How do I intercept Windows events with C#?

Question

I have a commercial logging application which sends data to a remote server. If it loses contact it displays a message box with an error message. It is being used in a system where the link is not continuously present so it is frequently popping up pointless and annoying messages. The data is cached so there is no problem with losing it. I have written a small C# app which can successfully detect the message boxes and kill them trouble is it needs to poll continuously which consumes PC resources and still allows the pop-ups to appear between polls. What would be great would be some way to get C# to detect the Windows form-load events and immediately issue a kill command.

Sam Hobbs · Answer

So you don't have access to the soruce code of the application? Do you understand what an address space is? If not my article about virtual memory might help. Are you able to execute anything in the address space of the application showing the form? Please do that if possible; I will try to help with that if needed. You can use the Windows API function SetWindowsHookEx. You will want to set the dwThreadId to the thread in the other application. I don't know if the hook must be in a separate DLL but if so then that DLL cannot be written using .Net so no C# for the DLL. Since the hook will be thread-specific you might be able to make the hook using C# but I am not sure. Another more advanced option would be to inject a DLL into the other address space but the DLL would have to be written without .Net and is not likely to be needed for this and is very adavaced to do and antivirus programs would need to be told to allow it.