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MultiSelect DragImage in CTreeCtrl

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21 Dec 2004CPOL1 min read 95.2K   4.9K   49   4
This article describes how to create a multiselect drag image in CTreeCtrl.

Sample screenshot

Introduction

This article describes how to create a multi select drag image in CTreeCtrl. I have created a custom tree control CDragDropTreeCtrl (derived from CTreeCtrl) for adding drag and drop support. CreateDragImageEx() is the core function, it creates the drag image list.

CDragDropTreeCtrl

This class implements multiple selection with mouse, with the Ctrl or Shift key down. The DragDetect() API is used to detect the start of drag. Once the dragging is detected, the OnDrag() function is invoked. The OnDrag() function invokes CreateImageEx() to create the drag image list. The rest is the same as single selection drag. BeginDrag() and DragEnter() functions are used to prepare the image list for dragging. In the mouse move event, the drag image is moved.

CreateDragImageEx

This is the core function, which creates the drag image list. Steps in creating drag image list are:

  1. Get the image list associated with the tree control
  2. Get the icon size with the help of the API ImageList_GetIconSize()
  3. Calculate the bounding rect of the drag image
    1. Calculate the maximum width
    2. Calculate the height of single item and multiply it with list size to get the total height
  4. Create a memory device context
  5. Prepare the memory DC
  6. Create and prepare bitmap object
  7. Select Bitmap into the memory DC
  8. For each element in the list, extract the icon and associated text and draw them to the memory DC
  9. Create a new image list
  10. Add the bitmap to the image list
C++
// 1.Get the image list associated with the tree control
   CImageList *pImageList = GetImageList(TVSIL_NORMAL); 
// 2.Get the icon size with the help of the API ImageList_GetIconSize()
    int cx,cy;
    ImageList_GetIconSize(*pImageList, &cx, &cy); 
// 3.Calculate the bounding rect of the drag image
// a) Calculate the maximum width    
 
 for ( nIdx = 0; nIdx < nNumSelected; nIdx++) 
 {
   // Get the item's height and width one by one
   hItem = m_vSelItem[nIdx];
   strItemText = GetItemText(hItem);
   rectFirstItem.SetRectEmpty();
   pDragImageCalcDC->DrawText(strItemText, rectFirstItem, DT_CALCRECT);
   if(nMaxWidth < ( rectFirstItem.Width()+cx))
    nMaxWidth = rectFirstItem.Width()+cx;
 }
C++
// b) Calculate the height of single item and multiply it
// with list size to get the total height
    hItem = m_vSelItem[0];
    strItemText = GetItemText(hItem);
    rectFirstItem.SetRectEmpty();
    pDragImageCalcDC->DrawText(strItemText, rectFirstItem, DT_CALCRECT);
    
    rectTextArea.SetRect(1, 1, nMaxWidth, rectFirstItem.Height());
    rectBounding.SetRect(0,0, nMaxWidth+2, 
                 (rectFirstItem.Height()+2)*nNumSelected);
    
// 4.Create a memory device context
   CDC MemoryDC;
// 5.Prepare the memory DC
  if(!MemoryDC.CreateCompatibleDC(&DraggedNodeDC))
    return NULL;
// 6.Create and prepare bitmap object
  CBitmap   DraggedNodeBmp;
  if(!DraggedNodeBmp.CreateCompatibleBitmap(&DraggedNodeDC, 
              rectBounding.Width(), rectBounding.Height()))
    return NULL;
// 7.Select Bitmap into the memory DC
  pBitmapOldMemDCBitmap = MemoryDC.SelectObject( &DraggedNodeBmp );
// 8.For each element in the list extract the icon
// and associated text and draw them to the memory DC
C++
for( nIdx = 0; nIdx < nNumSelected; nIdx++)
{
  hItem = m_vSelItem[nIdx];
  int nImg = 0,nSelImg=0;
  GetItemImage(hItem,nImg,nSelImg);
  HICON hIcon = pImageList->ExtractIcon(nImg);
  //cdcMemory.DrawIcon(rectTextArea.left,rectTextArea.top,hIcon);
  MemoryDC.MoveTo(rectTextArea.left,rectTextArea.top);
  if( nIdx != nNumSelected-1 )
  {
    MemoryDC.LineTo(rectTextArea.left,rectTextArea.top+18);
  }
  else
  {
    MemoryDC.LineTo(rectTextArea.left,rectTextArea.top+8);
  }
  MemoryDC.MoveTo(rectTextArea.left,rectTextArea.top+8);
  MemoryDC.LineTo(rectTextArea.left+5,rectTextArea.top+8);
C++
   int nLeft = rectTextArea.left;
   rectTextArea.left += 3;
   ::DrawIconEx(MemoryDC.m_hDC,rectTextArea.left,rectTextArea.top,hIcon,
                16,16,0,NULL,DI_NORMAL);
   rectTextArea.left += cx;
   MemoryDC.Rectangle(rectTextArea);
   MemoryDC.DrawText(GetItemText(hItem), rectTextArea,
                  DT_LEFT| DT_SINGLELINE|DT_NOPREFIX);
   rectTextArea.left = nLeft;
   rectTextArea.OffsetRect(0, rectFirstItem.Height()+2);
   DestroyIcon(hIcon);
 }

// 9.Create a new image list
  pImageListDraggedNode = new CImageList;
  pImageListDraggedNode->Create(rectBounding.Width(), rectBounding.Height(),
                                ILC_COLOR | ILC_MASK, 0, 1);
// 10.Add the bitmap to the image list
   pImageListDraggedNode->Add(&DraggedNodeBmp, RGB(255, 255,255));

Conclusion

This CDragDropTreeCtrl implements multiple selection with mouse only. The keyboard support will be updated later. With this method for creating drag image list, we can create drag image for list controls also.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
India India
A senior engineer who likes reading and coding Smile | :) . I can be reached at sudheeshps@gmail.com

Comments and Discussions

 
QuestionWhy the root node is always selected? Pin
oleg6326-May-23 6:25
professionaloleg6326-May-23 6:25 
GeneralMy vote of 5 Pin
yu-jian24-Sep-12 14:52
yu-jian24-Sep-12 14:52 
GeneralI am in china.My English is poor,but I need you help urgently. Pin
Plainzeng29-Mar-07 16:15
Plainzeng29-Mar-07 16:15 
GeneralFantastic contribution :) [modified] Pin
Setesh826-Mar-07 10:43
Setesh826-Mar-07 10:43 
I thank you for this control it was pretty much what I wanted.

I only have one issue. The first item inserted at the root is always selected. This is causing issues with other areas of my code.

Would you happen to know how to correct this problem or perhaps where to start looking?


-- modified at 17:24 Tuesday 6th March, 2007

I just found that the problem goes away if I call CTreeCtrl::OnLButtonDown() in the derived OnLButtonDown. However this causes another issue. You now have to double click to expand the child items of the tree.

I would appreciate any assistance.

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