Delegation

[Abalfazl]

Hello

http://www.csharp-station.com/Tutorials/Lesson14.aspx




using System;
using System.Drawing;
using System.Windows.forms;

// custom delegate
public delegate void Startdelegate();

class Eventdemo : form
{
// custom event
public event Startdelegate StartEvent;

public Eventdemo()
{
Button clickMe = new Button();

clickMe.Parent = this;
clickMe.Text = "Click Me";
clickMe.Location = new Point(
(ClientSize.Width - clickMe.Width) /2,
(ClientSize.Height - clickMe.Height)/2);

// an EventHandler delegate is assigned
// to the button's Click event
clickMe.Click += new EventHandler(OnClickMeClicked);

// our custom "Startdelegate" delegate is assigned
// to our custom "StartEvent" event.
StartEvent += new Startdelegate(OnStartEvent);

// fire our custom event
StartEvent();
}

// this method is called when the "clickMe" button is pressed
public void OnClickMeClicked(object sender, EventArgs ea)
{
MessageBox.Show("You Clicked My Button!");
}

// this method is called when the "StartEvent" Event is fired
public void OnStartEvent()
{
MessageBox.Show("I Just Started!");
}

static void Main(string[] args)
{
Application.Run(new Eventdemo());
}
}




And this from :http://www.codeguru.com/csharp/csharp/cs_delegates/eventhandling/






using System;
//Step 1 Create delegate object
public delegate void MyHandler1(object sender,MyEventArgs e);
public delegate void MyHandler2(object sender,MyEventArgs e);

//Step 2 Create event handler methods
class A{
public const string m_id="Class A";
public void OnHandler1(object sender,MyEventArgs e){
Console.WriteLine("I am in OnHandler1 and MyEventArgs is {0}",
e.m_id);
}
public void OnHandler2(object sender,MyEventArgs e){
Console.WriteLine("I am in OnHandler2 and MyEventArgs is {0}",
e.m_id);
}

//Step 3 create delegates, plug in the handler and register
// with the object that will fire the events
public A(B b){
MyHandler1 d1=new MyHandler1(OnHandler1);
MyHandler2 d2=new MyHandler2(OnHandler2);
b.Event1 +=d1;
b.Event2 +=d2;
}
}

//Step 4 Calls the encapsulated methods through the
// delegates (fires events)
class B{
public event MyHandler1 Event1;
public event MyHandler2 Event2;
public void FireEvent1(MyEventArgs e){
if(Event1 != null){
Event1(this,e);
}
}
public void FireEvent2(MyEventArgs e){
if(Event2 != null){
Event2(this,e);
}
}
}
public class MyEventArgs EventArgs{
public string m_id;
}
public class Driver{
public static void Main(){
B b= new B();
A a= new A(b);
MyEventArgs e1=new MyEventArgs();
MyEventArgs e2=new MyEventArgs();
e1.m_id ="Event args for event 1";
e2.m_id ="Event args for event 2";
b.FireEvent1(e1);
b.FireEvent2(e2);
}
}





I have 2 questions,

In first example ,It didn't used



But in second example,It is used
Why?

When do we use EventArgs?

[Abalfazl]

Hello


From Programming C#, 4th Edition




namespace EventKeyword
{

// a class to hold the information about the event
// in this case it will hold only information
// available in the clock class, but could hold
// additional state information
public class TimeInfoEventArgs : EventArgs
{
public readonly int hour;
public readonly int minute;
public readonly int second;
public TimeInfoEventArgs(int hour, int minute, int second)
{
this.hour = hour;
this.minute = minute;
this.second = second;
}
}

// our subject -- it is this class that other classes
// will observe. This class publishes one event:
// OnSecondChange. The observers subscribe to that event
public class Clock
{
private int hour;
private int minute;
private int second;

// the delegate the subscribers must implement
public delegate void SecondChangeHandler
(
object clock,
TimeInfoEventArgs timeInformation
);

// the keyword event controls access to the delegate
public event SecondChangeHandler OnSecondChange;

// set the clock running
// it will raise an event for each new second
public void Run( )
{

for(;;)
{
// sleep 10 milliseconds
Thread.Sleep(10);

// get the current time
System.DateTime dt = System.DateTime.Now;

// if the second has changed
// notify the subscribers
if (dt.Second != second)
{
// create the TimeInfoEventArgs object
// to pass to the subscriber
TimeInfoEventArgs timeInformation =
new TimeInfoEventArgs(
dt.Hour,dt.Minute,dt.Second);

// if anyone has subscribed, notify them
if (OnSecondChange != null)
{
OnSecondChange(
this,timeInformation);
}
}

// update the state
this.second = dt.Second;
this.minute = dt.Minute;
this.hour = dt.Hour;
}
}
}

// an observer. DisplayClock subscribes to the
// clock's events. The job of DisplayClock is
// to display the current time
public class DisplayClock
{
// given a clock, subscribe to
// its SecondChangeHandler event
public void Subscribe(Clock theClock)
{
theClock.OnSecondChange +=
new Clock.SecondChangeHandler(TimeHasChanged);
}

// the method that implements the
// delegated functionality
public void TimeHasChanged(
object theClock, TimeInfoEventArgs ti)
{
Console.WriteLine("Current Time: {0}:{1}:{2}",
ti.hour.ToString( ),
ti.minute.ToString( ),
ti.second.ToString( ));
}
}

// a second subscriber whose job is to write to a file
public class LogCurrentTime
{
public void Subscribe(Clock theClock)
{
theClock.OnSecondChange +=
new Clock.SecondChangeHandler(WriteLogEntry);
}

// This method should write to a file.
// We write to the console to see the effect.
// This object keeps no state.
public void WriteLogEntry(
object theClock, TimeInfoEventArgs ti)
{
Console.WriteLine("Logging to file: {0}:{1}:{2}",
ti.hour.ToString( ),
ti.minute.ToString( ),
ti.second.ToString( ));
}
}

public class Test
{
public static void Main( )
{
// create a new clock
Clock theClock = new Clock( );

// create the display and tell it to
// subscribe to the clock just created
DisplayClock dc = new DisplayClock( );
dc.Subscribe( theClock );

// create a Log object and tell it
// to subscribe to the clock
LogCurrentTime lct = new LogCurrentTime( );
lct.Subscribe( theClock );

// Get the clock started
theClock.Run( );
}
}
}




May someone explain about this part of code:



if (OnSecondChange != null)
{
OnSecondChange(
this,timeInformation);
}
}




I don't know but I think,But I think it should be something like this:

Onsecondchange =+new secondchangehandler(funcname)...

[Abalfazl]

Hello

about this:



public void OnHandler1(object sender,MyEventArgs e)



May someone explain it?

http://www.codeguru.com/csharp/csharp/cs_delegates/eventhandling/