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I have a custom rotary slider control inheriting from CSliderCtrl. Its own behaviour is fine, it displays as I want, responds to mouse dragging and rotates just as it should. Then I want to interact with it from its parent dialog and the problems start.
I had imagined that I would just have to trap the ON_VSCROLL message to obtain its value as it changes. (It is set up with Orientation: Vertical though I have tried Horizontal too.) I can't trap ON_VSCROLL or ON_HSCROLL with either setting. I have tried catching NM_RELEASEDCAPTURE and can't get that either. I have:
declared and defined in my dialog .h and .cpp files. They exist as temporary function stubs with a little junk code in there to just see whether I can hit breakpoints in the functions. None get hit.
In the dialog editor the wizard shows only four control events available for the control, NM_CUSTOMDRAW, NM_OUTOFMEMORY, NM_RELEASEDCAPTURE, NM_THEMECHANGED. I expected to see more than that! I would have thought at least I could have accessed ON_VSCROLL via the wizard though a standard CSliderCtrl shows the same four options.
I know sometimes these controls can be a little eccentric but I thought this would be pretty plain sailing. I've dug around and found a couple of suggestions that I'm not the only person to have this issue with a Custom slider but no one seems to have a solution, only to use ON_HSCROLL or ON_VSCROLL which I can't seem to do. This must be something very simple I am seeing wrong. Can anyone suggest what I am missing?
I found that Richard, MSDN is the first thing I go to. There is a wealth of stuff with examples (that actually are only part complete) in there. None of it seems to work!
From your link:
A slider control notifies its parent window of user actions by sending the parent WM_HSCROLL or WM_VSCROLL messages, depending on the orientation of the slider control. To handle these messages, add handlers for the WM_HSCROLL and WM_VSCROLL messages to the parent window. The OnHScroll and OnVScroll member functions will be passed a notification code, the position of the slider, and a pointer to the CSliderCtrl object.
It just seems to back up everything I have done so far. I am trying unsuccessfully to catch the ON_HSCROLL and ON_VSCROLL messages in the parent wiondow just as MS says. I know I can parse out the info once I have caught the message, it's getting the message to land that I can't do even though I seem to be doing exactly what they say.
Looking at CDialog, it does not look like it implements the OnXScroll methods, so one wonders whether it just ignores scroll messages. I'm not sure quite how to get round that (years since I did MFC), but in Win32 I would probably subclass the Dialog control and use my own message handler.
I seem to have at least found a way of doing what I want, even though it does not explain to me what I am really doing wrong here. I have defined a custom message and can send this on to the dialog from within the custom slider at an opportune point. I pass the ID and the value I want as its parameters. I can then catch the custom message in my dialog message handler just as I should be able to and process it from there.
I would still like to know why I can't get to grips with the ON_VSCROLL way of doing this as every link I find tells me I should be able to do this as the standard method. I take your point that CDialog doesn't seem to support OnXScroll, but it's a mystery as to why everyone seems to tell you that is the way to do it. Thanks for your time and efforts Richard, even though we still seem to have only half a picture it's greatly appreciated.
The linker message is just going to say no body for prototype function found.
The ".H" file contains a prototype header, however the ".c"/".cpp" file contains no body code for that prototype.
So the compiler will basically see a forward declaration of a prototype which it will connect but when it gets passed to the linker it can't match the forward declaration to a code body and so it will report that accordingly.
The MSDN blog describes the problem they forgot to cull the prototype header before they got locked for compiler release.
I am using CCriticalSection and CSingleLock for synchronization purpose.
Is there a mechanism to test the synchronization object to know whether it is locked from another thread?
That is, I don't want to enter the lock, but just want to know whether the synchronization object is locked or not without blocking my code.