Is there a way to know when another hwnd has closed?

Question

Is there a method for setting up a listener/watcher to know when an unrelated application window is closed?

I can check to see if the window is still open, but that seems silly to continually do.

If the other app is not yours, you may need a system wide CBT hook. — user1793036, Mar 07 '14 at 00:10

score 5 · Accepted Answer · answered Mar 07 '14 at 11:38

5

The Accessibility API's SetWinEventHook filtering for EVENT_OBJECT_DESTROY.

This is notification based so no polling and unlike a CBT hook does not require injection.

answered Mar 07 '14 at 11:38

Alex K.

Thank you, this is the simple answer I was looking for. – Meep Mar 08 '14 at 19:04

score 4 · Answer 2 · answered Mar 06 '14 at 16:57

4

You can:

poll for HWND validity (esp. if you don't need timing precision)
subclass the window to intercept its WM_DESTROY and then forward the notification to your app
install a window message hook to be able to intercept the message otherwise
create a hidden child window to get it destroyed with the parent destruction, to also have your message handler called on time for you

answered Mar 06 '14 at 16:57

Roman R.

I should have said it is an external application, I just need to know when it closes, but I cannot edit it. – Meep Mar 08 '14 at 19:03
1

Like any other handle type, `HWND`s get reused. Checking the validity of a `HWND` does not answer the question whether a window that had a particular `HWND` at the time of retrieval is still alive. – IInspectable Jan 29 '15 at 15:47
@IInspectable: It is a good point and in fact polling is not a reliable solution. Still API to check `HWND` value validity is here, it is simple and straightforward, and then sometimes one can accept the chance of mistake and prefer simplicity. – Roman R. Jan 29 '15 at 16:15

2 Answers2