SAMPLE: CFormView-Based Server Shows Metafile When Not Active

• The Microsoft Foundation Classes (MFC) included with: - Microsoft Visual C++, 32-bit Edition, versions 4.0, 4.1, 4.2, 4.2b,

       5.0
  

SUMMARY

The FVServer application demonstrates using a CFormView based application as an OLE server object. One of the problems using CFormView is that the dialog-based view will not render itself into the metafile used to display the application when it has been in-place activated and then deactivated.

This sample demonstrates one method of overcoming this limitation.

The following file is available for download from the Microsoft Software Library:

 ~ Fvview.exe (size: 79441 bytes) 

   ARTICLE-ID: Q119591
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MORE INFORMATION

When you base your server on the CFormView class, you create a dialog template with the resource editor to act as the view of the application. If you activate the application in-place, the drawing occurs in the CFormView::OnDraw(). Usually the CFormView derived class does not implement any drawing.

When the user selects outside the in-place activation area the application goes to the loaded state and any representation on the screen is handled by rendering a presaved metafile. This metafile is created in the COleServerItem::OnDraw() by passing in a device context (DC) for a metafile and expecting the drawing to occur. In most cases the CView derived class's OnDraw() or a separate function is called to actually render into the metafile. See the Scribble tutorial for an example of how to accomplish this.

In the case of a CFormView-derived class, this technique will not work directly. One method of overcoming this limitation is to draw each of the controls yourself. Some controls may not draw and you may have to use GDI calls such as Rectangle() and LineTo() to actually draw the control.

Another method, which is demonstrated in this sample, is to BitBlt a picture of the screen into a memory device context and save it. Then, when the COleServerItem::OnDraw() is called, BitBlt the saved picture into the metafile DC provided. The side benefit to this method is that you get a Print Preview of the object for free from MFC, because it uses the same metafile.

In the sample, the function CFVView::SetPicture() dynamically creates a memory DC and a bitmap object. The bitmap object must be set to the size of the current view before it is selected into the DC. This is accomplished by setting a member variable in the document class to the size of the view after the view is created. In the sample, the size is computed from the size shown by the resource editor and uses hard-coded values. This seems reasonable as long as you are not dynamically changing the size of the dialog. See the documentation on CFVDoc::OnNewDocument() for the method used to get the size in pixels of a dialog (also see KB article Q125681).

The only problem remaining is determining when the SetPicture() function should be called. There are two locations. The first is in the COleServerDoc derived class's CFVDoc::OnDeactivate(). This function is called twice after the user selects outside the server's in-place activation area. The first call is when the server is going from the UIActive state to the Active state, and the second call is going from the Active state to the Loaded state. We must distinguish between these two calls because the first time it is called, the CFormView is visible and the second time it's called, it is not visible. The server's DoVerb() is called to hide the server between calls to OnDeactivate(). If we simply called SetPicture() during OnDeactivate(), we would BitBlt a blank picture over the good picture in the second call. Simply setting a switch solves that problem.

The second place to call SetPicture() is in CFVView::OnActivateView(), an override of the CView method. Check to make sure the view is being activated, and then call SetPicture(). This last call is necessary for embedding in Microsoft Excel, for example. Microsoft Excel does not deactivate the server such that OnDeactivate() is called.

You must also handle the OnGetExtent() to set the initial size of the CFormView application and handle OnSetExtent() to receive size changes. You should also reset the size when the CFormView::OnSize() is called. If you do not care to react to sizing changes these last calls are not necessary. The sample handles some sizing problems, but not all. Disabling sizing should be straight forward to accomplish.

You must also notify the container whenever the data changes. In this simple application, NotifyChanged() is called in the SetPicture(), so any time the application changes what the user is seeing, call SetPicture(). There may be other places where NotifyChanged() should be called. If you call NotifyChanged() without calling SetPicture(), you will get the last metafile that was saved and it may not show the current state the user sees.

This application is not "bullet-proof", but is instead a starting point for further development.

REFERENCES

"Inside OLE", second edition, by Kraig Brockschmidt. "OLE 2 Programmer's Reference, Vol 1"