> Does it start a new process from the file the window's existing process is based on? This would rely on that program recognizing it's already running and sending a message the other instance to open the dropped file then exit.
You make it sound like this is somehow crazy complex behavior that no one would have implemented, but this is table stakes for a Windows application as otherwise double-clicking files that are supposed to open in your program wouldn't work.
Task bar items don't represent exe files, they represent windows spawned by process started from exe files. Excel has many different behaviors depending on how you open a file. In fact, you can get excel into a state where double clicking a file opens in a hidden instance of excel that you can never see.
If you drag a file to a notepad window taskbar item, should it open in that window? should it open a new window in that process? Should it start a new process with that file? Should users have control over how that happens or should application developers? Or both? Or Microsoft?
On macos, theres only ever one instance of an application open so these questions are easy answer. On windows, they arent.
it's not that complex. If you drag it to the notepad icon, it opens a new process. If you drag it over the icon and then over to one of the small window previews that pop up, it sends the file to that window
You make it sound like this is somehow crazy complex behavior that no one would have implemented, but this is table stakes for a Windows application as otherwise double-clicking files that are supposed to open in your program wouldn't work.