Microsoft KB Archive/131279

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PRB: SelectObject Fails After ImageList_GetImageInfo

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Q131279

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The information in this article applies to:


 * Microsoft Win32 Software Development Kit (SDK), used with:
 * Microsoft Windows 95

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SYMPTOMS
When you try to select the hBitmap returned by ImageList_GetImageInfo into a device context, the call to SelectObject fails and returns NULL.

CAUSE
Under the debug version of Windows 95, attempting to select the hBitmap returned by ImageList_GetImageInfo into a DC causes the GDI to output the message "Bitmap already selected."

Image lists maintain memory DCs with the image and mask bitmaps already selected. This is done to prevent applications from modifying the images contained in the image list that are currently being used by the system. Because a bitmap cannot be selected into more than one DC at a time, applications that call SelectObject on the same bitmap fail.

RESOLUTION
An application can work around this in Windows 95 by calling CopyImage on the hBitmap, as demonstrated in the following sample code. This API is new for Windows 95. Remember to delete the hBitmap copy when using this function.

Sample Code
  HDC        hDC; HBITMAP   hBitmap, hOldBitmap; IMAGEINFO imageInfo;

ImageList_GetImageInfo (hImgList, iWhichImage, &imageInfo); hBitmap = CopyImage (imageInfo.hbmImage,                       IMAGE_BITMAP, 0, 0, LR_COPYRETURNORG);

hOldBitmap = SelectObject(hDC, hBitmap); :    :

// Delete hBitmap when you finish using it. DeleteObject (SelectObject (hDC, hOldBitmap));

STATUS
This behavior is by design.

Additional query words: unusable hDC Image Lists beta

Keywords : kbCtrl kbImgList kbOSWin2000 kbSDKWin32 kbGrpDSUser kbOSWin95

Issue type : kbprb

Technology : kbWin32SDKSearch kbAudDeveloper kbSDKSearch kbWin32sSearch