AhmedGamal-NET

Introduction to Prolog

2009-11-16T03:03:00.001+03:00

Prolog is a general purpose logic programming language associated with artificial intelligence and computational linguistics (Wikipedia Definition @ http://en.wikipedia.org/wiki/Prolog).

Prolog, LISP and many other languages depend on logic syntax and are represented as facts and rules. If you have any experience in programming using languages such as C#, JAVA or C++, then you need to change the way that you are using to write your codes.

How to start?

First of all, you need to download some tools to execute your commands; one of them is Amzi Development Environment. You can find it here: http://www.amzi.com/

What you have to do is just to open new file and write down your commands, then from Listener->Start you can start execute your code.

Code Syntax:

As we said in the beginning of this lesson, prolog depends on logical relationships, like:

Code Snippet
 Human(Ahmed)
Car(Toyota)
Human(Khaled)
 

This means that Ahmed and Khaled are humans. And Toyota is a car.

Let’s test those three lines; go to Listener -> Start then Listener -> Consult.

And in execution window, type the following question:

Code Snippet
 ?- Human(V).
 

Here we ask to show all humans and put it in array named V, you can press enter to quit or “;” to continue.

*** Note: (V) must be capital. All variables in Prolog must be capital.

The second type of questions is the Yes/No questions, like this:

Code Snippet
 ?- Human(Ahmed).
 

And you will get the answer depending on if you have added Ahmed to humans or not.

Relations:

In addition to previous, we can describe relationships between two items:

Code Snippet
 father(ahmed,mohammed)
father(ahmed,ali)
 

So if we ask the engine this question:

Code Snippet
 ?- father(ahmed,U)
 

We will have all Ahmed's sons in U list.

Rules:

That is the point where we will start get benefit from prolog, this is the way that human brain works when thinking. For example (all cars have a door and all planes also):

Code Snippet
 car(X) :- gotadoor(X).
airplane(X) :- gotadoor(X).
 

Then let's declare some planes and cars:

Code Snippet
 car(toyota)
car(mazda)
car(jagoar)
airplane(ai100)
 

If we ask if mazda have a door or not, prolog engine will be smart enough to answer with yes.

More about Prolog:

This is just simple introduction to Prolog. There are a lot of features in Prolog you can start with from this link:

http://kti.mff.cuni.cz/~bartak/prolog/learning.html

Example:

Einstein Problem, one of the famous puzzles. Where the puzzle author (Einstein or anybody else) said that 98% of peoples can’t solve this problem:

There are 5 houses sitting next to each other, each with a different color, occupied by 5 guys, each from a different country, and with a favorite drink, cigarette, and pet. Here are the facts:

The Brit lives in the red house

The Swede keeps dogs as pets.

The Dane drinks tea

The green house is on the left of the white house

The green house's owner drinks coffee

The person who smokes Pall Mall rears birds

The owner of the yellow house smokes Dunhill

The man living in the center house drinks milk

The Norwegian lives in the first house

The man who smokes Blends lives next to the one who keeps cats

The man who keeps horses lives next to the man who smokes Dunhill

The owner who smokes Bluemaster drinks beer

The German smokes Prince

The Norwegian lives next to the blue house

The man who smokes Blend has a neighbor who drinks water

The question is: Who owns the fish?

If we try to translate this problem into Prolog group of facts, rules and relationships, it will be like this:

Code Snippet
 next_to(X, Y, List) :- iright(X, Y, List).
next_to(X, Y, List) :- iright(Y, X, List).
iright(L, R, [L | [R | _]]).
iright(L, R, [_ | Rest]) :- iright(L, R, Rest).
einstein(Houses, Fish_Owner) :-
=(Houses, [[house, norwegian, _, _, _, _], _, [house, _, _, _, milk, _], _, _]),
member([house, brit, _, _, _, red], Houses),
member([house, swede, dog, _, _, _], Houses),
member([house, dane, _, _, tea, _], Houses),
iright([house, _, _, _, _, green], [house, _, _, _, _, white], Houses),
member([house, _, _, _, coffee, green], Houses),
member([house, _, bird, pallmall, _, _], Houses),
member([house, _, _, dunhill, _, yellow], Houses),
next_to([house, _, _, dunhill, _, _], [house, _, horse, _, _, _], Houses),
member([house, _, _, _, milk, _], Houses),
next_to([house, _, _, marlboro, _, _], [house, _, cat, _, _, _], Houses),
next_to([house, _, _, marlboro, _, _], [house, _, _, _, water, _], Houses),
member([house, _, _, winfield, beer, _], Houses),
member([house, german, _, rothmans, _, _], Houses),
next_to([house, norwegian, _, _, _, _], [house, _, _, _, _, blue], Houses),
member([house, Fish_Owner, fish, _, _, _], Houses).
 

Then if you ask prolog this question:

Code Snippet
 ?- einstein(Houses, Fish_Owner).
 

You will have the right solution, try to use your mind to solve it and correct it with Prolog solution, if your answer not German, so you are Candidate to join the 98% club. It is not so bad :)

Control Physical World Through Computer (Step by Step) - Part 3/3

2009-11-01T03:21:00.002+03:00

Second Example, Driving Remote Control Car

What we will need?

Remote Control Car.

Relay.

Transistor and Buffer (for security purpose only).

Some wires.

Start

Again we will use the same concept; we will use Relay to control the power from the remote control.

If we try to open and remote, we will find this structure:

If terminal (1) touches up terminal (2) it will go forward, (5) for left and so one.

That is what we can do using Relay. See this figure:

And that is all. Now, start implementing your application to close and open pins.

The only new thing is if you want to use keyboard keys, make keyPreview property of form to (True).

And write down this code in Form_KeyDown event:

if (e.KeyValue.ToString() == "37")

// left

else if (e.KeyValue.ToString() == "38")

// up

else if (e.KeyValue.ToString() == "39")

// right

else if (e.KeyValue.ToString() == "40")

// down

There are more complex remotes which allow you to control speed, break... etc.

But the general idea is the same.

More Applications

Introduction to Robots

In this part, we will try to explain simply what what the meaning of robot is. And how can we start implement small robot.

First of all, the robot is not only this kind of machine which is very similar to human body and face, the Robots is any machine with those 5 parts:

Body structure:

Muscle:

Sensor system:

Brain:

Power supply:

Start Work

Our simple robot mission is to detect the blue line on the ground and move on it.

We can use the same RC car that we have, we can use its body and motors as our body structure, muscles. And its battery as power supply.

Bring any webcam and put it in the front of the car, it will be our sensor system.

In our application, we will have simple Image Processing Code to read the video from webcam, read image by image from it, and detect the blue line, depends on that it will start drive right or left.

And that is our brain.

That was the simplest robot, it is good as beginning.

This is and advanced version, with microcontroller instead of connecting to computer, and motional camera:
http://www.youtube.com/watch?v=Shkur2WrWgA

Attached Files

The demo of this application is based in the application provided in this article:

http://www.codeproject.com/KB/cs/csppleds.aspx

But with more feature, you can open or close by the pin checkbox.

You can also run timer which provide different scenarios of opening/closing pins.

And if you have a seven segment, you can use it to count, it is contains seven segment equations.

And it is contains also the new inpout32.dll library.

Conclusion

Please if you find any mistake just inform me, and sorry for any mistake, I am not an electronic specialist.

Thanks. That it is all :)

This Article was provided before with Arabic Here

Control Physical World Through Computer (Step by Step) - Part 2/3

2009-11-01T02:55:00.002+03:00

4- Tools

To start dealing with hardware, it is better if you have some tools to help you, such as

Breadboard:

It will help you to put your wires and pins; it contains connected line (5 pins for example) with the same value so you can read it from many places.

Adapter

As we know, any digital device will need a VCC and Ground to work, any adapter will give you this, and it will be better if it comes with voltage controller (some devices needs more or less voltage).

Regulator

It is just to keep fixed voltage even if the voltage goes up, for example you can have 5V Regulator to give you 5V even if you use 9V battery.

Sample of Output Devices

Seven Segment: Represent Numbers using 8 LEDs.
Buzzer: Alarm instead of light in LED.
Screen: Advanced Screens using the same concept of seven segment.
Stepper Motors: Controlling Movement in the motor using digital signals.

Sample of Input Devices

KeyPad: Convert numbers or characters to binary digits.
Sensors: Fire Sensors, light sensors, water... etc which send custom signal when some physical event happen.

Sample of Controlling Devices

Buffer: Allow Signal to move whatever it is if the controller pin is equal to (One).
Relay: The same as buffer, but it can deal with 110/240V.
Microcontroller: Advanced Electronic Board, consists of multiple input, output and processing controls.

Relay and Controlling Electric Devices

By the end of this part, you must be able to control any electric device in your home. The general idea with any electric device is very simple, you have plugged cable to the power, if you cut the cable the device will switched off, if you reconnect it again it will work.

What we will try to do is just to put some controls, which will allow electricity to move or not depends on some value we will read it from computer. This Control as we said before can be Relay.

Example

There are many types of relay, each relay comes with its one datasheet, and we will choose one and explain using his datasheet.

In our relay we have 2 pins for controlling, and 3 pins in each side, when the control is (One) it will move the power from pin (1) to (3) in each side, else it will connect pin (1) to (2). This is how it will response:

There are some other types. This is one sample of it:

Now, back again to our work, we will use the relay instead of switch, and it will take the commands from pin2 form parallel port as VCC, and any ground (pin 25 as example):

Now try to run your application again, and enjoy. Just as a reminder again, open visual studio, import new inpout32.dll and write down this declaration:

using System.Runtime.InteropServices[DllImport("inpout32.dll", EntryPoint="Out32")]public static extern void Output(int adress, int value);

And to open the first data pin:

Output(888, 1);

For second pin type 2, third one is 4 and forth is 8 and so on. Now start implement any routine for that or for any electric device, open it through modem by calling, it is now just regular programming.

Security

In the previous example, we were connecting out electric circle directly to our parallel port, which is not safe. We must use some security circle in the middle. For example, we can use buffer gate between our parallel port and electric device in this way:

But we will face a problem that the output ampere from buffer will not be enough to deal with the relay, so we will add transistor to pass the power, and we will take outside VCC source to the relay:

Simplify

As we observed in the last security circle, we will have a lot of wires. And in real application, it will be very difficult to handle all of this in safe way. As a solution, electronic manufactories provide us something called (Parallel Port Interface).

This board consists of 8 relays with security circle, it will need only one General VCC and one Ground, and controls for each relay. It will work directly.

Algorithms

Sometime we will need to deal with more than 8 devices. For that purpose and other needs, we need to start reading about other gates. In this example, we will try to Control 8 devices using only 3 pins. for this purpose we will use Decoder. This is chart:

Control Physical World Through Computer (Step by Step) - Part 1/3

2009-11-01T02:31:00.003+03:00

Introduction

In this article, we will take the first step inside physical computing world.

Physical Computing, in the broadest sense, means building interactive physical systems by the use of software and hardware that can sense and respond to the analog world. In physical computing, we take the human body as a given, and attempt to design within the limits of its expression. (Wikipedia Definition)

Background

To be able to understand this article, those things must be clear for you:

1- Binary System

As we all know, the only understandable commands for any computer is the (On/Off) power commands which represented as 0 and 1.

And for those two commands, we have only three logical operators. They are (AND, OR and NOT).

And: 1 AND 1 is 1, anything else is equal to Zero.

OR: 0 OR 0 is 0, anything else is equal to One.

Not: Not 1 is Zero, Not 0 is One.

Those three operators are implemented using transistors so they will be able to deal with electricity and give the result.

After that, we have started implementing many functions using those three operators. And collecting them in some electric circles called gates, using those only we are able to build what we call as IC which can perform more complex operations to the data, and for storage also using the concept of flip flops.

You don't need to understand all of this, but at least you must understand the general points of how we can build computer using only (0 and 1).

2- Numerical System

As we said in previous section, we must represent our data using 0 and 1. We called it binary system.

So everything later must be converted to 0 and 1. Let us see how to represent our numbers (decimal number system), characters and symbols using this system.

For Example, this number (110101):

when we try to extract it to our decimal system, we can say it is:

(2^0*1)+(2^1*0)+(2^2*1)+(2^3*0)+(2^4*1)+(2^5*1) = 1+0+4+0+16+32=53.

For letters and symbols will find some encoding system such as ASCII which represent any single characters in 8 bit, for example it represent number (2) in this way (011 0010), (A) is (100 0001) and (/) is (010 1111).

3- Computer Ports

To start dealing with any external device, you must use one of computer ports to send your signals.

Here are examples of computer ports:

Serial Port

One of the oldest computer ports. It was used to connect external modem to the computer. It is sending 1 byte (8 bit) in each time.

USB Port

The most famous computer port. Most of new devices now are coming with USB port support.

With USB you can connect up to 127 device, you will have hot-swappable property so you will be able to have (Plug-in and Play). And with up to 480 MB/second speed in USB 2.0.

USB comes with only 4 wires, two for VCC/Ground, and the others for sending/receiving data.

Parallel Port

This is the port that we will use it in our examples, because it is the easiest one to deal with for the beginners.

You can find a very good article about it written by Levent Saltuklaroglu: http://www.codeproject.com/KB/cs/csppleds.aspx

Anyway, we will try to explain it one time again here.

Parallel port consists of 25 visible pens:

1, 14, 16 and 17: Control Pins, you can use them for both input and output.
2-9: Data Pins, you can use them to send data outside (output).
10-13 and 15: Status Pins, used for reading data (Input).
18-25: Ground Pins.

To start sending data through Parallel Port, you must have:

Kernel Mode Driver: such as inpout32.dll for windows users.

We will select C# as a programming language. You can select any.

Any device which we can show some data through, the simplest one is

LED

Now just take one LED, connect its positive pin to port number 2, and its negative one to any ground, and then open your visual studio any version, import inpout32.dll in this way:

[DllImport("inpout32.dll", EntryPoint="Out32")]

Then declare this function:

public static extern void Output(int adress, int value);

Finally, write some code like this in any button to open first pin:

Output(888, 1);

*** Hint: (888) is the Parallel Port Number, you can make sure from Device Manager->COM Ports->Parallel Port ->Resources-Resources Setting, may you will find it as hexadecimal, just convert it using your windows calculator.

*** Another Hint: Some time your inpout32.dll will gives you an error, use the one in the example.

StringBuilder

2009-10-31T20:14:00.007+03:00

Most of us when we concat any strings, we are using (+) operator (or & in vb.net) this way:

// C#
Label1.Text = Text1.Text + "@hotmail.com";
// Vb.net
Label1.Text = Text1.Text & "@hotmail.com"

But .net framework provides us another way to concat strings, using StringBuilder which is under System.Text name space, this is how to use:

//C#:
System.Text.StringBuilder mail = New System.Text.StringBuilder(Text1.Text);
mail.Append("@hotmail.com");
'VB.net:
Dim mail As New System.Text.StringBuilder(Text1.Text)
mail.Append("@hotmail.com")

What is the difference?

When using (+,&), new object will initialized every time we use this operator. But with StringBuilder, we will use the same object.

From Net Gotachas book, the auther(Venka) assume simple concat operations within loop. And he run the loop using different maximum values of loops. This is snap shoot from the book representing the execution time:

3562.933 second is equal to 59.4 minutes. So will you still use (+,&)?

Finaly, StringBuilder gives us another operations such as Replace, Insert and Remove, you can find all about it with a graphs represent the diferent from this article in CodeProject:
http://www.codeproject.com/KB/cs/StringBuilder_vs_String.aspx

Different Between Const and static readonly

2009-10-31T19:30:00.003+03:00

Declaring with const or static readonly will give the same result, we will have uneditable variable.

The only one difference is that (const) must take its value at compile time, but (static readonly) will take its value in run time.

so we can get more benefit from static readonly by declare it in static constructor:

class Program
{
public static readonly Test test = new Test();

static void Main(string[] args)
{
test.Name = "Program";
}

Introduction To WAP

2008-08-25T17:42:00.011+03:00

Introduction:
Through this topic we will work together to understand Technology of Wireless Application Protocol (WAP), also we will take a fast tour about developing WAP Applications using ASP.net.

Technology Description:

Mobile Application :
When First Mobile arrived, it was only smart way for sending and receiving voice calls and after sometime for sending and receiving text messages. But now, it is become the most growing market for services and recreational purposes. It is also being used for accessing internet and multimedia world.

For this reason, a lot of developing and programming concepts changed to become compatible with mobile world, one of these concepts was WAP as a mobile alternative of WEB concepts for regular computers.

What is WAP ؟

From Wikipedia, WAP is an open international standard for application layer network communications in a wireless communication environment. Its main use is to enable access to the Internet (HTTP) from a mobile phone or PDA.

How it Work ؟

The Biggest different between WAP and WEB is that WAP able to work through less capabilities and slow speed in comapre with the configuration of regular computers.

WAP starts since an order come from mobile customer, it is convert HTML page to WML pages that is able to browsing through mobiles.

What is WML ؟

It is description language very similar to HTML tags, it have only some few different:

- The main Tag is <wml> instead of <html>.

- Documents splits to <card></cards>.

Introduction To WML:

This is sample from Wiki about WML document:

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//PHONE.COM//DTD WML 1.1//EN"
"http://www.phone.com/dtd/wml11.dtd" >
<wml>
<card id="main" title="First Card">
<p mode="wrap">This is a sample WML page.</p>
</card>
</wml>

Reading and Writing Variables in WML:

Later you can display it like that:

<p>First Name: $(First_Name)</p>

You can also read textbox value with the same way:

<card id="card1" title="Tutorial">
<do type="accept" label="Answer">
<go href="#card2"/>
</do>
<p>
<select name="name">
<option value="HTML">HTML Tutorial</option>
<option value="XML">XML Tutorial</option>
<option value="WAP">WAP Tutorial</option>
</select>
</p>
</card>
<card id="card2" title="Answer">
<p>
You selected: $(name)
</p>
</card>
</wml>

ASP.net Application using WAP:

Do you remember our first WAP Application in this topic?

If you want to use it through ASP.net, you have to convert it to something like that:

<%@ Page Inherits="System.Mobile.UI.MobilePage" Language="C#" %>
<%@ Register TagPrefix="mobile" Namespace="System.Mobile.UI" %>
<mobile:Form runat="server">
<mobile:Label runat="server">
This is a sample WML page.
</mobile:Label>
</Mobile:Form>

If you want to work through VB.net instead of C#, just modify the first line like that:

<%@ Page Inherits="System.Mobile.UI.MobilePage" Language="C#" %>

And now, if your web site ordered from PC, the response will contain HTML tags, if it is ordered from Mobile, the response will contains WML tags.

Expression Blend

2008-08-24T01:32:00.003+03:00

When WPF - the new .net technology- arrived, Microsoft try to provide some tools makes life easy to WPF Developers, one of this tools was Expression Blend, we will try to show some features about it in this topic.

Try to download it form Microsoft web site, then run it and choose new Project - WPF Application (*.exe):

You can now choose your name, folder and .net language you want.

Click View-Active Document View then click split view to show both code and design view:

In the left side, you will find all tools you need for your design including painting tools such as brushs and pens. You can find also .net components such as commandbuttons. You can also click the link to more item to show all tools:

While you are painting, you will find additional properties for each tool in the right side:

Example:

Add new <canvas>, this will the container of our picture for this example:

Add new MediaElement to add a picture:

Now we will apply some effects through properties, this is an example of code results from some operations:

<Canvas.RenderTransform><TransformGroup>
<SkewTransform x:Name="MainSkewTransform" AngleY="-19" AngleX="0" CenterX="0" CenterY="0"/> <ScaleTransform x:Name="MainScaleTransform" ScaleY="1" ScaleX = "1" CenterX="0" CenterY="0"/></TransformGroup> </Canvas.RenderTransform></Canvas>

Press F5 now, this is a snap shot of expected results:

Now we will try to apply some shadow to the picture, so we will add <canvas> for a new picture object refer to the same file with new transformation parameters to make the second picture seems to be a shadow:

</MediaElement>

<Canvas.RenderTransform>

</TransformGroup>

</Canvas.RenderTransform>

</Canvas>

Previous Code Result:

Last topic in this lesson is to add some transparent to the shadow of picture through opacity property, the result XAML maybe like that:

</MediaElement>

<Canvas.RenderTransform>

</TransformGroup>

</Canvas.RenderTransform>

<Canvas.OpacityMask>

</LinearGradientBrush>

</Canvas.OpacityMask>

</Canvas>

Now, you have to try to edit the position of shadow by changing top and left manually, the result must be something like that:

Full XAML Code:

Don't forget that MediaElement can accept any type of media, try to attach video and see the result.

Anyway, you can copy this XAML code to a WPF .net solution and the same result will apply to your form.

IComparable Interface.

2008-06-17T22:02:00.005+03:00

From The name, this Interface used for comparison. This is the implementation of this interface:

C#:

public interface IComparable
{
int CompareTo(object o);
}

vb.net:

Public Interface IComparable
Function CompareTo(ByVal o As Object) As Integer
End Interface

The result of this function is Integer; it returns 0 in similarity, -1 when the first one is smaller and 1 when larger .

Now we don't need to know who is larger, let’s assume that we have car class, something like that:

C#:

class Car
{

string Name;
int year;
}

vb.net:

Class Car
Private Name As String
Private year As Integer
End Class

Now we need to sort the cars depends on the creation year, our first step it to implement IComparable interface.

C#:

class Car:IComparable
{

string Name;
int year;
}

vb.net:

class Car:IComparable
{

string Name;
int year;
}

Next, we should write an implementation to CompareTo function, something like that:

c#:

int IComparable.CompareTo(object obj)
{
Car temp = (Car)obj;
if(this.year > temp.year)
return 1;
if(this.year < temp.year)
return -1;
else
return 0;
}

vb.net:

Private Function CompareTo(ByVal obj As Object) As
Integer Implements IComparable.CompareTo
Dim temp As Car = DirectCast(obj, Car)
If Me.year > temp.year Then
Return 1
End If
If Me.year < temp.year Then
Return -1
Else
Return 0
End If
End Function

Anyway, -1 is equals to -100 in return value, this function work with any negative number referring to smaller, any positive number also is accepted instead of 1.

Sort Function:

Assume we have array of numbers, in this case some code like that is applicable.

c#:

Array.Sort(myNumbers);

vb.net:

Array.Sort(myNumbers)

But if we have array of cars, this will cause error, except if we implementing IComparable interface. in this case the array.sort() will use CompareTo function to sort all array elements. This is better solution than using another function for check and sorting. It is also more readable for people who work with you or read your code.

FileSystemWatcher

2008-06-05T15:16:00.004+03:00

FileSystemWatcher Class is very benefit when trying to monitor some files and inform user or program when any change occurs, all events are listed in NotifyFilters enum, this is the list of events can be handled by this:

public enum NotifyFilters {
Attributes, CreationTime, DirectoryName, FileName, LastAccess, LastWrite, Security, Size,
}

Now we need to declare functions to be called when some event occurred, this function will run through this delegate:

void MyNotificationHandler(object source, FileSystemEventArgs e)

Only rename event will run through this delegate:

void MyNotificationHandler(object source, RenamedEventArgs e)

Now we will start console application to monitor files, this application will run till user press q, this program will monitor all *.txt files in c:\ folder:

C#:

FileSystemWatcher watcher = new FileSystemWatcher();

// monitor files at:
watcher.Path = @"c:\";

// monitor files when
watcher.NotifyFilter = NotifyFilters.LastAccess NotifyFilters.LastWrite NotifyFilters.FileName NotifyFilters.DirectoryName;

// watch files of type
watcher.Filter = "*.txt";

// watch events:
watcher.Created += new FileSystemEventHandler(OnChanged);
watcher.Deleted += new FileSystemEventHandler(OnChanged);

watcher.EnableRaisingEventys = true;

Console.WriteLine("Press 'q' to quit app.");

while (Console.Read() != 'q') ;

vb.net:

Dim watcher As New FileSystemWatcher()

' monitor files at:
watcher.Path = "c:\"

' monitor files when
watcher.NotifyFilter = NotifyFilters.LastAccess Or NotifyFilters.LastWrite Or NotifyFilters.FileName Or NotifyFilters.DirectoryName

' watch files of type
watcher.Filter = "*.txt"

' watch events:
AddHandler watcher.Created, AddressOf OnChanged
AddHandler watcher.Deleted, AddressOf OnChanged

watcher.EnableRaisingEvents = True

Console.WriteLine("Press 'q' to quit app.")

While Console.Read() <> "q"C

End While

As you seen, we call OnChanged function every event occurs, so we can implement this function to print this event and its time like that:

C#:

static void OnChanged(object source, FileSystemEventArgs e)

{

Console.WriteLine("File Changed, File Path: {0} , Change: {1}, DateTime: {2}", e.FullPath, e.ChangeType,DateTime.Now.ToString());

}

vb.net:

Private Shared Sub OnChanged(ByVal source As Object, ByVal e As FileSystemEventArgs)

Console.WriteLine("File Changed, File Path: {0} , Change: {1}, DateTime: {2}", e.FullPath, e.ChangeType, DateTime.Now.ToString())

End Sub

Now, this is screen shot of application when delete .txt file and create it again.

Introduction to AJAX in .net Applications

2007-09-14T02:29:00.004+03:00

In the name of Allah.

Introduction to AJAX in .net Applications

Fast tour in Microsoft Ajax Toolkit

In this lesson we will take a fast tour in Microsoft Ajax world. First we have to know what the meaning of AJAX is.

AJAX or Asynchronous JavaScript and XML is a term describing a web development technique for creating interactive web applications using a combination of: HTML (or XHTML) and Cascading Style Sheets (CSS) for presenting information* Document Object Model, JavaScript to dynamically display and interact with the information presented* XML, XSLT and the XMLHttpRequest object to interchange and manipulate data asynchronously with the web server (although AJAX applications can use other technologies.

*** Wikipedia definition for AJAX at link:
http://en.wikipedia.org/wiki/AJAX

Anyway it is a type of programming made popular with since 2005 by Google. It is not a new programming language but it is depends on good connection and using of existing resources to establish an interactive web-based application. Basically, it depends on divide web page into separate parts all of them can be re- loaded alone without interference with other parts.

One of the most famous Ajax-enabled web application is Google service. Also new mail service from yahoo and hotmail also supported with Ajax concepts.

How can I start working with Ajax through asp.net?

Microsoft publishes Microsoft Ajax Toolkit to provide a simple tool can be used to benefit from Ajax technology; you can start by downloading tools through this link: http://www.asp.net/ajax/

Or you can trace large amount of controls live through this link:
http://www.asp.net/ajax/control-%20toolkit/live/

If you search for some useful tutorials about asp.net in general you can visit this link:
http://www.asp.net/learn/default.aspx?tabid=63

And especially with Ajax you can find video tutorials here:
http://www.asp.net/learn/ajax-videos/

you can have a fast start with Ajax using this video:
http://www.asp.net/learn/ajax-%20videos/video-75.aspx

And this video for Microsoft Ajax Tools:
http://www.asp.net/learn/ajax-%20videos/video-76.aspx

Finally, you can still build your own Ajax work from scratch using HTML (or XHTML) with JavaScript or by using old Microsoft technology (Atlas) which support partial processing for WebPages, you can find more about Atlas in this video:
http://download.microsoft.com/download%20/0/f/6/0f651a0f-6f2b-4497-b061-%20e1b2825e22e0/MSAJAX-ToDoList-Video.zip

This article written by Arabic in:
http://www.vb4arab.com/vb/showthread.php?t=15

Thanks.