Not receiving MouseWheel message because focus is removed from control

Question

I am trying to implement some mousewheel interaction as can be seen in e.g. Visual Studio. When the mouse is over a control and the mousewheel is scrolled the control under the mousewheel is scrolled instead of the control that has focus. I do this by adding
a MessageFilter (but also tried a WH_CALLWNDPROC hook) and detecting the WM_MOUSEWHEEL message as it passes and pass it to the control under the mouse cursor. This all works as expected when at least one of the form controls have focus, however sometimes the
focus is lost fi when a control in a container is disabled and there are no other enabled controls in that container. In that case the WM_MOUSEWHEEL event is never send and it doesn't work anymore.
To test this behavior I created a test application that contains a message filter and a control that is derived from UserControl. That control contains a button that will have focus. Then the button Click event will disable the button itself. After
that the focus is lost and WM_MOUSEWHEEL isn't received by my filter anymore.
So how can I make sure that the WM_MOUSEWHEEL is always send by a) always have a focused control (how do I do this)? b) is there another way to intercept WM_MOUSEWHEEL even when no control is focused?

Answer 1

I agree with you that is an issue we need to deal with...
Is this a bug in .NET? Why is the keyboard focus set to a control (as we can use TAB to navigate) but Windows doesn't know it has a focused control?
...I added a line inside that method to get the control's parent focused, you could have a try.
Your idea does work, however this application is just for reproducing the problem. The real application is much more complicated, but I have implemented a workaround. It is something like:
void UpdateControls()
    var hadFocus = containerControl.ContainsFocus;
    containerControl.Controls.UpdateVisualState();
    if (hadFocus && !containerControl.ContainsFocus)
        containerControl.Focus();
I think there could be a lot of other situations that could result in a loss of focus. I wouldn't like to write these kind of workarounds for each case. Isn't there a somewhat more robust solution to this problem? How does Visual Studio make sure that there
is always a control with focus? I mean I don't see any problems occur in the IDE of Visual Studio where the mousewheel isn't working because of focus loss.
Hello,
The workaround you shared works and I agree with you that we could be sure that usercontrol could get focus but it seems like that usercontrol doesn't get any focus.
To confirm whether there is any way to solve this issue and submit this issue to product team, I would recommend you submit a feedback in
http://connect.microsoft.com. 
You could share the link of your feedback here that we could help you vote it. I think that Microsoft engineers will evaluate them seriously and provide you better support. In addition, you can post the answer here once the issue is resolved.
Thanks for your sharing and understanding. 
Best regards,
Carl
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