Vb net xp_10

Performing File I/O Operations and Implementing
Multithreading in Visual Basic .NET
Objectives
In this lesson, you will learn to:
Identify the benefits of the .NET System.IO model
Identify the benefits of the Visual Basic .NET run-time
functions
Identify the benefits of multithreading
Implement threads in Visual Basic .NET

©NIIT Performing File I/O Operations and Implementing Multithreading in VB .NET/Lesson 10/
Slide 1 of 38

File
Is a collection of bytes that has a persistent storage.
I/O operations in Visual Basic .NET are handled in two
different ways:
Using the .NET System.IO model
Using the Visual Basic .NET run-time functions

Slide 2 of 38

System.IO Model
Specifies a set of classes that are available to all the .NET
languages.
Contains classes that are used for creating, copying,
moving, and deleting files.
Contains the following frequently used classes:
FileStream
BinaryReader and BinaryWriter
StreamReader and StreamWriter
Directory

Slide 3 of 38

The File Hierarchy in the System.IO Model

Slide 4 of 38

The FileStream Class
Provides access to files and file-related information.
Is used with the File class, which is contained in the
System.IO namespace, to create, copy, delete, move, and
open files.
Can also be used with another class called Path, to
manipulate the strings that represent folder or file paths.
Opens a file either in synchronous or asynchronous mode.
Opens files in synchronous mode by default.
Has constructors that use enumerations, such as FileMode,
FileAccess, and FileShare, to specify how a file is
created, opened, and shared.
Slide 5 of 38

FileMode Enumerations
Members Description

Append It is used to open a file if it exists and move
the file pointer to the end of the file, or
create a new file. Append can only be used
with the FileAccess.Write.

Create It is used to specify that the operating
system should create a new file. However,
if the file already exists, it will be
overwritten.

CreateNew It is used to specify that the operating
system should create a new file. However,
if the file already exists, it will throw an
exception.

Slide 6 of 38

FileMode Enumerations (Contd.)
Members Description

Open It is used to specify that the operating
system should open an existing file.

OpenOrCreate It is used to specify that the operating
system should open an existing file.
However, if the file does not exist, a new
file should be created.

Truncate It is used to specify that the operating
system should open an existing file. After
the file is opened, the file should be
truncated so that its size is zero bytes.

Slide 7 of 38

FileAccess Enumerations
Members Description

Read It is used to specify Read access to a file so
that data can be read from the file.

ReadWrite It is used to specify Read and Write access
to a file so that data can be written to and
read from the file.

Write It is used to specify Write access to a file so
that data can be written to the file.

Slide 8 of 38

FileShare Enumerations
Members Description

None It is used to decline sharing of the current
file. When this constant is used with the
FileShare enumeration, a request to open the
file will fail until the file is closed.
Read It is used to allow subsequent opening of a
file for reading. If this flag is not used, a
request to open the file for reading will fail
until the file is closed.
ReadWrite It is used to allow subsequent opening of a
file for reading or writing. If this flag is not
used, any request to open the file for writing
or reading will fail until the file is closed.

Write It is used to allow subsequent opening of a
file for writing. If this flag is not used, any
request to open the file for writing will fail
until the file is closed.

Slide 9 of 38

BinaryReader and BinaryWriter Classes
Are used to read from and write to a binary file.

StreamReader and StreamWriter Classes
Are used to read and write data as streams of
characters.
Use specific encoding to convert characters to and from
bytes.

Slide 10 of 38

The Directory Class
Enables you to work with drives and folders.
Method Usage

CreateDirectory() It is used to create the directories specified by
a path.

Delete() It is used to delete a directory and all its
contents.

Exists() It is used to determine whether the specified
path refers to an existing directory on the disk.

Slide 11 of 38

Directory Class (Contd.)

Method Usage

GetDirectoryRoot() It is used to return the root portion of a
specified path.

GetLogicalDrives() It is used to retrieve the names of the logical
drives on the current computer.

Move() It is used to move a directory and its contents
to a new path.

Slide 12 of 38

Just a Minute…
2. The code snippet generates a build error. Identify the error.
3. What is the difference between the CreateNew and Create
constants of the FileMode enumeration?
4. Complete the code to ensure that the file Product.txt is
opened with no share specification.

Slide 13 of 38

Visual Basic .NET Run-time Functions
Provide compatibility with earlier versions of Visual Basic.
Allow three types of file access:
Sequential
Random
Binary
Are defined in the System.IO.File namespace.

Slide 14 of 38

Functions Used to Access Files
Dir – It is used to retrieve the name of a file or directory that
matches a specific pattern based on the file attribute or
volume label of a file.
EOF – It is used to check whether the end of the file is
reached. When a file is opened for random or sequential
access, if the end of the file is reached, the function returns
a Boolean value True.
FileCopy – It is used to create a copy of an existing file.
FileDateTime – It is used to retrieve the date and time when
a file was created or last modified.
FileLen – It is used to retrieve the length of a file in bytes.

Slide 15 of 38

Functions Used to Access Files (Contd.)
FreeFile – It is used to retrieve the next file number
available for use by the FileOpen() function.
GetAttr – It is used to retrieve a FileAttribute value
representing the attributes of a file or directory.
Loc – It is used to retrieve a value specifying the current
read/write position within an open file.
LOF – It is used to retrieve a value representing the size, in
bytes, of a file opened using the FileOpen()function.
Seek – It is used to retrieve a value specifying the current
read/write position within a file opened using the
FileOpen()function or sets the position for the next
read/write operation within a file opened using the
FileOpen() function.
SetAttr – It sets the attribute information for a file.
Slide 16 of 38

Functions Used to Access Data from a File
With sequential access, a file can be opened in the Input,
Output, or Append mode. In the Input mode, a file is
opened for reading data from the file. In the Output or
Append mode, a file is opened for writing data to the
file. The syntax for using the FileOpen() function with
sequential access is as follows:
FileOpen(FileNumber, FileName,
OpenMode.mode type)

Slide 17 of 38

Functions Used to Access Data from a File (Contd.)
With random access, the FileOpen() function is used to
read and write data to a file without closing the file.
Random-access files store data in records, which makes it
easy to locate relevant information quickly. The syntax for
using the FileOpen() function with random access is as
follows:
OpenMode.Random,OpenAccess=OpenAccess.Default,
OpenShare=OpenShare.Default,RecordLength=
length of the record)

Slide 18 of 38

Functions Used to Access Data from a File (Contd.)
With binary access, the FileOpen() function is used to
read or write to any byte position in a file. The syntax
for using the FileOpen()function with binary access is
as follows:
OpenMode.Binary)

Slide 19 of 38

Functions Used to Write Data to and Read Data From
Files

Access type Functions for writing Functions for reading
data data

Sequential Print, PrintLine Input, InputString

Random FilePut FileGet

Binary FilePut FileGet

Slide 20 of 38

Just a Minute…
Complete the code to display the contents of the file named
Product.txt in the output window.

Slide 21 of 38

Problem Statement 10.D.1
The users at the call centers of Diaz Telecommunications
should be able to create a text file for storing customer
feedback on the services provided by Diaz
Telecommunications. The users should also be able to open
the file for future assessment.

Slide 22 of 38

Task List
Identify the mechanism to implement the user requirement.
Identify the controls needed to provide the user interface.
Perform the appropriate steps to design the form.
Write the code to implement the identified mechanism.
Save the application.
Run the application to validate the conditions applied on the
form.

Slide 23 of 38

Task 1: Identify the mechanism to implement the
user requirement.
Result:
You can fulfill the user requirement by using either the
classes in the System.IO model or the Visual Basic .NET
run-time functions. However, since the System.IO model is
a part of the .NET Framework class library, you should
implement the relevant classes of the System.IO model to
make full use of the .NET Framework features of Visual
Basic .NET.

Slide 24 of 38

Task 2: Identify the controls needed to provide the
user interface.
Result:
As per the plan, you need to add a RichTextBox control, a
label control, and two buttons, Read Data and Write
Data, to the form named frmCustomerFeedback.
In addition, a Reset button should be used to clear the
contents of the RichTextBox control.
To ensure that data is first written and then read from the
file, initially the Read Data button will be disabled. To
clear the contents of the RichTextBox, the Reset button will
be used.

Slide 25 of 38

Task 3: Perform the appropriate steps to design the
form.
Task 4: Write the code to implement the identified
mechanism.
Task 5: Save the application.
Task 6: Run the application to validate the conditions
applied on the form.

Slide 26 of 38

Problem Statement 10.P.1
The users at the call centers of Diaz Telecommunications
should be able to create a text file for storing product details
that are available for sale. The users should be able to read
from or write data to the file as a sequence of characters. The
users should also be able to open the file for future
assessment.

Slide 27 of 38

Threads
Help in performing multiple activities simultaneously.

MultiThreading
Is a process in which individual activities are executed on
separate threads.
Is also called free threading in Visual Basic .NET.
Enables you to create scalable applications since you can
add threads to an application as the workload increases.

Slide 28 of 38

Creating a Thread
Requires declaring a variable of the System.Threading.
Thread class and calling the constructor of the thread
class with the AddressOf operator and the name of the
procedure you want to execute on the new thread.
Example
Dim MyThread As New
System.Threading.Thread(AddressOf MySub)
Starting Execution of a Thread
You can start a thread by using the Start()method.
Stopping Execution of a Thread
You can stop the execution of a thread by calling the
Abort()method.
Slide 29 of 38

Thread Priorities
Are defined by using the Priority property.
By default set to Normal.
Can be changed by using the ThreadPriority
enumeration.
Values Description

AboveNormal Specifies that the thread has a higher
priority than Normal

BelowNormal Specifies that the thread has the lower
priority
Highest Specifies that the thread has the highest
priority
Lowest Specifies that the thread has the lowest
priority
Normal Specifies that the thread has an average
priority
Slide 30 of 38

Thread State
Is accessed by using the ThreadState property.
Can be a combination of the values in the
System.Threading.Threadstate enumeration, that is,
a thread can be in more than one state at a given time.
Can be changed by the following methods:
Thread.Sleep()
Thread.Suspend()
Thread.Interrupt()
Thread.Resume()
Thread.Abort()
Slide 31 of 38

Thread Lifecycle
Starts when an object of the System.Threading.Thread
class is created and stops when any of the following
occurs:
The method the thread is running completes
The process containing the thread terminates
The Abort() method is called for the thread object

Slide 32 of 38

Thread Lifecycle (Contd.)
The following diagram illustrates the thread states and the
methods that would cause the thread to leave each
state.

Slide 33 of 38

Multithreaded Procedures
Can accept arguments.
Can return values.

Thread Synchronization
Is done by using events in an application.
The SyncLock Statement
Ensures that multiple threads do not access shared data at
the same time.

Slide 34 of 38

Just a Minute…
There is a class called CalcClass, which has a Sub
procedure called CalculateArea(). You need to execute
this procedure in a separate thread. To execute the
CalculateArea() procedure, you need to declare a
variable of the thread type. Complete the declaration of the
variable in the code snippet.

Slide 35 of 38

Summary
In this lesson, you learned that:
The file I/O operations in Visual Basic .NET can be done in
two different ways:
Using the .NET System.IO model
Using the Visual Basic .NET run-time functions
The System.IO model specifies the use of the common
classes available to all the .NET languages.
The classes in the System.IO namespace that are mostly
used are:
FileStream
BinaryReader

Slide 36 of 38

Summary (Contd.)
BinaryWriter
StreamReader
StreamWriter
Directory
Visual Basic .NET run-time functions allow three types of file
access:
Sequential
Random
Binary
Threads can be implemented in Visual Basic by declaring a
variable of the System.Threading.Thread type.
Slide 37 of 38

Summary (Contd.)
The methods that are mostly used to manipulate a thread
are:
Start()
Sleep()
Suspend()
Resume()
Abort()

Slide 38 of 38

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