Class for drag-drop enabled TreeView

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I wrote a base class from which the MFC users can derive their TreeView
classes in a document-view based application instead of CTreeView. This
class adds to CtreeView build-in drag-and-drop support.

All that the developer have to do is to add this class to the AppWizard
generated project (with CTreeView as a View base class) and to replace the
base of the view class from CTreeView to CTreeViewExt. After that, he/she
has to overwrite the virtual functions of the base, which interface is self
explantory.

That’s all, the drag-and-drop tree view will be up and running !

Header file

#if !defined(AFX_TREEVIEWEXT_H__99D8F6F8_79F0_11D1_8DC6_0000E8125FE5__INCLUDED_)
#define AFX_TREEVIEWEXT_H__99D8F6F8_79F0_11D1_8DC6_0000E8125FE5__INCLUDED_

#if _MSC_VER >= 1000
#pragma once
#endif // _MSC_VER >= 1000
// TreeViewExt.h : header file
//

/////////////////////////////////////////////////////////////////////////////
// CTreeViewExt view

class CTreeViewExt : public CTreeView
{
protected:
	CTreeViewExt();           // protected constructor used by dynamic creation
	DECLARE_DYNCREATE(CTreeViewExt)

// Attributes
public:

// Operations
public:

// Overrides
	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CTreeViewExt)
	protected:
	virtual void OnDraw(CDC* pDC);      // overridden to draw this view
	//}}AFX_VIRTUAL

// Implementation
protected:
	HTREEITEM m_hDraggedItem;
	BOOL m_bDraggingNow;
	CImageList *m_pDragImageList;
	virtual ~CTreeViewExt();
#ifdef _DEBUG
	virtual void AssertValid() const;
	virtual void Dump(CDumpContext& dc) const;
#endif

	// Generated message map functions
protected:
	virtual void CopyItemProperties(HTREEITEM hNewItem, HTREEITEM hDraggedItem);
	virtual BOOL IsItemCanBeDroppedOn(HTREEITEM hSource, HTREEITEM hTarget);
	virtual BOOL ItemCanBeDragged(HTREEITEM hItem);
	//{{AFX_MSG(CTreeViewExt)
	afx_msg void OnBegindrag(NMHDR* pNMHDR, LRESULT* pResult);
	afx_msg void OnMouseMove(UINT nFlags, CPoint point);
	afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
	//}}AFX_MSG
	DECLARE_MESSAGE_MAP()
};

/////////////////////////////////////////////////////////////////////////////

//{{AFX_INSERT_LOCATION}}
// Microsoft Developer Studio will insert additional declarations immediately before the previous line.

#endif // !defined(AFX_TREEVIEWEXT_H__99D8F6F8_79F0_11D1_8DC6_0000E8125FE5__INCLUDED_)

Implementation file

// TreeViewExt.cpp : implementation file
//

#include "stdafx.h"
#include "TreeViewExt.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CTreeViewExt

IMPLEMENT_DYNCREATE(CTreeViewExt, CTreeView)

CTreeViewExt::CTreeViewExt()
{
	m_bDraggingNow		= FALSE;
	m_hDraggedItem		= NULL;
	m_pDragImageList	= NULL;
}

CTreeViewExt::~CTreeViewExt()
{
}


BEGIN_MESSAGE_MAP(CTreeViewExt, CTreeView)
	//{{AFX_MSG_MAP(CTreeViewExt)
	ON_NOTIFY_REFLECT(TVN_BEGINDRAG, OnBegindrag)
	ON_WM_MOUSEMOVE()
	ON_WM_LBUTTONUP()
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CTreeViewExt drawing

void CTreeViewExt::OnDraw(CDC* pDC)
{
	CDocument* pDoc = GetDocument();
	// TODO: add draw code here
}

/////////////////////////////////////////////////////////////////////////////
// CTreeViewExt diagnostics

#ifdef _DEBUG
void CTreeViewExt::AssertValid() const
{
	CTreeView::AssertValid();
}

void CTreeViewExt::Dump(CDumpContext& dc) const
{
	CTreeView::Dump(dc);
}
#endif //_DEBUG

/////////////////////////////////////////////////////////////////////////////
// CTreeViewExt message handlers

void CTreeViewExt::OnBegindrag(NMHDR* pNMHDR, LRESULT* pResult)
{
	NM_TREEVIEW* pNMTreeView = (NM_TREEVIEW*)pNMHDR;

	if (!m_bDraggingNow)
	{
		if (ItemCanBeDragged(pNMTreeView->itemNew.hItem))
		{
			CTreeCtrl& tree = GetTreeCtrl();
			tree.SetCapture();
			m_bDraggingNow = TRUE;
			m_hDraggedItem = pNMTreeView->itemNew.hItem;
			tree.Select(m_hDraggedItem, TVGN_CARET);
			m_pDragImageList = tree.CreateDragImage(m_hDraggedItem);
			m_pDragImageList->DragEnter(&tree, pNMTreeView->ptDrag);
			m_pDragImageList->BeginDrag(0, CPoint(0, 0));
		}
	}

	*pResult = 0;
}

void CTreeViewExt::OnMouseMove(UINT nFlags, CPoint point)
{
	if (m_bDraggingNow)
	{
		CTreeCtrl& tree = GetTreeCtrl();
		m_pDragImageList->DragEnter(&tree, point);
		m_pDragImageList->DragMove(point);
	}

	CTreeView::OnMouseMove(nFlags, point);
}

void CTreeViewExt::OnLButtonUp(UINT nFlags, CPoint point)
{
	if (m_bDraggingNow)
	{
		ReleaseCapture();

		m_bDraggingNow = FALSE;
		m_pDragImageList->EndDrag();
		delete m_pDragImageList;
		m_pDragImageList = NULL;

		CTreeCtrl& tree = GetTreeCtrl();
		UINT flags;
		HTREEITEM hTargetItem = tree.HitTest(point, &flags);
		if (hTargetItem != NULL && IsItemCanBeDroppedOn(m_hDraggedItem, hTargetItem))
		{
			HTREEITEM hNewItem = tree.InsertItem("Untitled", hTargetItem);
			CopyItemProperties(hNewItem, m_hDraggedItem);
			if (nFlags != MK_CONTROL)
				tree.DeleteItem(m_hDraggedItem);
		}

		m_hDraggedItem = NULL;
	}

	CTreeView::OnLButtonUp(nFlags, point);
}

BOOL CTreeViewExt::ItemCanBeDragged(HTREEITEM hItem)
{
	return FALSE;
}

BOOL CTreeViewExt::IsItemCanBeDroppedOn(HTREEITEM hSource, HTREEITEM hTarget)
{
	return FALSE;
}

void CTreeViewExt::CopyItemProperties(HTREEITEM hNewItem, HTREEITEM hDraggedItem)
{

}