(Shone)
7/22/2004 2:09:00 AM
Hi,
my idea is to establish a simple communication between appA, app1 and
app2, or better to say CONTROL the app1 and app2 from applicationA.
All of those are WinForm apps.
AppA should be able to query app1 and app2 for some simple info, like
the status of those applications, and also to shut them down if
needed, i.e. issue the command to applications to shutdown themselves.
The research on how to accomplish this brought me to .NET Remoting, so
I've decided to try it out.
First thing I learned about Remoting is that initiating application
should be the client, while the application that "listens" for remote
calls, and responds to them is the server. In my case that would make
the appA the client and app1 and app2 the servers, since the appA will
be the one always initiating the remote contact. And that's what I
did, allthough already here I think I made mistake, because it's
unusual to have 1 client and 2 servers (and even more, because
eventually there will be app3, app4...). So what's the better solution
for the problem I need to solve?
Second problem I had was how to retreive the desired info from the
server, since the server application doesn't instantiate the remoting
class? Namely, the remoting class is defined and registered on the
server, but there is no reference from the class to the Form's
variables, and vice-versa. What I mean, I have the (single) Form code,
and separate remoting-class code, but there is no obvious connection
in executing these two, so that I can for example feed the desired
data from Form to the remoting class and return that data to the
remote-calling client.
I found a solution for this problem by sharing some data on the server
through AppDomain properties, and it's working (amazingly!). I'm sure
that this ad-hoc solution is pretty much unusual, and that there must
be some more common method and right way to do it, so I would like to
hear your expert oppinion about it, please.
The third and most important problem, I still didn't manage to solve
is how to issue a command from appA to app1 (or app2) to shutdown? I
tried with defining and raising the events, but it's not working for
some strange reason. Here's what I did:
1) server side - defined a Delegate and an Event in the remoting
class:
Public Delegate Sub ShutDownEventHandler(ByVal sender As Object, ByVal
e As EventArgs)
Public Class clsRemotingListener
Inherits System.MarshalByRefObject
...
Public Shared Event ShutDown As ShutDownEventHandler
...
I declared Event as Public Shared, because I need to catch this event
on the server, and server doesnt instantiate the remoting object.
2) defined the public method that will raise the event. This method
will be called from the client (appA). This is still in the
clsRemotingListener code:
Public Sub ShutDownServer(ByVal e As EventArgs)
RaiseEvent ShutDown(Me, e)
End Sub
3) in the server code (Form's constructor), I declare the handler for
the event:
AddHandler fRemoting.clsRemotingListener.ShutDown, AddressOf
Me.RemoteShutDown
Here you can see why the Event needed to be "Shared".
(fRemoting is just a name of the separate dll where the
clsRemotingListener is)
4) Finnaly, I define the Form's local RemoteShutDown method:
Private Sub RemoteShutDown(ByVal sender As Object, ByVal e As
EventArgs)
Me.TextBox1.Text = "I AM BEING SHUTDOWN!!!"
Me.Close()
End Sub
So when I try to invoke the "ShutDownServer" method from the client -
it doesn't work. Everything freezes, both client and server, and the
third window pops-up, obviously some error report, but it doesn't even
get to paint itself (remains blank). All that stays like that until I
kill the app1 (server), then the "third window" closes too, and appA
(client) continues to work normally.
I would like to point out that only the server shutdown attempt causes
the problem, not the remoting or event raising/receiving. At least
that's what I think, since everything works great when I comment-out
the "Me.Close()" statement in step 4). Then the server successfully
receives and processes the event, writes out the message, and
everyone's happy (both appA and app1 continue to do their jobs
uninterrupted). But the closing attempt messes everybody up!?!
So if you had enough patience to read so far, I would like to kindly
ask you to give me a couple of guidelines here.
Please don't respond with "it's obvious that you don't understand the
basic principles of .NET Remoting...". First of all that statement
couldn't be more TRUE, second of all - I already know that :)))
All I need is a couple of lines of example code with or without a
short explanation. I believe that I was clear in explaining what my
problem is and that is pretty much basic, so many of you experts in
.NET remoting are already doing that as a routine.
Thank you in advance...
Shone