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I'm trying to write a simple example program to learn more about using

bitmaps and picture controls. It is a dialog-based program with only two

buttons and one picture control. One button is to display a bitmap, and the

other is to erase the bitmap.

The bitmap is displayed correctly and does erase with the other button,

but I am not able to click on the display button again without an Assertion

Error. Although I have found that if I declare the bitmap locally in the

display button handler and put another bitmap declaration in the erase

button handler, it is possible to click the display button after the erase

button and the bitmap is redisplayed. However when declared locally, the

bitmap is lost if the dialog is covered and then does not repaint the

bitmap. It does repaint when the bitmap is declared in the class

declaration.

So, I would prefer to declare the bitmap in the class declaration, but

what is required to be able to click on the display button again. Code is

below:



void CBitmapTestDlg::OnDisplay()

{

// CBitmap bitmap1; ***remove this***

bitmap1.LoadBitmap(IDB_BITMAP1);

m_bmp1.SetBitmap(bitmap1);

}



void CBitmapTestDlg::OnErase()

{

// CBitmap bitmap1; ***remove this***

DeleteObject(bitmap1);



Invalidate();

UpdateWindow();

}


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Try this



"cdg" <anyone@anywhere.com>wrote in message



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A CBitmap is a "wrapper class" around an HBITMAP handle. Once the association has been

made, you have to break it to allow the CBitmap to be re-associated with a different

bitmap. Your assertion failure is probably because there is still an association. When

reporting an assertion error, it is essential to tell us what file/line it occurred in and

what version VS you are using.



Because the class is a wrapper class, its destructors will delete the associated object,

so when the OnPaint handler is executed, the bitmap is lost. You can break the

association explicitly by using Detach().



See the essays on my MVP Tips site on using bitmaps, and on Attach/Detach.

joe

On Tue, 24 Oct 2006 20:52:23 GMT, "cdg" <anyone@anywhere.com>wrote:



email: newcomer@flounder.com

Web: www.flounder.com">www.flounder.com

MVP Tips: www.flounder.com/mvp_tips.htm">www.flounder.com/mvp_tips.htm

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I tried this and it worked perfectly.



void CBitmapTestDlg::OnErase()

{

DeleteObject(bitmap1);

bitmap1.Detach();



Invalidate();

UpdateWindow();

}





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CStatic::SetBitmap doesn't take ownership of the HBitmap. If you do



CBitmap Bmp;

Bmp.LoadBitmap(IDB_BITMAP1);

m_Static.SetBitmap((HBITMAP)Bmp.Detach());



you are going to end up with a resource leak, because CStatic doesn't delete

the object.



AliR.



"Joseph M. Newcomer" <newcomer@flounder.com>wrote in message



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I don't mean to be stickler here but



Why are using,



DeleteObject(bitmap1);



instead of



bitmap1.DeleteObject();



AliR.



"cdg" <anyone@anywhere.com>wrote in message



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by the way, calling Detach after DeleteObject does not do anything.



And if you want to do this without repainting the entire window do it like

this



void CBitmapTestDlg::OnDisplay()

{

bitmap1.LoadBitmap(IDB_BITMAP1);

m_bmp1.SetBitmap(bitmap1);

}



void CBitmapTestDlg::OnErase()

{

m_bmp1.SetBitmap(NULL);

bitmap1.DeleteObject();

}





AliR.



"cdg" <anyone@anywhere.com>wrote in message



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I just read your post, but if that is the correct way I'll write it with

the dot operator.





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You are right. I tried it and it worked perfectly. And it is a probably a

better approach for this.





"AliR (VC++ MVP)" <AliR@online.nospam>wrote in message



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If you are using a CGdiObject derived class like CBitmap, then

CGdiObject::DeleteObject() would be perfered.



AliR.



"cdg" <anyone@anywhere.com>wrote in message



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