BUG: Incorrect Coordinates Passed to OLEDragDrop/OLEDragOver (200491)


The information in this article applies to:

  • The Microsoft Foundation Classes (MFC), when used with:
    • Microsoft Visual C++, 32-bit Editions 6.0
This article was previously published under Q200491

SYMPTOMS

When you use an ActiveX control, such as Microsoft TreeView control and Microsoft ListView control, from the COMCTL32.ocx file, (located in Visual C++ version 5.x), or the MSCOMCTL.ocx file (located in Visual C++ version 6.0) in a Microsoft Foundation Classes (MFC) application, then the x- and y-coordinates that are passed to the OLEDragDrop() and OLEDragOver() event handlers are incorrect. The passing of these incorrect handlers causes the control's HitTest() method to return a wrong value.

CAUSE

The control's HitTest() method needs and takes a Twips units and a positive y-coordinate value. However, the y-coordinate is a negative value when it is passed in to the MFC container's OLEDragDrop() and OLEDragOver() event handlers. In addition, the values passed in are measured in pixel units instead of Twips units.

RESOLUTION

Use the following code to perform the conversion from pixel units to Twips units in the OLEDragDrop/OLEDragOver event handlers: 

   void ConvertXYtoTwips(float FAR* x, float FAR* y)
   {
      // Get a device context.
      HDC hdc = GetDC(NULL);

      // Determine how many Twips are in one pixel.
      CPoint pOne(1, 1);
      SetMapMode(hdc, MM_TWIPS);
      DPtoLP(hdc, &pOne, 1);

      // Convert *x and *y to Twips units.
      float xx = *x * pOne.x;
      float yy = *y * pOne.y;//NOTE: both *y and pOne.y are negative values.

      // Release the device context.
      ReleaseDC(NULL, hdc);

      // X and y are in Twips pixel units.
      *x = xx;
      *y = yy;
   }

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

To better illustrate the usage of the ConvertXYtoTwips() function defined in the "Resolution" section, a Microsoft TreeView control (m_TreeView variable) is used in an AppWizard generated MFC Dialog-based container application (m_TestDlg). The following code shows how to highlight a node based on the mouse selection in the OLEDragDrop event handler, OnOLEDragDropTreectrl1(), of the dialog box: 

   BEGIN_EVENTSINK_MAP(CTestDlg, CDialog)
      //{{AFX_EVENTSINK_MAP(CTestDlg)
      ON_EVENT(CTestDlg, IDC_TREECTRL1, 1555 /* OLEDragDrop */,
         OnOLEDragDropTreectrl1,
         VTS_PDISPATCH VTS_PI4 VTS_PI2 VTS_PI2 VTS_PR4 VTS_PR4)
      //}}AFX_EVENTSINK_MAP
   END_EVENTSINK_MAP()
				

   void CTestDlg::OnOLEDragDropTreectrl1(
      LPDISPATCH FAR* Data, long FAR* Effect,
      short FAR* Button, short FAR* Shift, float FAR* x, float FAR* y)
   {
      // Convert x and y to Twips pixel units.
      ConvertXYtoTwips(x, y);

      // Determine which node should be highlighted in the
      // Microsoft TreeView control.
      CNode node = m_TreeView.HitTest(*x, *y);
      if (node)
      {
         VARIANT var;
         var.vt = VT_DISPATCH;
         var.pdispVal = node.m_lpDispatch;
         m_TreeView.SetDropHighlight(&var);
      }
   }


Steps to Reproduce Behavior

  1. Create an AppWizard dialog-based application with ActiveX Controls support. The dialog class is called CTestDlg.
  2. Insert a Microsoft TreeView control into the dialog resource.
  3. Use ClassWizard to associate the TreeView control with a member variable called m_TreeView. This association also causes Visual C++ to insert the C++ wrapper classes for the TreeView control into the project.
  4. Add some nodes to the TreeView control in response to the WM_INITDIALOG message of the CTestDlg dialog class. The following code sample illustrates this addition: 
       // The node becomes a child node of the node named it is connected to.
   #define tvwChild   (short) 4

   #include "node.h"     // for CNode class
   BOOL CTestDlg::OnInitDialog()
   {
      CDialog::OnInitDialog();

      // ...

      m_TreeView.SetOLEDropMode(1);

      CNodes nodes = m_TreeView.GetNodes();
      nodes.Clear();

      COleVariant NOPARAM( DISP_E_PARAMNOTFOUND, VT_ERROR );

      CNode node = nodes.Add(
         LPVARIANT(NOPARAM),                 // VARIANT* Relative
         LPVARIANT(NOPARAM),                 // VARIANT* Relationship
         LPVARIANT(COleVariant("R")),        // VARIANT* Key
         LPVARIANT(COleVariant("First")),    // VARIANT* Text
         LPVARIANT(NOPARAM),                 // VARIANT* Image
         LPVARIANT(NOPARAM));                // VARIANT* SelectedImage

      node = nodes.Add(
         LPVARIANT(COleVariant("R")),        // VARIANT* Relative
         LPVARIANT(COleVariant( tvwChild ) ),// VARIANT* Relationship
         LPVARIANT(COleVariant("C1")),       // VARIANT* Key
         LPVARIANT(COleVariant("Child 1")),  // VARIANT* Text
         LPVARIANT(NOPARAM),                 // VARIANT* Image
         LPVARIANT(NOPARAM));                // VARIANT* SelectedImage

      node = nodes.Add(
         LPVARIANT(COleVariant("R")),        // VARIANT* Relative
         LPVARIANT(COleVariant( tvwChild ) ),// VARIANT* Relationship
         LPVARIANT(COleVariant("C2")),       // VARIANT* Key
         LPVARIANT(COleVariant("Child 2")),  // VARIANT* Text
         LPVARIANT(NOPARAM),                 // VARIANT* Image
         LPVARIANT(NOPARAM));                // VARIANT* SelectedImage

      node = nodes.Add(
         LPVARIANT(NOPARAM),                 // VARIANT* Relative
         LPVARIANT(NOPARAM),                 // VARIANT* Relationship
         LPVARIANT(COleVariant("S")),        // VARIANT* Key
         LPVARIANT(COleVariant("Second")),   // VARIANT* Text
         LPVARIANT(NOPARAM),                 // VARIANT* Image
         LPVARIANT(NOPARAM));                // VARIANT* SelectedImage

      return TRUE;  // Return TRUE unless you set the focus to a control.
   }
  5. Use ClassWizard to add an OLEDragDrop event handler for the TreeView control. Add the code in OnOLEDragDropTreectrl1() without calling the ConvertXYtoTwips() function. The call to HitTest() returns NULL if the incorrect x and y values are used.
Modification Type:MajorLast Reviewed:10/24/2003
Keywords:kbbug kbCmnCtrls kbDragDrop kbpending KB200491
©2003 Microsoft Corporation. All rights reserved.