This section describes, via sample code fragments, how you can use the error handling methods. Specifically the first sample code shows how wpQueryError retrieves the error identity that was set on an object. The second code fragment shows how to design your own error handling system by overriding wpSetError.

The following sample code shows how wpQueryError retrieves the error identity that was set on an object:

// METHOD: my_wpDrop
//
// DESCRIPTION:
//   SOMObject
//     ÀÄÄÄWPObject
//           ÀÄÄÄWPFileSystem
//                ÀÄÄÄWPFolder
//                       ÀÄÄÄMyFolder
//
//   When an object is dropped on a folder,
//   this method is called on the target folder.
//
//   This sample code shows how wpQueryError retrieves
//   the error identity that was set on an object.
//
SOM_Scope MRESULT SOMLINK my_wpDrop(MyFolder *self,
                                    HWND      hwndCnr,
                                    PDRAGINFO pDragInfo,
                                    PDRAGITEM pDragItem)
{
  MRESULT       mr;        // Return value
  ULONG         ulError;   // Error code set on folder

  // Clear existing error code
  _wpSetError(self, NO_ERROR);
  // Call the parent to handle the drop
  mr = parent_wpDrop(self, hwndCnr, pDragInfo, pDragItem);

  // If parent returns an error, check to see if the disk is full
  if (mr == (MRESULT)RC_DROP_ERROR)
  {
    // Query the error code set on the folder
    ulError = _wpQueryError(self);
    // If the disk is full, display a message to the user
    if (ulError == ERROR_DISK_FULL)
    {
      WinMessageBox(HWND_DESKTOP,
                    NULLHANDLE,             // Owner Window
                    "Error Disk Full",      // Body of the message
                    "Unsuccessful Drop",    // Title of the message
                    0,                      // Message box id
                    MB_ERROR | MB_OK);      // Icon and button flags
    }
  }
  return mr;
}

The following sample code shows shows how to design your own error handling system by overriding wpSetError:

// METHOD: my_wpSetError
//
// DESCRIPTION:
//   Sets the error on an object.
//   User-defined errors can be handled here.
//
//   This sample code shows how to design your own
//   error handling system by overriding wpSetError.

SOM_Scope BOOL SOMLINK my_wpSetError(MyFolder *self,
                                     ULONG ulErrorId)
{
  // Check to see if this is a user-defined error
  if (ulErrorId > WPERR_USER)
  {
    // Handle user-defined errors here
  }
  // Call the parent to set the error
  return (parent_wpSetError(self, ulErrorId));
}