Drag and Drop Listbox Items using OLE

// OLEDragAndDropListBox.cpp : implementation file
//

#include "stdafx.h"
#include "OLEDragAndDropListBox.h"
#include ".\oledraganddroplistbox.h"

#define TID_SCROLLDOWN  100
#define TID_SCROLLUP    101

// COLEDragAndDropListBox

IMPLEMENT_DYNAMIC(COLEDragAndDropListBox, CListBox)
COLEDragAndDropListBox::COLEDragAndDropListBox()
: m_DraggedIndex(-1)
, m_DropIndex(-1)
, m_Interval(0)
, m_CanIntenalDrop(TRUE)
{
}

COLEDragAndDropListBox::~COLEDragAndDropListBox()
{
}


BEGIN_MESSAGE_MAP(COLEDragAndDropListBox, CListBox)
   ON_WM_LBUTTONDOWN()
   ON_WM_MOUSEMOVE()
   ON_WM_LBUTTONUP()
   ON_WM_TIMER()
END_MESSAGE_MAP()

// COLEDragAndDropListBox message handlers

void COLEDragAndDropListBox::PreSubclassWindow()
{
   __super::PreSubclassWindow();
   VERIFY(Register(this) == TRUE);
   //register our own Clipboard format
   m_cfFormat = RegisterClipboardFormat("{2FCA1C31-D8F1-4f20-8051-B0CCF7B6FD0D}");
}

void COLEDragAndDropListBox::OnLButtonDown(UINT nFlags, CPoint point)
{
   __super::OnLButtonDown(nFlags, point);

   //keep track of the item that was clicked on
   //WM_MOUSEMOVE message is going to use that to 
   //create the COleDataSource
   m_Interval = 0;
   m_DropIndex = LB_ERR;
   m_DraggedIndex = LB_ERR;
   BOOL Outside;
   int Index = ItemFromPoint(point,Outside);
   if (Index != LB_ERR && !Outside)
   {
      m_DraggedIndex = Index;
      SetCurSel(Index);
   }
}

void COLEDragAndDropListBox::OnMouseMove(UINT nFlags, CPoint point)
{
   if (m_DraggedIndex != LB_ERR && (nFlags & MK_LBUTTON))
   {
      //create the COleDataSource, and attach the data to it
      COleDataSource DataSource;
      HGLOBAL hData = GetData(m_DraggedIndex);
      if (hData)
      {
         DataSource.CacheGlobalData(m_cfFormat,hData);

         //allow the user to drag it.
         DROPEFFECT DropEffect = DataSource.DoDragDrop(GetDragItemEffects(m_DraggedIndex));
         //if the user wanted to move the item then delete it
         //Only do this if it was dragged to another window
         //OnDrop handles deleting a moved item within the same window
         if (DropEffect & DROPEFFECT_MOVE && m_DraggedIndex != LB_ERR)
         {
            RemoveItem(m_DraggedIndex);
         }
         m_DraggedIndex = LB_ERR;
         GetParent()->SendMessage(WM_COMMAND,MAKEWPARAM(GetDlgCtrlID(),LBN_SELCHANGE),(LPARAM)CListBox::m_hWnd);
      }
   }

   __super::OnMouseMove(nFlags, point);
}

void COLEDragAndDropListBox::OnLButtonUp(UINT nFlags, CPoint point)
{
   //cancel everything
   KillTimer(TID_SCROLLDOWN);
   KillTimer(TID_SCROLLUP);
   m_Interval = 0;
   m_DropIndex = LB_ERR;
   Invalidate();

   __super::OnLButtonUp(nFlags, point);
}

DROPEFFECT COLEDragAndDropListBox::OnDragEnter(CWnd* pWnd,COleDataObject* pDataObject,DWORD dwKeyState,CPoint point)
{
   if (DragOriginateInSameWindow() && !GetCanInternalDrop())
   {
      return DROPEFFECT_NONE;
   }
   //if the data is the kind we want
   if (pDataObject->IsDataAvailable(m_cfFormat))
   {
      //bring window to top
      ActivateWindow();
      //draw the line where it would be inserted
      DrawTheLines(GetItemAt(point));
      //scroll if needed
      DoTheScrolling(point);
      //return how the user can drop the item
      return GetDropItemEffects(pDataObject,dwKeyState);
   }
   return DROPEFFECT_NONE;
}

DROPEFFECT COLEDragAndDropListBox::OnDragOver(CWnd* pWnd,COleDataObject* pDataObject,DWORD dwKeyState,CPoint point)
{
   if (DragOriginateInSameWindow() && !GetCanInternalDrop())
   {
      return DROPEFFECT_NONE;
   }
   //if the data is the kind we want
   if (pDataObject->IsDataAvailable(m_cfFormat))
   {
      //draw the line where it would be inserted
      DrawTheLines(GetItemAt(point));
      //scroll if needed
      DoTheScrolling(point);
      //return how the user can drop the item
      return GetDropItemEffects(pDataObject,dwKeyState);
   }
   return DROPEFFECT_NONE;
}



void COLEDragAndDropListBox::OnDragLeave(CWnd* pWnd)
{
   //cancel everything
   KillTimer(TID_SCROLLDOWN);
   KillTimer(TID_SCROLLUP);
   //Clear The line that was drawn
   CDC *pDC = GetDC(); 
   ClearOldLine(pDC,m_DropIndex);
   ReleaseDC(pDC);
   m_Interval = 0;
   m_DropIndex = LB_ERR;
}

BOOL COLEDragAndDropListBox::OnDrop(CWnd* pWnd,COleDataObject* pDataObject,DROPEFFECT dropEffect,CPoint point)
{
   BOOL Ret = FALSE;
   if (DragOriginateInSameWindow() && !GetCanInternalDrop())
   {
      return FALSE;
   }
   //if it is a format that we handle
   if (pDataObject->IsDataAvailable(m_cfFormat))
   {
      //get the index of where the user want's to insert item
      int Index = GetItemAt(point);
      HGLOBAL hGlobal = pDataObject->GetGlobalData(m_cfFormat);

      //if the Drag was initiated in the same window as the drop and
      //user wants to move the item then we have to handle the delete here
      //because if the original item was at a higher index than the dropped index
      //we would have to delete the dragged item first before we
      //insert the new item
      if (DragOriginateInSameWindow() && dropEffect == DROPEFFECT_MOVE)
      {
         if (m_DraggedIndex < Index)
         {
            Ret = DroppedAt(Index,hGlobal);
            RemoveItem(m_DraggedIndex);
            m_DraggedIndex = LB_ERR;
            SetCurSel(Index-1);
         }
         else if (m_DraggedIndex > Index)
         {
            RemoveItem(m_DraggedIndex);
            m_DraggedIndex = LB_ERR;
            Ret = DroppedAt(Index,hGlobal);
         }
      }
      else //simply drop the item in the desired index
      {
         Ret = DroppedAt(Index,hGlobal);
         GetParent()->SendMessage(WM_COMMAND,MAKEWPARAM(GetDlgCtrlID(),LBN_SELCHANGE),(LPARAM)CListBox::m_hWnd);
      }
   }
   m_DropIndex = LB_ERR;
   return Ret;
}


BOOL COLEDragAndDropListBox::DragOriginateInSameWindow()
{
   //if m_DraggedIndex is equal to LB_ERR then the dragging
   //did not originate in this window
   return m_DraggedIndex != LB_ERR;
}

//find the item under the point, 
//returns -1 if it is passed the last item in the list
int COLEDragAndDropListBox::GetItemAt(CPoint Point)
{
   BOOL Outside;
   int Index = ItemFromPoint(Point,Outside);
   if (Outside)
   {
      Index = -1;
   }
   return Index;
}

void COLEDragAndDropListBox::DrawTheLines(int Index)
{
   CRect ClientRect;
   GetClientRect(&ClientRect);

   CDC *pDC = GetDC();

   ClearOldLine(pDC,m_DropIndex);

   m_DropIndex = Index;

   DrawNewLine(pDC,m_DropIndex);

   ReleaseDC(pDC);
}

void COLEDragAndDropListBox::ClearOldLine(CDC *pDC,int Index)
{
   CRect ClientRect;
   GetClientRect(&ClientRect);

   CRect Rect;
   int Width = 2;
   CPen Pen(PS_SOLID,Width,RGB(255,255,255));
   CPen *pOldPen = pDC->SelectObject(&Pen);
   if (Index != LB_ERR)
   {
      GetItemRect(m_DropIndex,&Rect);
      if (ClientRect.PtInRect(Rect.TopLeft()))
      {
         pDC->MoveTo(Rect.left,Rect.top+1);
         pDC->LineTo(Rect.right-(Width/2),Rect.top+1);
      }
   }
   else
   {
      GetItemRect(GetCount()-1,&Rect);
      if (ClientRect.PtInRect(CPoint(0,Rect.bottom)))
      {
         pDC->MoveTo(Rect.left,Rect.bottom);
         pDC->LineTo(Rect.right-(Width/2),Rect.bottom);
      }
   }
   pDC->SelectObject(pOldPen);
}

void COLEDragAndDropListBox::DrawNewLine(CDC *pDC,int Index)
{
   CRect ClientRect;
   GetClientRect(&ClientRect);

   int Width = 2;

   CRect Rect;
   CPen Pen(PS_SOLID,Width,RGB(0,0,0));
   CPen *pOldPen = pDC->SelectObject(&Pen);
   if (Index != LB_ERR)
   {
      GetItemRect(Index,&Rect);
      if (ClientRect.PtInRect(Rect.TopLeft()))
      {
         pDC->MoveTo(Rect.left,Rect.top+1);
         pDC->LineTo(Rect.right-(Width/2),Rect.top+1);
      }
   }
   else
   {
      GetItemRect(GetCount()-1,&Rect);
      if (ClientRect.PtInRect(CPoint(0,Rect.bottom)))
      {
         pDC->MoveTo(Rect.left,Rect.bottom);
         pDC->LineTo(Rect.right-(Width/2),Rect.bottom);
      }
   }
   pDC->SelectObject(pOldPen);
}

void COLEDragAndDropListBox::DoTheScrolling(CPoint Point)
{
   CRect ClientRect;
   GetClientRect(&ClientRect);
   if (Point.y > ClientRect.Height()-10)
   {
      DWORD Interval = 250 / (1+ ((Point.y-ClientRect.Height())/GetItemHeight(0)));
      if (Interval != m_Interval)
      {
         m_Interval = Interval;
         SetTimer(TID_SCROLLDOWN,Interval,NULL);
         OnTimer(TID_SCROLLDOWN);
      }
   }
   else if (Point.y < 10)
   {
      DWORD Interval = 250 / (1+(abs(Point.y)/GetItemHeight(1)));
      if (Interval != m_Interval)
      {
         m_Interval = Interval;
         SetTimer(TID_SCROLLUP,Interval,NULL);
         OnTimer(TID_SCROLLUP);
      }
   }
   else
   {
      KillTimer(TID_SCROLLDOWN);
      KillTimer(TID_SCROLLUP);
      m_Interval = 0;
   }
}

void COLEDragAndDropListBox::OnTimer(UINT nIDEvent)
{
   if (nIDEvent == TID_SCROLLDOWN)
   {
      if (m_DropIndex != -1)
      {
         DrawTheLines(m_DropIndex+1);
         SetTopIndex(GetTopIndex()+1);
      }
      else
      {
         KillTimer(nIDEvent);
         m_Interval = 0;
      }
   }
   else if (nIDEvent == TID_SCROLLUP)
   {
      if (GetTopIndex() != 0)
      {
         DrawTheLines(m_DropIndex-1);
         SetTopIndex(GetTopIndex()-1);
      }
      else
      {
         KillTimer(nIDEvent);
         m_Interval = 0;
      }
   }

   __super::OnTimer(nIDEvent);
}


HGLOBAL COLEDragAndDropListBox::GetData(int ForIndex)
{
   CString Text;
   GetText(ForIndex,Text);
   HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE,Text.GetLength()+1);
   char *pChar = (char *)GlobalLock(hGlobal);
   strcpy(pChar,Text);
   GlobalUnlock(hGlobal);
   return hGlobal;
}

BOOL COLEDragAndDropListBox::DroppedAt(int InsertBefore,HGLOBAL hGlobal)
{
   char * pChar = (char *)GlobalLock(hGlobal);
   int Index = InsertString(InsertBefore,pChar);
   SetCurSel(Index);
   GlobalUnlock(hGlobal);
   
   return TRUE;
}

DROPEFFECT COLEDragAndDropListBox::GetDropItemEffects(COleDataObject* /*pDataObject*/,DWORD dwKeyState)
{
   if (DragOriginateInSameWindow())
   {
      if (dwKeyState & MK_CONTROL)
      {
         return DROPEFFECT_COPY;
      }
      return DROPEFFECT_MOVE;
   }

   if (dwKeyState & MK_SHIFT)
   {
      return DROPEFFECT_MOVE;
   }
   return DROPEFFECT_COPY;
}

DROPEFFECT COLEDragAndDropListBox::GetDragItemEffects(int Index)
{
   return DROPEFFECT_COPY|DROPEFFECT_MOVE;
}

void COLEDragAndDropListBox::RemoveItem(int Index)
{
   DeleteString(Index);
}

void COLEDragAndDropListBox::ActivateWindow()
{
   CWnd *pWnd = GetParent();
   if (pWnd)
   {
      pWnd->SetForegroundWindow();
      pWnd->BringWindowToTop();
      pWnd->SetActiveWindow();
   }
}