Q200491: BUG: Incorrect Coordinates Passed to OLEDragDrop/OLEDragOver
Article: Q200491
Product(s): Microsoft C Compiler
Version(s): 6.0
Operating System(s):
Keyword(s): kbCmnCtrls kbDragDrop kbMFC kbGrpDSMFCATL
Last Modified: 27-MAR-2001
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The information in this article applies to:
- The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++, 32-bit Editions, version 6.0
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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.
Additional query words: ocx
======================================================================
Keywords : kbCmnCtrls kbDragDrop kbMFC kbGrpDSMFCATL
Technology : kbAudDeveloper kbMFC
Version : :6.0
Issue type : kbbug
Solution Type : kbpending
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