component displays a dialog box that allow the user to choose a file to open

        The filename property can be set prior to showing the dialog box, to initally display the given file name.

class Form1

private sub Button1_click (Byval sender as System.Object, Byval e as System.EventArgs) handles Button1.click

dim dlg as new openfiledialog

dlg.showDialog()

dim filename as String

filename = dlg.FileName

msgbox(filename)

end sub

                Normally when you want your user to open a file in your application, you want to limit it to one or a couple of file types. For instance mostly opens word file (with the extension .doc or .docx) and notepad mostly open text files ( with the extension .txt)

Save File Dialog

        The save File Dialog control prompts the user to select a location for saving a file and allows the user to specify the name of the file to save data.

properties                  Description

DefaultExt        sets the default file name extension

Overwriteprompt   save as dialog box displays a

                                warning if the user specifies a file

                                name that already exists.

showhelp        The help button is displayed in the file

                         dialog box

title                  sets the file dialog box title

method         description

OpenFile     opens the file with read/write permission

private sub Button1_click ( sender as object, e as Eventargs) handles button1.click

saveFiledialog.Filter =( "text files ",*.txt)

end sub

autoupgradeEnabled :automatically upgrade appearance and behavior, control the behavior in certain events, assign hotkeys and shortcuts, add locations and use advanced service functions.

Check path exists : if path or directory does exists.

create prompt : whether the dialog box prompts the user for permission to create a file if the user specifies a file that does not exist.

  fault Ext :The extension that is used is determined by the Filter and DefaultExt properties

Dereferencelink : Whether the dialog box returns the location of the file referenced by the shortcut

filter index : If you set the FilterIndex property, that filter will be selected when the dialog box is displayed.

generate member:  List of all members, including inherited members.

initial directory:  represents the directory to be displayed when the open file dialog appears the first time.

SaveFileDialog.initialDirectory =@"d:\"

 

Various Controls available in Vb.net 

    Button control

        Windows forms controls are reusable components that encapsulate user interface functionality and are used in client-side windows applications. A button is a control which is an interactive component that enables user to communicate with an application which we click and release to perform some actions.

        The button control represents a standard button that reacts to a click event. A button can be clicked by using the mouse Enter key or space bar if the button has focus.

        Selects the form on which the button control resides.

In the properties window, set the form’s button properties to the button control’s name.

To respond to a button, click, in the button’s click event handler write the code to run button1_click must be bound to the control.

Forecolor, text properties of the button control are changed. Click event of the button is used to display a message.

        When you want to change display text of the button, you can change the text property of the button.

Button1.text = “My first button”

Similarly, if you want to load an image to a button control, you can code like this

Button1.image = Image.Fromfile(“ C:\mku.jpg”)

        The following vb.net source code shows how to change the button text property while form loading event and to display a message box button pressing a button control.

        Public class form1

        Private sub form1_load(byval sender as System.object, byval e as Eventargs) handles mybase.load

Button1.text=”click me”

End sub

Private sub button1_click(byval sender as System.object, byval e as System.Eventargs) handles Button1.click

Msgbox(http:\\www.mkuniversity.ac.in”)

End sub

End class

 Radio Button Control

                A radio button or option button is a type of GUI element that allows the user to choose only one of the predefined set of options. When a user clicks on a radio button, it becomes checked, and all other radio button with same group becomes unchecked.

        The radio button and the check box are used for different functions. Use a radio button when you want the user to choose only one option.

        The radio button control is used to provide a set of mutually exclusive options. The user can select one radio button in a group.

        Methods

Perform click

It is used to fire click event of radio button control

It is used to show radio button control

It is used to set cursor or focus on a radio button control.

Public class form1

Private sub radiobutton_checkedchanged (byval sender as system.object, Byval e as system.EventArgs) handles radiobutton1.checkedchanged, radiobutton2.checkedchanged, radiobutton3.checkedchanged

 If radionbutton1.checked = true then

Msgbox(“BCA”)

Elseif radiobutton2.checked = true then

    Msgbox (“B.Sc CS”)

Else

   Msgbox(“B.Sc IT”)

End if

End sub

End class 

Picture box control

        Picture box control is used to display images in bitmap, Gif, icon or jpeg formats.

        You can set the image property to the image you want to display, either at design time or at run time. You can programmatically change the image displayed in a picture box.

        Picturebox1.image = image.fromfile(“c:\mku.jpg”)

        The size mode property, which is set to values in the picture box size made enumeration, controls the clipping and positioning of the image in the display area.

Picturebox1.sizemode=picturebox.sizemode.stretchimage

          There are five different picture box size mode available to picture box control.

Auto size – sizes the picture box to the image

Center image -  centers the Image in the picture box

Normal – places the upper left corner of the image at

                  Upper left in the picture box.

Stretch image – allows you to stretch the image in code

        You can change the size of the display area at runtime with the client size property.

Picturebox1.clientsize = new size (x-size, y-size)

let us put a picture box and a button control on the form. We set the image property of the picture box to mku.jpg. The Click event of the button named Button1 is coded to stretch the image to a specified size

Timer Control

        Timer control plays an important role in the client side programming and server side programming, also used in windows services. By using this timer control, windows allow you to control when actions take place without the interaction of another thread.

        We can use timer control in many situations in our development environment. If you want to run some code after a certain interval of time continuously, you can use the timer, as well as to start a process at a fixed time schedule, to increase or decrease the speed in an animation graphics with time schedule etc

        With the timer control, we can control programs in milli second, seconds, minutes and even in hours. The timer control allows to set interval property in milliseconds ( 1 second is equal to 1000 milli seconds). For example, if we want to set an interval of two minute we set the value at interval property as 1 00 000, means 120 x 1000 .

        Public class form1

Private sub timer1_click( byval sender as System.object, byval e as System.EventArgs) handles timer1.tick

Lablel1.text = DateTime.Now.Tostring

End sub

End class

        Start and stop timer control we can control the timer control object that when it starts its function as well as when it stops its function. The timer control has a start and stop methods to perform these actions.

Timer1.start()       - timer starts functioning

Timer1.stop()       - timer stops functioning

Timer properties

Interval: gets or sets the interval at which to raise the elapsed event

Enabled: gets or sets a value indicating whether the timer should raise the elapsed event.

Name: A unique identifier for the control. This property is required and defaults to the name of the control.

The Modifiers property is the access modifier assigned to that member variable.

List box control

          Vb.net provides several mechanisms for gathering input in a program. List box control displays a list of choices which the user can select from.

          You can use the add or insert method to add items to a list box. The add method adds new items at the end of an unsorted list box. The insert method allows you to specify where to insert the item you are adding.

          Listbox1.items.add( “Sunday”)

          If you want to retrieve a single selected item to a variable, you can code like this

          Dim var as String

var   =listbox1.selectedItem

          If you change the selection mode property to multiple select, then you will retrieve a collection of items from listbox1.selecteditems property.

          Listbox1.selectionmode = selectionmode.multisingle

Private sub Button1_click (Byvalsender as System.object, Byva e as Eventargs) handles Button1.clivk

Listbox1.items.add(“Chennai”)

Listbox1.items.add(“bangalore”)

Listbox1.items.add(“hydrabad”)

Listbox1.items.add(“Trivandrum”)

End sub