Drag and drop

Step 0: Make sure that the control style supports drag and drop

Step 1: Declare member variables

protected:
	CImageList*	m_pDragImage;
	BOOL		m_bLDragging;
	HTREEITEM	m_hitemDrag,m_hitemDrop;

Step 2: Add handler for TVN_BEGINDRAG

BeginDrag() function is called with an argument of zero and a point. The zero indicates the first image, which is the only image in the image list. The value we use for the second argument causes the image to be drawn to the right lower side of the cursor. You may want to experiment with this value if the image position does not suit your taste.

We call the DragEnter() to display the drag image. The first argument is NULL so that the drag image will be visible even if the mouse is dragged outside the treeview control.
 

void CTreeCtrlX::OnBeginDrag(NMHDR* pNMHDR, LRESULT* pResult) 
{
	NM_TREEVIEW* pNMTreeView = (NM_TREEVIEW*)pNMHDR;
	*pResult = 0;

	m_hitemDrag = pNMTreeView->itemNew.hItem;
	m_hitemDrop = NULL;

	m_pDragImage = CreateDragImage(m_hitemDrag);  // get the image list for dragging
	// CreateDragImage() returns NULL if no image list
	// associated with the tree view control
	if( !m_pDragImage )
		return;

	m_bLDragging = TRUE;
	m_pDragImage->BeginDrag(0, CPoint(-15,-15));
	POINT pt = pNMTreeView->ptDrag;
	ClientToScreen( &pt );
	m_pDragImage->DragEnter(NULL, pt);
	SetCapture();
}

Step 3: Add handler for WM_MOUSEMOVE to update drag image

void CTreeCtrlX::OnMouseMove(UINT nFlags, CPoint point) 
{
	HTREEITEM	hitem;
	UINT		flags;

	if (m_bLDragging)
	{
		POINT pt = point;
		ClientToScreen( &pt );
		CImageList::DragMove(pt);
		if ((hitem = HitTest(point, &flags)) != NULL)
		{
			CImageList::DragShowNolock(FALSE);
			SelectDropTarget(hitem);
			m_hitemDrop = hitem;
			CImageList::DragShowNolock(TRUE);
		}
	}
	
	CTreeCtrl::OnMouseMove(nFlags, point);
}

Step 4: Finally add handler for WM_LBUTTONUP

void CTreeCtrlX::OnLButtonUp(UINT nFlags, CPoint point) 
{
	CTreeCtrl::OnLButtonUp(nFlags, point);

	if (m_bLDragging)
	{
		m_bLDragging = FALSE;
		CImageList::DragLeave(this);
		CImageList::EndDrag();
		ReleaseCapture();

		delete m_pDragImage;

		// Remove drop target highlighting
		SelectDropTarget(NULL);

		if( m_hitemDrag == m_hitemDrop )
			return;

		// If Drag item is an ancestor of Drop item then return
		HTREEITEM htiParent = m_hitemDrop;
		while( (htiParent = GetParentItem( htiParent )) != NULL )
		{
			if( htiParent == m_hitemDrag ) return;
		}

		Expand( m_hitemDrop, TVE_EXPAND ) ;

		HTREEITEM htiNew = CopyBranch( m_hitemDrag, m_hitemDrop, TVI_LAST );
		DeleteItem(m_hitemDrag);
		SelectItem( htiNew );
	}

}