Is there any way to override the drag/drop or copy/paste behavior of an existing app in Windows?

Question

I would like to extend some existing applications' drag and drop behavior, and I'm wondering if there is any way to hack on drag and drop support or changes to drag and drop behavior by monitoring the app's message loop and injecting my own messages.

It would also work to monitor for when a paste operation is executed, basically to create a custom behavior when a control only supports pasting text and an image is pasted.

I'm thinking Detours might be my best bet, but one problem is that I would have to write custom code for each app I wanted to extend. If only Windows was designed with extensibility in mind!

On another note, is there any OS that supports extensibility of this nature?

Answer 1

Well, think of this from the point of view of the app designer. If you wrote an application, do you want users to be able to inject things into your application (more importantly, would you want to incur the support/revenue headache of clueless users doing this and then blaming you)? Each application's drag and drop infrastructure is written specifically for the application, not to allow you to drop anything you want onto it (potentially causing crashes and all sorts of other nasty behaviour when you drag something onto an app that simply can't handle it). Stuff like this is hard to do for a reason.

It is possible to do, but it's a lot of work: you need to acquire the window handle of the thing you want to drop something onto, and then replace that window's message handler with your own. That's fraught with danger, of course, since you either have to replicate all of the existing functionality of that window yourself, or risk the app not working correctly.

Answer 2

Yes, I understand that this may have terrible usability implications, but it would be extremely useful to be able to do this for an app I'm trying to write. Its the sort of thing where I don't care if edge cases fail because the basic functionality I'll gain will far outweight it, don't really care whether other people want to use this thing or not.

Is it really necessary to re-implement the window's entire message handler? Is there not some method of wrapping the window's message handler and passing things I don't want to handle back and forth through the wrapper?

Answer 3

If you're willing to do in-memory diddling while the application is loaded, you could probably finagle that.

But if you're looking for an easy way to just inject code you want into another window's message pump, you're not going to find it. The skills required to accomplish something like this are formidable (unless someone has wrapped all of this up in an application/library that I'm unaware of, but I doubt it). It's like clipboard hooking, writ-large: it's frowned upon, there are tons of gotchas, and you're extremely likely to introduce significant instability into your system if you don't really know what you're doing.

Answer 4

Hm thats really too bad. I suppose there are sometimes reasons why apps don't exist yet. Basically what I'm trying to do is simplify the process of sending image links to people using various apps (mainly web browser text forms, but also anytime I'm editing in a terminal window) by hooking the process of pasting an image in a text context, uploading the image in the background, and pasting a url to where the image was uploaded all with a single action.

Edit: I suppose the easier solution to this is to just create a new keyboard combo that is hooked by my app before it gets to any other app. There's no reason in particular that I need to tie it to copy/paste functionality.