Help understanding delegates?

[Brett]

I'd like to better understand how the following code works. I've posted
questions below.

namespace Something.Somet hing1
{
using System;

public delegate void Test1();
public delegate void Test2(ink k);

public class A
{
public static void Log1 (int l)
{
Console.WriteLi ne(":{0}",l);
}

public void Log2 (int l)
{
Console.WriteLi ne("#{0}",l);
}
}

public class Class1
{
public static void Main()
{
A a = new A();
Test2 t0 = new Test2(A.Log1); //use static method
Test2 t1 = new Test2(a.Log2); //use instance method

t0 += t1; t0(0);
t0 -= t1; t0(1);
}
}
}

This will print ":0 #0 :1". How does Log1 print 0 when no param is passed
to it and "l" is not initialized to 0?

What are the differences in the static and instance method calls via
delegates?

This line t0 -= t1; t0(1); removes those methods from the delegate
collection correct? How is the output affected if that line does not
exists?

Also, if I'm using the IE object and have three successive page loads, will
each of the following events respectively fire after each page load rather
than all three always firing after each page load? In other words, after
the first page load completes, onIEDocComplete 1 fires. After the second
page load completes, onIEDocComplete 2 fires. After the third page load
completes, onIEDocComplete 3 fires.

IE_Inst.Documen tComplete += new
SHDocVw.DWebBro wserEvents2_Doc umentCompleteEv entHandler(this .onIEDocComplet e1);

IE_Inst.Documen tComplete += new
SHDocVw.DWebBro wserEvents2_Doc umentCompleteEv entHandler(this .onIEDocComplet e2);

IE_Inst.Documen tComplete += new
SHDocVw.DWebBro wserEvents2_Doc umentCompleteEv entHandler(this .onIEDocComplet e3);

Thanks,
Brett

[Mattias Sjögren]

How does Log1 print 0 when no param is passed
to it and "l" is not initialized to 0?
What do you mean no param is passed to it? You're passing 0 when
invoking the delegate so that's the value l will get.

What are the differences in the static and instance method calls via
delegates?
No differences apart from the ones seen in regular method calls.

This line t0 -= t1; t0(1); removes those methods from the delegate
collection correct?
It removes the t1 methods (Log2) from t0, but leaves Log1.

How is the output affected if that line does not exists?

Why don't you try it and see.

Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Brett]

"Mattias Sjögren" <ma************ ********@mvps.o rg> wrote in message
news:uf******** ******@TK2MSFTN GP14.phx.gbl...

How does Log1 print 0 when no param is passed
to it and "l" is not initialized to 0?

What do you mean no param is passed to it? You're passing 0 when
invoking the delegate so that's the value l will get.

I mean to say t1 or Log2. Zero is not passed it yet it is displayed.

Any suggestions on the IE question?

[Mattias Sjögren]

>>>How does Log1 print 0 when no param is passed

to it and "l" is not initialized to 0?
What do you mean no param is passed to it? You're passing 0 when
invoking the delegate so that's the value l will get.

I mean to say t1 or Log2. Zero is not passed it yet it is displayed.

Log2 is called with the argument 0 when you invoke the t0 delegate
because Log2 is in t0's list of methods to call after you do t0 += t1.

Any suggestions on the IE question?

Also, if I'm using the IE object and have three successive page loads, will
each of the following events respectively fire after each page load rather
than all three always firing after each page load?

No they will all fire for every load event. If that's not what you
want, you'll have to remove the onIEDocComplete 1 handler and add the
onIEDocComplete 2 one when onIEDocComplete 1 is called.

Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Brett]

"Mattias Sjögren" <ma************ ********@mvps.o rg> wrote in message
news:OQ******** ******@TK2MSFTN GP14.phx.gbl...

How does Log1 print 0 when no param is passed
to it and "l" is not initialized to 0?

What do you mean no param is passed to it? You're passing 0 when
invoking the delegate so that's the value l will get.

I mean to say t1 or Log2. Zero is not passed it yet it is displayed.

Log2 is called with the argument 0 when you invoke the t0 delegate
because Log2 is in t0's list of methods to call after you do t0 += t1.

Any suggestions on the IE question?

Also, if I'm using the IE object and have three successive page loads,
will
each of the following events respectively fire after each page load
rather
than all three always firing after each page load?

No they will all fire for every load event. If that's not what you
want, you'll have to remove the onIEDocComplete 1 handler and add the
onIEDocComplete 2 one when onIEDocComplete 1 is called.

So is a delegate basically a collection of method pointers that when called,
executes all methods in the collection in the order they were added to the
collection?

Brett

[Brett]

"Mattias Sjögren" <ma************ ********@mvps.o rg> wrote in message
news:OQ******** ******@TK2MSFTN GP14.phx.gbl...

How does Log1 print 0 when no param is passed
to it and "l" is not initialized to 0?

What do you mean no param is passed to it? You're passing 0 when
invoking the delegate so that's the value l will get.

I mean to say t1 or Log2. Zero is not passed it yet it is displayed.

Log2 is called with the argument 0 when you invoke the t0 delegate
because Log2 is in t0's list of methods to call after you do t0 += t1.

Any suggestions on the IE question?

Also, if I'm using the IE object and have three successive page loads,
will
each of the following events respectively fire after each page load
rather
than all three always firing after each page load?

No they will all fire for every load event. If that's not what you
want, you'll have to remove the onIEDocComplete 1 handler and add the
onIEDocComplete 2 one when onIEDocComplete 1 is called.

Mattias

How exactly do I remove the IE delegate?

I try:

IE_Inst.Documen tComplete -=
SHDocVw.DWebBro wserEvents2_Doc umentCompleteEv entHandler(this .onIEDocComplet e);

Compiler says:
Method 'appname.IE.onI EDocComplete(ob ject, ref object)' referenced without
parentheses

So I try
IE_Inst.Documen tComplete -=
SHDocVw.DWebBro wserEvents2_Doc umentCompleteEv entHandler(this .onIEDocComplet e());

Compiler says:
No overload for method 'onIEDocComplet e' takes '0' arguments

Brett

[Mattias Sjögren]

So is a delegate basically a collection of method pointers that when called,
executes all methods in the collection in the order they were added to the
collection?
Correct, except that I believe the order they are called in is
undefined and implementation dependent.

How exactly do I remove the IE delegate?

I try:

IE_Inst.Docume ntComplete -=
SHDocVw.DWebBr owserEvents2_Do cumentCompleteE ventHandler(thi s.onIEDocComple te);

Compiler says:
Method 'appname.IE.onI EDocComplete(ob ject, ref object)' referenced without
parentheses

Insert the new keyword before the event type.

IE_Inst.Documen tComplete -= new
SHDocVw.DWebBro wserEvents2_Doc umentCompleteEv entHandler(this .onIEDocComplet e);

Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Jon Skeet [C# MVP]]

Mattias Sjögren <ma************ ********@mvps.o rg> wrote:

So is a delegate basically a collection of method pointers that when called,
executes all methods in the collection in the order they were added to the
collection?

Correct, except that I believe the order they are called in is
undefined and implementation dependent.

Nope - the order is guaranteed. Have a look at the docs for
Delegate.Combin e for a few more details.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Jon Skeet [C# MVP]]

Jon Skeet [C# MVP] <sk***@pobox.co m> wrote:

Correct, except that I believe the order they are called in is
undefined and implementation dependent.

Nope - the order is guaranteed. Have a look at the docs for
Delegate.Combin e for a few more details.

Sorry, looking further, I can't see anything that absolutely guarantees
that when you call Invoke, the delegates are executed in the
appropriate order. However, things like the C# specification assume
that that's going to happen, and I think it's a pretty reasonable
assumption to make.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Willy Denoyette [MVP]]

"Brett" <[e-mail]> wrote in message
news:%2******** ********@TK2MSF TNGP10.phx.gbl. ..

"Mattias Sjögren" <ma************ ********@mvps.o rg> wrote in message
news:OQ******** ******@TK2MSFTN GP14.phx.gbl...

>How does Log1 print 0 when no param is passed
>to it and "l" is not initialized to 0?

What do you mean no param is passed to it? You're passing 0 when
invoking the delegate so that's the value l will get.

I mean to say t1 or Log2. Zero is not passed it yet it is displayed.

Log2 is called with the argument 0 when you invoke the t0 delegate
because Log2 is in t0's list of methods to call after you do t0 += t1.

Any suggestions on the IE question?

Also, if I'm using the IE object and have three successive page loads,
will
each of the following events respectively fire after each page load
rather
than all three always firing after each page load?

No they will all fire for every load event. If that's not what you
want, you'll have to remove the onIEDocComplete 1 handler and add the
onIEDocComplete 2 one when onIEDocComplete 1 is called.

Mattias

How exactly do I remove the IE delegate?

I try:

IE_Inst.Documen tComplete -=
SHDocVw.DWebBro wserEvents2_Doc umentCompleteEv entHandler(this .onIEDocComplet e);

You are missing the "new"

IE_Inst.Documen tComplete -= new ....

Not sure why you don't take some time to read the Events tutorial in MSDN's
"C# Programmers Reference"

Willy.