Creating COM Component in .NET to override IE functionality (custom download manager)_问答_开发者

I have to create a custom download manager that will replace a standard download manager in Internet Explorer. After googling I've learned that I have to create a COM component that implements the IDownloadManager interface.

As far as I understand I have to create a dll, generate guid for it and register it using regasm.exe utility开发者_StackOverflow, and then add specific entry in windows registry for IE. I have a few questions:

I want my program to be an exe and I want to be able to run it manualy and add url to it as well as run it by IE after clicking on a downloadable link.

Although I would prefer to have a single executable, I think to achieve this i have to create dll and exe, and from dll i should check whether the exe is running (by window id) and run if it isn't and communicate with it somehow. Is this correct approach?
I want to share my program with other users, and i don't want them to register COM manually. Is it possible to do it from the code? Or perhaps I should create an installer (which I would like to avoid)?

I'll start with a WARNING: Do not create a .Net components that will be loaded in IE. Ask yourself the question "What would happen if another app does the same, and it uses different version of the CLR?". IE does not guarantee any order of loading the different COM components it needs, so there's no guarantee that your version of the CLR will be loaded in the process by the time IE calls you.

Now onto your problem. There are several issue with your scenario:

.Net does not support creating out-of-proc COM components natively. Yes, it is possible to create one by doing bunch of hacks and manual registration; however, it is not a simple task and requires deep knowledge of how COM works;
with the above in mind, your option is really to create a .Net DLL and use the ComVisible attribute to expose the classes you need to COM. As you mentioned it, you will need to register it using RegAsm.exe, for IE to be able to use it;
since you want the main functionality of your download manager to be in a standalone executable, you will have to use a .Net supported cross-process communication mechanism. .Net Remoting is likely the easiest way to implement it, and should for the most part meet your requirements. The alternative is to implement the download functionality in-proc. However, beside the consideration that you now could easily hose the IE process, if you are not careful to listen to its quit notification (which require a lot more work by itself), there's also the whole enchilada with the IE7+ protected mode, which severely limits what your in-proc code can do (limited file access, registry access, Windows APIs and other limitations);
there are certain complications arising from the IE8 and IE9 process model. Besides the top frame process, IE8/9 create a pool of processes and load-balance the tabs into these. I don't know which process will try to create your COM component and wheter it's going to be one per tab or per process or for the whole IE session (which spans multiple processes), so you have to be prepared that you might have multiple instances in multiple processes running concurrently. If this is the case, you will have to figure out how to ensure that the communication between the in-proc COM component and the executable is not serialized one instance at a time, or you might affect the browsing experience for the user. (A simple scenario would be a page with multiple download links and the user right-clicking on each link and selecting Open in new tab, thus launching multiple downloads in several tabs at once);
even if there is one instance per IE session, elevated IE instances run in a separate session from the regular user IE instances for security reasons. There's the interesting complication that your .Net Remoting call from the in-proc COM component in the elevated IE session will result in a second copy of your executable being launched also elevated. Thus, your download manager will have to be prepared that there might be two processes accessing the same download queue;
starting with IE7, IE protected mode (the default) will intercept any calls that result in starting a new process and show a dialog to the user. The only way to avoid this would be to register a silent IE elevation policy for your process. The elevation policies are registered in HKEY_LOCAL_MACHINE, which means that you will need an installer, or at least a simple script for the users to run as administrator;
even if you decide against the elevation policy and to live with the bad experience of this dialog, to register your download manager with IE, you still will have to write to the HKEY_LOCAL_MACHINE registry hive, otherwise IE will not know of it and won't use it. In other words, you still need some kind of installer or a deployment script;
IE is fairly aggressive in measuring the performance of the code that runs on the UI thread and in terminating background threads when exiting the process. So whatever functionality you have in the in-proc component, you will have to balance between being as fast as possible on the UI thread (which means less work or you'll impact the user experience) and doing work on the background threads (which means be prepared you might be killed without notification at any moment);

I think this list covers the main issues you will have to solve. The biggest problem you will encounter is that a lot of the specifics around IE process model are not well documented on MSDN, and there are almost no examples of implementing this scenario in managed code (and of those that exist, most are old and are not updated for IE8/IE9, and some even won't work in IE7).