Re: Event,Delegation - C# Discussion Boards

25-Mar-07 7:26

Hello

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

[code]

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());
}
}
[/code]

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

[code]

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);
}
}

[/code]

I have 2 questions,

In first example ,It didn't used

But in second example,It is used
Why?

When do we use EventArgs?

abalfazl25-Mar-07 7:27

25-Mar-07 7:27

Hello

From Programming C#, 4th Edition

[code]

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( );
}
}
}

[/code]

May someone explain about this part of code:

[code]

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

[/code]

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

Onsecondchange =+new secondchangehandler(funcname)...

abalfazl25-Mar-07 20:43

25-Mar-07 20:43

Anyone knows the answer?

abalfazl25-Mar-07 7:28

25-Mar-07 7:28

Hello

about this:

[code]

public void OnHandler1(object sender,MyEventArgs e)

[/code]

May someone explain it?

[url]http://www.codeguru.com/csharp/csharp/cs_delegates/eventhandling/[/url]

Self Updating Application #$%@

Mike Hankey25-Mar-07 7:47

Mike Hankey

25-Mar-07 7:47

Custom EventArgs are used when you need to pass additional information to the subscriber.

You don't use custom event args in cases where you just want to know something happened such as a button click. You know its a button and its been clicked.
You use custom event args if you want more info about the event say if you want to know the background color of the button.

public class MyEventArgs : EventArgs
{
public Color btnColor;

public MyEventArgs(Color color)
{
btnColor = color;
}
}

then when you create;
if (myHandler != null)
myHandler(this, new MyEventArgs(button1.BackColor);

Hope this helps
Mike

Everybody gotta be somebody

Steve Messer25-Mar-07 7:11

25-Mar-07 7:11

I am trying to create a self updating application. I am sure that you have heard of .Net Reflector.

It is a single exe which has the ability to update it self. Oddly enough it you try to use Reflector on itself it has be ofuscated. So, I can't see what he has done.

Here is how it works.

1. You start up the app and it detects that it needs an update.
2. It appears to shut itself down, download the updated exe and then restarts it.

It you watch the process list you will see that during the update process he spawns (starts...)
a process called tmp6E.exe, which I am guessing does the work.

I have coded up a solution but it doesn't work correctly.

1. I embedded an update.exe program in my main app which does the updating, which works fine.
2. I have tried not using it embedded but I still have the same problem.

How do you start/spawn a process and then shut down the parent (calling app) so that you can
over write it?

Christian Graus25-Mar-07 9:21

Christian Graus

25-Mar-07 9:21

Probably with Process.Start, I'd imagine a call to Procss.Start followed by this.Close() would not close the spawned process.

Steve Messer25-Mar-07 10:41

25-Mar-07 10:41

That's what I tried first. But it doesn't work.

static void Main()
{
   Application.EnableVisualStyles();
   Application.SetCompatibleTextRenderingDefault(false);
   Application.Run(new Form1());  <<<---- exception here.
}

I get the following exception
{"Cannot access a disposed object.\r\nObject name: 'Form1'."}

Christian Graus25-Mar-07 12:40

Christian Graus

25-Mar-07 12:40

When do you get this exception ? What do you do to restart Main, or do you just get it when you run the app the second time ? If so, how do you run it ?

Steve Messer25-Mar-07 13:00

25-Mar-07 13:00

Okay, I found part of my problem. First let me explain what I am trying to do.

I currently have two exe's.

1. MainApp.exe (has two forms the main form and an update form)
2. Update.exe

When MainApp.exe starts up it downloads a file from one of my web pages (version.txt)
it currently contains 2.0.0.0. I then compare my current version which is 1.0.0.0 and
if the version on the server is larger than my current version I create an instance
of my update form which says "There is an update available do you want to automatically
update?". If you click no I just close the update form and then the main form is shown.
If you click yes, I close the update form and I start the update.exe as a process.
Then I want to exit out of the MainApp.exe and let update.exe download the update
replacing the current out of date one.

My first problem is that I was doing this logic inside the MainForm constructor. If you
attempt to call this.Close() the form has even finished creating itself and thus my problem.

My next problem seems that I am in a continuous loop calling my update form in the MainApp over
and over again.

Patrick Etc.25-Mar-07 12:52

Patrick Etc.

25-Mar-07 12:52

The easiest thing to do would be to load your assembly (assemblies) in a shadow cache - this is a little known feature of .NET that copies your assemblies to a temporary directory before executing them. This is done explicitly for the purpose you are asking - software updates - but also for some other, very obscure security reasons that I don't fully understand myself.

At any rate, I first learned of the approach from the Morrison Schartz plugin manager, so you might download their plugin source code and take a look. There are also several articles here on Code Project that use a strikingly similar approach, so they would be good to look at (search for "application auto-update").

For the Morrison Schwartz approach, go here: http://www.ms-inc.net/dotnet.aspx?ProductID=Plugins

Steve Messer25-Mar-07 13:01

25-Mar-07 13:01

Interesting, thanks I will look into your suggestions.

Steve Messer29-Mar-07 5:00