I am trying to write a code to check previous instance of the application in vb.net, my requirement is that application should prevent for same user and it should allow for different user who wants to access through remote parellel 2x client..Any one please help me on this...Thanks
If you are using VB.Net, You should definetly look into WindowsFormsApplicationBase class, shipped as part of .NET framework.
There is a property (IsSingleInstance) specifically designed to provide single instance behavior to the application.
You can even receive notifications through StartupNextInstance or the counterpart OnStartupNextInstance method when another instance of the application tries to run.
I forgot to mention that My.Application already is an object of the WindowsFormsApplicationBase type (at least in VB.NET WinForms applications).
UPDATE:
Currently, to take advantage of this stuff from a VB.NET project you have to follow these steps:
Edit project properties.
Enable "Make single instance application".
Click "View Application Events".
(optionally) Implement StartupNextInstance event handler.
Related
We are using a 3rd party ActiveX control in our application, recently as per our request they have added new function in ActiveX control interface and we are trying to access those function in our application. Due to some reason there are chances where we can not deploy our 3rd party ActiveX control but we are deploying our application. So old 3rd party ActiveX does not have new functions but our application which is consuming those function are trying access new function. Because of that we are getting some inconsistent behaviour lIke crash or message error box.
So we wanted to understand that is there any way to determine function of 3rd party ActiveX control exist or not in our application ? So based on that we wanted to avoid calling those function.
Thanks.
Well, you can get the type library information and try to read and walk it to determine if the function exists.
Or, you can call the function through IDispatch::Invoke and see if it fails. If it fails, don't call it again and call the fallback function.
So, it doesn't have a separate Guid for the two different interfaces? Technically, it is supposed to...but sometimes vendors don't provide new Guids for updated interfaces....I plead the 5th.
The way it is supposed to work is the you QueryInterface for the interface you want and use it.
Wonder if anyone can help me as i'm getting the following error 'Could not find endpoint element'.
My setup is similar to the following - A main project vb.net (Starts with say a login.exe that in turn uses class libraries to then do things such as set the menu navigation system which proceeds to call several winform class libraries) One of my winform class library calls another class library which contains some logic that will then in turn call a class library that has the service reference to a WCF service and will handle the WCF service reference function calls.
So if i run my winform as a standalone exe rather than a class library contained in the above setup everything works fine with connecting to the web service contained within the class libraries because i have added the <system.serviceModel> reference information to my winforms app.config as per the below thread suggested.
"Could not find endpoint element with name..."
My issue is that once i turn my winform back to a class library and include in my main project to be called it never finds the the <system.serviceModel> reference contained within my winform .dll as i'm lead to believe by again by the above linked post it will use the main project app.config not my winforms configuration.
What im trying to get at is I don't really want to add the <system.serviceModel> information contained in the app.config of my winform dll to the starting login.exe(being the program that starts the chain) as that just seems messy and just strikes me i must be doing somthing wrong in the first place. Is there a way to use the setting from my winform class rather than going all the back back through to the main project??.
I hope that makes some sort of sense any help would be greatly appreciated as really stuck as a wcf newbie, thanks in advance
Personally I don't think it's messy, that is generally how these things are done there is an application configuration file for your main you only have one copy of your main and usually your application is installed only once meanwhile you could have lots of copies of your DLL used by many apps... The configuration file will usually always contain settings that pertain to that one application meanwhile a DLL could be used by multiple applications. In short you should use the main app.config.
In any case to answer your question you could read in the app.config of the DLL in like any normal file parse it and programmatically setup the end-points as described here:
How to: Create a Service Endpoint in Code
I don't usually program in the .NET framework however I've needed to use it to create a simple exe application that logs data from some measurement equipment. I want this application to have an automation interface with a couple of methods. I've done this before using Delphi/Pascal and it was very straightforward, and I can create a Class Library in Visual Studio that registers itself and the methods and can easily be interfaced with but adding a ComClass to the windows form application doesn't work, can anyone point me in the right direction?
This started as a comment but just kept growing, hopefully i am not off track ...
You can only register a dll. So the short answer would be to add a class library to your project and put the com class in there. This would allow you to share the functionality of the class, but not the same instance of that class.
I think your problem is that you are trying to establish Interprocess Communications. My immediate suggestion is not to do that, at least at first.
For a start you could have your com app interface with a .net class library which would log data. You could then have another project with a .net executable that displays the log, and updates periodically. Now you have .net code on both sides of the fence and can start investigating ways to get them to talk to each other.
The hard part is invoking methods and returning values. If you really need a responsive system you can investigate named pipes inter-process communication, or using a WCF service with callbacks between the two systems. The problem is that in either case you are hamstrung by the class library not being hosted by .net so you have limited functionality (no config file etc). If you can put up with a time lag I would suggest simply starting with writing messages to a local datastore and then polling from each client, every 30 seconds or so. For example the app would create a message saying "give me measurement A" and then start polling every second. The DLL would have a timer and within 30 seconds would read that message and write its own message with the measurement, which the EXE would read and then display. Once you get that system up and running you can decide whether you need to tackle inter-process communication, which is really just a different interface.
We are adapting our client side relatively complicated application (ActiveX / .net / Delphi / C++ / COM ) to use SxS to achieve non admin deployment and isolation from older versions of our product.
We were able to achieve this goal for almost all our in proc components such as our .net ui, Delphi ui, and the COM servers we use in proc by composing a manifest file which described all the libraries used by our process, with no registration on the client of any of the components (almost).
And here comes the almost part:
At the moment, our application invokes (from it's c++ portion) an out of proc ActiveX server (Delphi ActiveX EXE), which in turn itself invokes another set of out of proc ActiveX servers (third party plugins, any thing goes here, Delphi, C++, any thing as long as it's out of proc ActiveX EXE and implements our interfaces).
As we know SxS does not support out of proc ActiveX servers. And we can't use these objects as in proc com servers in our main process because that would require a major rewrite of our application and even worst, a break of our public facing API which is used by third party tools and vendors, an api break which we can't allow.
We have stumbled on this article which describes how IHTMLDocument2 can be extracted from an Internet Explorer window running in a separate process. Which made us think of this approach:
We would create a secondary satellite application / process which will run the ActiveX as in process server.
Then we will use LresultFromObject and ObjectFromLresult to transfer a reference of the ActiveX object from the satellite application to the main application process. The satellite application will have it's own manifest file which will allow it to run in SxS mode.
Same approach will be taken to communicate between this Delphi ActiveX EXE and the third party AciveX EXE Plugins
There is an alternative solution, which for the moment we do not prefer over the proposed solution above which is to use .net remoting and .net com proxy classes to open the communication channel between the two processes, by translating the com request to .net remoting, and back to com on the second process.
So here comes the question:
What do you think about this approach ?
Do you see a better solution to the problem ?
It is possible to do. What is needed:
An application needs to start a server itself rather than relying on COM to do it. You don't need the extra indirection provided by the registry, just use CreateProcess().
A server should register its class factories in its main() method with CoRegisterClassObject().
Important: the CLSID it uses for each factory should be altered to be unique for each service instance. This ensures that the client connects to the correct server. I simply XOR the process ID with a class factory CLSID. The client knows the process ID as well so can make the same alteration.
The application should call CoCreateInstance() in a loop with a Sleep() call to wait for the object factory to appear. Don't declare failure until at least 60 seconds have passed (that bit me).
Both the application and the server need a manifest that contains a <file> element for each proxy/stub DLL and <comInterfaceExternProxyStub> elements for each interface that is remoted.
Alex,
nobugz is right, you can access the Running Object Table to create an instance of a COM Object from a currently running process of your Delphi automation exe.
However I have found a big issue that I cant explain. I can only access the object via the variant dispatch method when working this way.
Basically if my Active X exe is not registered, I get an "Interface Not Supported" error if I try to instance the object through interfaces for example:
WebUpdate : IAutomation;
WebUpdate := CoAutomation.Create; <-- Wont Work Error
WebUpdate : Variant;
WebUpdate := CreateOleObject('WebUpdate.Automation'); <-- Works Fine
If I register the active x exe using regserver the problem goes away!!
Go Figure!
I'm creating a Windows Console application written in VB.NET and I have a few processes that need to be called only once during the lifetime of the application. If it was an ASP.NET application, I put these in the Appliction_Start method of the Global.asax.vb file. Since there isn't a Global.asax.vb for Console applications, is there an event I could handle that allows me to call my functions before Main is called?
Is there a problem with just calling them first in main?
Main is the first method where you can grab the needed information / inizialize global stuff.
Why would you need an earlier point? The only thing that is different to Application_Start is that no other method is called automatically (unlike in a web application where the site is opened and the code executed).