在MFC开发中，CTreeCtrl控件用于展示树形结构数据。本文探讨如何将CTreeCtrl的树形结构存储到SQLite数据库，并在需要时重新构建树形结构。

树节点的位置通过父节点（hParent）和插入顺序（hInsertAfter）确定。这种设计使得节点的增删改操作仅需更新少量数据即可实现。为了便于存储和恢复，我们使用节点的层级（lev）和遍历序号（idno），配合唯一标识符（id）来记录树结构。

节点的id是自动增长的整数，在数据库中确保唯一性。保存树结构时，计算每个节点的lev和idno值并存入数据库；恢复树结构时，利用这些值重新构造树形结构。

关键代码实现

头文件定义

#pragma once

#include "ViewTree.h"
#include "CSQLite.h"

class CFileViewToolBar : public CMFCToolBar
{
    virtual void OnUpdateCmdUI(CFrameWnd* /*pTarget*/, BOOL bDisableIfNoHndler)
    {
        CMFCToolBar::OnUpdateCmdUI((CFrameWnd*) GetOwner(), bDisableIfNoHndler);
    }

    virtual BOOL AllowShowOnList() const { return FALSE; }
};

class CFileView : public CDockablePane
{
public:
    CFileView();
    ~CFileView();

    void AdjustLayout();
    void OnChangeVisualStyle();

    CSQLite m_SQLite;
    HTREEITEM m_hNodeSrc;
    HTREEITEM m_hNodeFile;

    struct FileTable
    {
        int id;
        int lev;
        int idno;
        char name[256];
        HTREEITEM hItem;
    };

    FileTable* m_pFileTable;

    int m_NodeIndex;
    int m_NodeLevel;

    void TraverseAndSave(HTREEITEM hItem, CString& sql);
    void TraverseAndUpdate(HTREEITEM hItem, CString& sql);
    void RestoreTreeFromDB();
    void InsertTreeNode(HTREEITEM hParent, FileTable& data);

protected:
    CViewTree m_wndFileView;
    CImageList m_FileViewImages;
    CFileViewToolBar m_wndToolBar;

    void FillFileView();

BEGIN_MESSAGE_MAP(CFileView, CDockablePane)
    ON_WM_CREATE()
    ON_WM_SIZE()
    ON_WM_CONTEXTMENU()
    ON_COMMAND(ID_POP_EXP_SAVE, &CFileView::OnPopExpSave)
    ON_COMMAND(ID_POP_EXP_UPDATE, &CFileView::OnPopExpUpdate)
END_MESSAGE_MAP()

public:
    afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct);
    afx_msg void OnSize(UINT nType, int cx, int cy);
    afx_msg void OnContextMenu(CWnd* pWnd, CPoint point);
};

CPP文件实现

#include "stdafx.h"
#include "mainfrm.h"
#include "FileView.h"

CFileView::CFileView()
{
    m_pFileTable = nullptr;
}

CFileView::~CFileView()
{
    if (m_pFileTable != nullptr)
    {
        delete[] m_pFileTable;
        m_pFileTable = nullptr;
    }
}

void CFileView::TraverseAndSave(HTREEITEM hItem, CString& sql)
{
    if (!hItem) return;

    FileTable* pData = (FileTable*)m_wndFileView.GetItemData(hItem);
    CString itemText = m_wndFileView.GetItemText(hItem);

    CString insertSql;
    insertSql.Format(_T("INSERT INTO tree_data(id, level, index, name) VALUES(%d, %d, %d, '%s');"),
                     pData->id, m_NodeLevel, m_NodeIndex++, itemText);

    sql += insertSql;

    HTREEITEM hChild = m_wndFileView.GetChildItem(hItem);
    if (hChild)
    {
        m_NodeLevel++;
        TraverseAndSave(hChild, sql);
        m_NodeLevel--;
    }

    HTREEITEM hSibling = m_wndFileView.GetNextSiblingItem(hItem);
    if (hSibling)
    {
        TraverseAndSave(hSibling, sql);
    }
}

void CFileView::TraverseAndUpdate(HTREEITEM hItem, CString& sql)
{
    if (!hItem) return;

    FileTable* pData = (FileTable*)m_wndFileView.GetItemData(hItem);
    CString itemText = m_wndFileView.GetItemText(hItem);

    CString updateSql;
    updateSql.Format(_T("UPDATE tree_data SET level=%d, index=%d, name='%s' WHERE id=%d;"),
                     m_NodeLevel, m_NodeIndex++, itemText, pData->id);

    sql += updateSql;

    HTREEITEM hChild = m_wndFileView.GetChildItem(hItem);
    if (hChild)
    {
        m_NodeLevel++;
        TraverseAndUpdate(hChild, sql);
        m_NodeLevel--;
    }

    HTREEITEM hSibling = m_wndFileView.GetNextSiblingItem(hItem);
    if (hSibling)
    {
        TraverseAndUpdate(hSibling, sql);
    }
}

void CFileView::RestoreTreeFromDB()
{
    CString query = _T("SELECT id, level, index, name FROM tree_data ORDER BY index;");
    int rows, cols;
    if (!m_SQLite.Query(query, rows, cols)) return;

    m_pFileTable = new FileTable[rows];

    for (int i = 0; i < rows; ++i)
    {
        m_pFileTable[i].id = atoi(m_SQLite.m_sresult[i * cols + 0]);
        m_pFileTable[i].lev = atoi(m_SQLite.m_sresult[i * cols + 1]);
        m_pFileTable[i].idno = atoi(m_SQLite.m_sresult[i * cols + 2]);
        strcpy_s(m_pFileTable[i].name, m_SQLite.m_sresult[i * cols + 3]);
    }

    HTREEITEM hRoot = nullptr;
    for (int i = 0; i < rows; ++i)
    {
        FileTable& data = m_pFileTable[i];
        HTREEITEM hParent = (data.lev == 0) ? TVI_ROOT : m_pFileTable[data.lev - 1].hItem;
        HTREEITEM newItem = m_wndFileView.InsertItem(data.name, hParent, TVI_LAST);
        m_wndFileView.SetItemData(newItem, (DWORD_PTR)&data);
        data.hItem = newItem;

        if (data.lev == 0) hRoot = newItem;
    }

    m_wndFileView.Expand(hRoot, TVE_EXPAND);
}

void CFileView::InsertTreeNode(HTREEITEM hParent, FileTable& data)
{
    HTREEITEM newItem = m_wndFileView.InsertItem(data.name, hParent, TVI_LAST);
    m_wndFileView.SetItemData(newItem, (DWORD_PTR)&data);
    data.hItem = newItem;
}