WPF - HwndSource Hook for a child control with its own handle?

[RoyalcraftDev]

Hello, I'd like to know if it's possible to use HwndSource.AddHook on a custom child control that has its own handle.

For a little bit of context, I have a control which creates a window using CreateWindowEx that is later on rendered in my WPF Window. The issue is that I can't find a way for it to actually handle Win32 messages of the native window I created. I've tried to set the WndProc with SetWindowLong but it only results in a ExecutionEngineException. The exception can also vary. Then I tried to create my own HwndSource but gave me an ArgumentException telling me that it has to be an element without a parent, in other words, the Window is the only thing that can be used for the HwndSource.

So now, is there a way to actually do it similar to how HwndSource works but for child elements?

Note: If you want to reproduce the issue, simply create a WPF project, DLL import SetWindowLong with a WndProc delegate and call it using the window's handle. (This isn't the right method to reproduce my issue.)

IMO, the reason of this behavior is a conflict with the WPF way of handling window messages but I'm no expert on the subject, so I might be wrong.

Update: It seems like I am able to set the WndProc (I tried to set it after initializing the renderer for the surface.)

It crashes because my WndProc is triggered. I tried to remove the code and return nint.Zero, removing the code and returning DefWindowProc but those still trigger the ExecutionEngineException

I set the WndProc this way:

Define it like this:

PInvoke:

[miloush]

Please attach a repro project so that we can see your pinvokes and what you are trying to subclass.

[RoyalcraftDev]

Okay it took me quite a while to reproduce it but now it successfully fails on a new project, I'm uploading it right away!

[RoyalcraftDev]

WpfApp2.zip

[RoyalcraftDev]

Also note, to trigger the issue you need to play a bit with the window, resize, hover, click, etc. With my actual project it's more direct, hovering directly causes the issue but here it's slower for some reasons.

[miloush]

These are symptoms of GC being involved. As @NeverMorewd pointed out below, you have to make sure the pointer you hand to the native code stays valid even when GC moves your WndProc in the memory. Your code is just passing simple pointers that get outdated.

[RoyalcraftDev]

Alright I will take a look and let you know

[NeverMorewd]

You may refer to https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.gchandle?view=net-8.0

[RoyalcraftDev]

Thanks!