Asynchronous Delegate w/ Callback Parameters

Michael C · Sep 13, 2004

Hi all,

Is there an easy way to get the parameters of an asynchronous delegate call
from the callback function? Here's an example of what I'm trying to do:

private delegate ArrayList AsyncDelegate (string server);

private void GetServerInfo (string server)
{
AsyncDelegate ad = new AsyncDelegate(GetServerArray);
IAsyncResult iar = ad.BeginInvoke(server, new
AsyncCallback(EndGetServerInfo), ad);
}

private void EndGetServerInfo(IAsyncResult iar)
{
AsyncDelegate ad = (AsyncDelegate)iar.AsyncState;
ArrayList a = ad.EndInvoke(iar);
}

private ArrayList GetServerArray(string server)
{
ArrayList a = new ArrayList();
// this code establishes a SQL connection, executes a
// few queries and .Adds the results to the ArrayList
return (a);
}

In this code, GetServerInfo executes the "GetServerArray" routine
asynchronously. This routine basically connects to a SQL Server, executes a
couple of SELECT statements and returns the results in an ArrayList. After
completion, the EndGetServerInfo is called, and I retrieve the results via
..EndInvoke.

Everything works great, and I get my ArrayList of information, but there's
one small problem: in the EndGetServerInfo callback routine, I need to
retrieve not just the returned ArrayList, but also the initial parameter I
passed into the "GetServerInfo" routine (i.e., the "string server"
variable).

I imagine there's an easy way to do this via the IAsyncResult, but I'm not
sure how. Any ideas? Or would it be easier just to have my
"GetServerArray" routine .Add the value of the "server" variable as the
first item on the returned ArrayList? Seems kind of hokey, and would like
to avoid that if possible.

Thanks,
Michael C., MCDBA

Richard Blewett [DevelopMentor] · Sep 13, 2004

There is no automatic way to do this AFAIK but there is a mechanism available.

ad.BeginInvoke(server, new AsyncCallback(EndGetServerInfo), ad);

This last parameter is the AsyncState - you can pass anything in here so pack up your parameters in an object and pass it this way. Now the issue is "how do I get the delegate instance to call EndInvoke?"

Well it is documented (and therefore you can rely on it) that the IAsyncResult you get in a AsyncCallback is actually an AsyncResult instance. This class is in the System.Runtime.Remoting.Messaging namespace (where else ;-) ). So you can write your callback as follows:

Void Callback( IAsyncResult iar )
{
AsyncResult ar = (AsyncResult)iar;

AsyncDelegate mydel = (AsyncDelegate)ar.AsyncDelegate; // AsyncDelegate is a property on the AsyncResult

MyParamsObject mp = (MyParamObject)ar.AsyncState;

...
}

HTH

Regards

Richard Blewett - DevelopMentor
http://staff.develop.com/richardb/weblog
?
nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/
Hi all,

Is there an easy way to get the parameters of an asynchronous delegate call from the callback function? Here's an example of what I'm trying to do:

private delegate ArrayList AsyncDelegate (string server);

private void GetServerInfo (string server) { AsyncDelegate ad = new AsyncDelegate(GetServerArray); IAsyncResult iar = ad.BeginInvoke(server, new AsyncCallback(EndGetServerInfo), ad); }

private void EndGetServerInfo(IAsyncResult iar) { AsyncDelegate ad = (AsyncDelegate)iar.AsyncState; ArrayList a = ad.EndInvoke(iar); }

private ArrayList GetServerArray(string server) { ArrayList a = new ArrayList(); // this code establishes a SQL connection, executes a // few queries and .Adds the results to the ArrayList return (a); }

In this code, GetServerInfo executes the "GetServerArray" routine asynchronously. This routine basically connects to a SQL Server, executes a couple of SELECT statements and returns the results in an ArrayList. After completion, the EndGetServerInfo is called, and I retrieve the results via .EndInvoke.

Everything works great, and I get my ArrayList of information, but there's one small problem: in the EndGetServerInfo callback routine, I need to retrieve not just the returned ArrayList, but also the initial parameter I passed into the "GetServerInfo" routine (i.e., the "string server"
variable).

I imagine there's an easy way to do this via the IAsyncResult, but I'm not sure how. Any ideas? Or would it be easier just to have my "GetServerArray" routine .Add the value of the "server" variable as the first item on the returned ArrayList? Seems kind of hokey, and would like to avoid that if possible.

Thanks,
Michael C., MCDBA

---
Incoming mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.760 / Virus Database: 509 - Release Date: 10/09/2004

[microsoft.public.dotnet.languages.csharp]

Michael C · Sep 13, 2004

The only problem is that currently my AsyncState is "ad", which returns my
ArrayList results from the procedure I'm calling. If I replace the "ad"
with the server name, I lose my actual results. I thought maybe there was a
simple solution, like a property I was missing or something... Maybe the
correct solution is to return an array of Objects, like this:

o[0] = (string) "servername"
o[1] = (ArrayList) results

That, or just Add the server name onto the ArrayList as the first item as
soon as I enter the GetServerArray function.

Thanks,
Michael C., MCDBA

Richard Blewett said:
There is no automatic way to do this AFAIK but there is a mechanism available.

ad.BeginInvoke(server, new AsyncCallback(EndGetServerInfo), ad);

This last parameter is the AsyncState - you can pass anything in here so

pack up your parameters in an object and pass it this way. Now the issue is
"how do I get the delegate instance to call EndInvoke?"

Well it is documented (and therefore you can rely on it) that the

IAsyncResult you get in a AsyncCallback is actually an AsyncResult instance.
This class is in the System.Runtime.Remoting.Messaging namespace (where else
;-) ). So you can write your callback as follows:

Void Callback( IAsyncResult iar )
{
AsyncResult ar = (AsyncResult)iar;

AsyncDelegate mydel = (AsyncDelegate)ar.AsyncDelegate; // AsyncDelegate is a property on the AsyncResult

MyParamsObject mp = (MyParamObject)ar.AsyncState;

...
}

HTH

Regards

Richard Blewett - DevelopMentor
http://staff.develop.com/richardb/weblog
?
nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/
Hi all,

Is there an easy way to get the parameters of an asynchronous delegate

call from the callback function? Here's an example of what I'm trying to do:

private delegate ArrayList AsyncDelegate (string server);

private void GetServerInfo (string server) { AsyncDelegate ad = new

AsyncDelegate(GetServerArray); IAsyncResult iar = ad.BeginInvoke(server, new
AsyncCallback(EndGetServerInfo), ad); }

private void EndGetServerInfo(IAsyncResult iar) { AsyncDelegate ad =

(AsyncDelegate)iar.AsyncState; ArrayList a = ad.EndInvoke(iar); }

private ArrayList GetServerArray(string server) { ArrayList a = new

ArrayList(); // this code establishes a SQL connection, executes a // few
queries and .Adds the results to the ArrayList return (a); }

In this code, GetServerInfo executes the "GetServerArray" routine

asynchronously. This routine basically connects to a SQL Server, executes a
couple of SELECT statements and returns the results in an ArrayList. After
completion, the EndGetServerInfo is called, and I retrieve the results via
..EndInvoke.

Everything works great, and I get my ArrayList of information, but there's

one small problem: in the EndGetServerInfo callback routine, I need to
retrieve not just the returned ArrayList, but also the initial parameter I
passed into the "GetServerInfo" routine (i.e., the "string server"

variable).

I imagine there's an easy way to do this via the IAsyncResult, but I'm not

sure how. Any ideas? Or would it be easier just to have my "GetServerArray"
routine .Add the value of the "server" variable as the first item on the
returned ArrayList? Seems kind of hokey, and would like to avoid that if
possible.

Thanks,
Michael C., MCDBA

---
Incoming mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.760 / Virus Database: 509 - Release Date: 10/09/2004

[microsoft.public.dotnet.languages.csharp]

Richard Blewett [DevelopMentor] · Sep 13, 2004

I already explained how to get hold of your async delegate instance without passing it via the AsyncState. Look for the section of my reply about the System.Runtime.Remoting.Messaging.AsyncResult class

Regards

Richard Blewett - DevelopMentor
http://staff.develop.com/richardb/weblog

nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/
The only problem is that currently my AsyncState is "ad", which returns my ArrayList results from the procedure I'm calling. If I replace the "ad"
with the server name, I lose my actual results. I thought maybe there was a simple solution, like a property I was missing or something... Maybe the correct solution is to return an array of Objects, like this:

o[0] = (string) "servername"
o[1] = (ArrayList) results

That, or just Add the server name onto the ArrayList as the first item as soon as I enter the GetServerArray function.

Thanks,
Michael C., MCDBA

"Richard Blewett [DevelopMentor]" wrote in message news:%23gWW%[email protected]...

There is no automatic way to do this AFAIK but there is a mechanism available.

ad.BeginInvoke(server, new AsyncCallback(EndGetServerInfo), ad);

This last parameter is the AsyncState - you can pass anything in here
so

pack up your parameters in an object and pass it this way. Now the issue is "how do I get the delegate instance to call EndInvoke?"

Well it is documented (and therefore you can rely on it) that the

IAsyncResult you get in a AsyncCallback is actually an AsyncResult instance.
This class is in the System.Runtime.Remoting.Messaging namespace (where else
;-) ). So you can write your callback as follows:

Michael C · Sep 13, 2004

Yeah, thanks for that. So I went ahead and inserted the server name at the
top of the ArrayList that's returned.

Thanks,
Michael C., MCDBA

Richard Blewett said:
I already explained how to get hold of your async delegate instance

without passing it via the AsyncState. Look for the section of my reply
about the System.Runtime.Remoting.Messaging.AsyncResult class

Regards

Richard Blewett - DevelopMentor
http://staff.develop.com/richardb/weblog

nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/
The only problem is that currently my AsyncState is "ad", which returns my

ArrayList results from the procedure I'm calling. If I replace the "ad"

with the server name, I lose my actual results. I thought maybe there was

a simple solution, like a property I was missing or something... Maybe the
correct solution is to return an array of Objects, like this:

o[0] = (string) "servername"
o[1] = (ArrayList) results

That, or just Add the server name onto the ArrayList as the first item as

soon as I enter the GetServerArray function.

Thanks,
Michael C., MCDBA

"Richard Blewett [DevelopMentor]" wrote in message news:%23gWW%[email protected]...

There is no automatic way to do this AFAIK but there is a mechanism available.

ad.BeginInvoke(server, new AsyncCallback(EndGetServerInfo), ad);

This last parameter is the AsyncState - you can pass anything in here
so

Click to expand...

pack up your parameters in an object and pass it this way. Now the issue

is "how do I get the delegate instance to call EndInvoke?"