Accessing imaq objects using pointers

Question

I defined a CWIMAQ control object in my application's view class using the visual C++ Resource View dialog builder utility. I also defined a generic class to acquire and process the images from the 1428 frame grabber card. When I create the generic class object in the application's view, I pass a pointer to the view to the generic class's constructor.
When the generic class tries to acquire an image using the CWIMAQ object defined in the view using the View pointer I get a windows error.
//MFC view class
CMyView:nInitDialog(....)
m_processImage=new CProcessImage(this);
//generic class
CProcessImage::CProcessImage(CMyView* view)
m_viewPtr=view;
CProessImage::CProcessImage()
m_viewPtr ->
m_cImaqObject.AcquireImage(); //this fails
If I put the AcquireImage function call inside the view it doesn't fail. But then when I try to get my images from the buffer from my genric processing class I get the same error. So I really need to figure out how to access the CCWIMAQ object from other classes. How can I call the AcquireImage function from my worker class?
Thanks for your help

Answer 1

The error message you are getting is the result of a breakpoint being hit. If you run in the debugger, you will see where the breakpoint is in your code. I suspect that you are hitting a breakpoint as the result of hitting an assert in the MFC source code.
Without running this myself, I can only speculate as to the cause. From what you describe, one thing I would look to is whether the view HWND is being created before you attempt to access the control in the failure case. You are hosting the ActiveX control on the view window (even though it doesn't draw). Consequently, the control still needs an HWND (I believe). If the view window has not been constructed, the control cannot be properly hosted. MFC might detect this and assert, causing th
e breakpoint that you are seeing. One way to try this out would be to delay calling into the ActiveX control until you are certain that the view window has been constructed.
Also, I'm having some trouble figuring out what you're showing with the example code you posted. Your code shows 2 constructors, one of which takes the view pointer and one of which doesn't and instead calls m_viewPtr->m_cImaqObject.AcquireImage(); If this latter constructor is the one that fails, how are you initiailizing the m_viewPtr? Another point of confusion for me is that your code shows CMyView:nInitDialog, but CFormView doesn't have an OnInitDialog - do you mean OnInitialUpdate or something else?
If none of this helps, could you post a .zip file with a stripped-down version of your project that demonstrates the problem?