Overrided TForm.DestroyWnd is not executed

[ertank 27]

Hello,

 

I have found that stackoverflow code of @David Heffernan

https://stackoverflow.com/questions/4354071/how-can-i-allow-a-form-to-accept-file-dropping-without-handling-windows-messages

 

Attached is a project where I put it all together for my use case. However, it seems to leak some memory. I do not know why but TForm2.DestroyWnd seems not executed at all.

 

I simply run and close the application without doing anything. Below dialog is my leak report message

 

Any help is appreciated.

 

Thanks & regards,

Ertan

DragDrop.7z

Edited November 19, 2019 by ertank
Changed title

[David Heffernan 2345]

The code in the linked SO answer doesn't leak. 

 

Update: Er, it does leak. I updated it to override CreateWindowHandle and DestroyWindowHandle, as per discussion below. 

 

Sorry!! 

Edited November 19, 2019 by David Heffernan

[ertank 27]

I do debug run and execution does not stop at first line of DestroyWnd procedure at all.

[David Heffernan 2345]

You can presumably remove the drop target code and just create and free a TObject instead to show that the issue is not in the drop target code. 

 

Making a minimal example is really useful. 

Edited November 19, 2019 by David Heffernan

[Stefan Glienke 2002]

The point is that DestroyWnd is never called on the TForm (tested with 10.3) thus FDropTarget never destroyed.

[David Heffernan 2345]

2 minutes ago, Stefan Glienke said:

The point is that DestroyWnd is never called on the TForm (tested with 10.3) thus FDropTarget never destroyed.

Indeed. So one wonders why. 

[David Heffernan 2345]

I haven't got time to look at this in VCL code, but my guess from memory is that you need to be overriding CreateWindowHandle and DestroyWindowHandle instead of CreateWnd and DestroyWnd. 

 

CreateWindowHandle and DestroyWindowHandle are the methods tasked with he actual creation and destruction of the window. 

 

Probably when the form is torn down it just calls DestroyWindowHandle and not DestroyWnd. 

Edited November 19, 2019 by David Heffernan

[Stefan Glienke 2002]

Because!

[ertank 27]

4 minutes ago, David Heffernan said:

I haven't got time to look at this but my guess is that you need to be overriding CreateWindowHandle and DestroyWindowHandle instead of CreateWnd and DestroyWnd. 

 

CreateWindowHandle and DestroyWindowHandle are the methods tasked with he actual creation and destruction of the window. 

That did solve my problem.

[pyscripter 689]

See my post on this very topic.