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How to load a tree view with a large XML file

, 7 Jun 2000
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This article show you how to display very large XML in a tree view, and also shows you how to incorporate the MS XML parser in your app.
  • Download demo project - 50 Kb
  • Sample Image

    Introduction

    Recently I was required to display a very large XML file in a tree view, I tried to implement like "virtual list view" which displays whatever is visible in a view (when the user scrolls). After brainstorm and some web surfing I remembered windows explorer. I'm not sure how they implement it exactly but I guess they do same method as mine which expand any tree node on the fly i.e. don't populate the whole tree at start-up. If you don't do this, populate the whole tree for a 10 MB XML file size takes up to 45 minutes on a fast machine! doing my way will takes only approximately 3-5 seconds! The trick really is how to find out the relationship and info of any tree node and associated DOM node any where any time. To incorporate this into your app, either derive your class from CXmlTreeView or add appropriate message handlers and all helper methods to your own class.

    Note:

    • It'd be easier if you know how to incorporate XML parser into your app (this article uses Microsoft XML parser because of its available!), however, it's not a requirement.
    • You can apply the same method to any application-specific value instead of DOM node to populate a tree control
    • You can easily change this class to use as a tree control instead.

    The first you need to add a notify message handler for TVN_ITEMEXPANDING which notifies a tree view control's parent window that a parent item's list of child items is about to expand or collapse.

    void CXmlTreeView::OnItemexpanding(NMHDR*  pNMHDR, LRESULT* pResult) 
    {
        NM_TREEVIEW* pNMTreeView = (NM_TREEVIEW*)pNMHDR;
        HTREEITEM hItem = pNMTreeView->itemNew.hItem;
        MSXML::IXMLDOMElement* node = (MSXML::IXMLDOMElement*)GetTreeCtrl().GetItemData(hItem);
        HRESULT hr;
      
        *pResult = 0;
     
        // If m_bOptimizeMemory is false then we optimize by not adding and deleting 
        // already added items. The trade-off is memory exhausted!
      
        CWaitCursor waitCursor;     // This could take a while!
        GetTreeCtrl().LockWindowUpdate();
        if (pNMTreeView->action == TVE_EXPAND) 
        {
            if (m_bOptimizeMemory == FALSE) 
            {
                HTREEITEM hChildItem;
                if ((hChildItem = GetTreeCtrl().GetChildItem(hItem)) != NULL) 
                {
                   MSXML::IXMLDOMElement* childNode = 
                              (MSXML::IXMLDOMElement*) GetTreeCtrl().GetItemData(hChildItem);
                     
                   if (childNode == NULL)
                   {
                      GetTreeCtrl().DeleteItem(hChildItem);
                      MSXML::IXMLDOMNode* firstChild = NULL;
                      hr = node->get_firstChild(&firstChild);
                      if (SUCCEEDED(hr) && firstChild != NULL)
                      {
                          if (populateNode((MSXML::IXMLDOMElement*)firstChild, hItem) == FALSE) 
                          {
                              *pResult = 1; 
                          }                
                      }
                   }
                }
             } 
             else
             {
                 deleteFirstChild(hItem);
                 MSXML::IXMLDOMNode* firstChild = NULL;
                 hr = node->get_firstChild(&firstChild);
                 if (SUCCEEDED(hr) && firstChild != NULL) 
                 {
                     if (populateNode((MSXML::IXMLDOMElement*)firstChild, hItem) == FALSE) 
                     {
                         *pResult = 1; 
                     }
                 }
              }
          }
          else
          {
              // pNMTreeView->action == TVE_COLLAPSE
              if (m_bOptimizeMemory == TRUE) 
              {
                  deleteAllChildren(hItem);
                  // Set button state.
                  if (node->hasChildNodes()) 
                  {
                       int nImage, nSelectedImage;
                       nImage = nSelectedImage = getIconIndex(node);
                       HTREEITEM hChildItem = GetTreeCtrl().InsertItem(_T(""), nImage, 
                           nSelectedImage, hItem);
                       GetTreeCtrl().SetItemData(hChildItem, (DWORD)NULL);
                  }
              }
          }
          GetTreeCtrl().UnlockWindowUpdate();
      }
      

    The key in this function is the calls to GetItemData(..) and populateNode(..).

    • GetItemData(..) will retrieve the DOM node value associated with the specified item so we can use this DOM node to figure out the relationship with the rest.
    • populateNode(..) will only populate all siblings of the [in] node which is the child node of the current node.
    • m_bOptimizeMemory is used to optimize memory by delete all children when collapse or not. This value is set to false by default when you can loadXML(..).
    // This function populates all siblings of the
      [in] node.
      //
      BOOL CXmlTreeView::populateNode(MSXML::IXMLDOMElement *node, const HTREEITEM &hParent)
      {
          HRESULT hr = S_OK;
          BSTR nodeType, nodeName;
          HTREEITEM hItem;
      
          node->get_nodeTypeString(&nodeType);
          if (!wcscmp(nodeType, L"element")) {
              node->get_nodeName(&nodeName);
              hItem = insertItem(node, CString(nodeName), ILI_ELEMENT, ILI_ELEMENT, hParent);
              populateAttributes(node, hItem);
          } else if(!wcscmp(nodeType, L"text")) {
              node->get_text(&nodeName);
              hItem = insertItem(node, CString(nodeName), ILI_TEXT, ILI_TEXT, hParent); 
          } else if(!wcscmp(nodeType, L"comment")) {
              node->get_nodeName(&nodeName);
              hItem = insertItem(node, CString(nodeName), ILI_COMMENT, ILI_COMMENT, hParent); 
          } else {    // Handle more data types here if needed.
              node->get_nodeName(&nodeName);
              hItem = insertItem(node, CString(nodeName), ILI_OTHER, ILI_OTHER, hParent); 
          }
      
          MSXML::IXMLDOMNode* nextSibling = NULL;
          hr = node->get_nextSibling(&nextSibling);
          if (SUCCEEDED(hr) && nextSibling != NULL) {
              populateNode((MSXML::IXMLDOMElement*)nextSibling, hParent);
          }
      
          return TRUE;
      }
      

    The key in this function is the call to helper function insertItem(..) which set DOM node value associated with the specified tree item.

    HTREEITEM CXmlTreeView::insertItem(MSXML::IXMLDOMElement *node, 
          const CString &nodeName, int nImage, int nSelectedImage, 
          HTREEITEM hParent /*= TVI_ROOT*/, HTREEITEM hInsertAfter /*= TVI_LAST*/)
      {
          HTREEITEM hItem = GetTreeCtrl().InsertItem(nodeName, nImage, 
              nSelectedImage, hParent, hInsertAfter); 
          GetTreeCtrl().SetItemData(hItem, (DWORD)node);
      
          // Set button state.
          if (node->hasChildNodes()) {
              HTREEITEM hChildItem = GetTreeCtrl().InsertItem(_T(""), nImage, 
                   nSelectedImage, hItem);
              GetTreeCtrl().SetItemData(hChildItem, (DWORD)NULL);
          }
      
          return hItem;
      }
      
      

    Please don't send emails but post here if you have any questions regarding this article.

    License

    This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

    A list of licenses authors might use can be found here

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    About the Author

    Frank Le

    United States United States
    No Biography provided

    Comments and Discussions

     
    GeneralA better way PinmemberMember 40403951-Jul-09 15:03 
    Generallicense Pinmemberavirabinovich19-May-09 5:36 
    QuestionIn C# PinmemberPrateek Bahl2-Jul-08 10:06 
    AnswerRe: In C# PinmemberPrateek Bahl18-Sep-08 5:03 
    QuestionIntegration with other classes PinmemberNilson Bastos Jr1-Apr-08 10:59 
    GeneralIn VB.net 2005 PinmemberShailShin11-Jun-06 22:37 
    GeneralNice, but memory leak... PinmembereXRange16-Aug-05 17:44 
    If you load some XML files many times, you can see from TaskManager that the program has already consumed a lot of memory.
    Because in you code ,you didn't call Release() after using COM interface pointers.
    Using smart pointer wrapper classes like IXMLDOMDocumentPtr will fix the problem. And using exception handling will make code easier to read.
     
    Best Regards
     
    eXMe

    GeneralAnother Memory Leak PinmemberStellar Developer30-Jun-05 8:01 
    GeneralRe: Another Memory Leak Pinmemberpocjoc12-Jul-05 22:40 
    Generalsuggestion PinmemberChauJohnthan7-Apr-05 11:17 
    GeneralSDI to MDI Pinmemberhelp_cplus17-Nov-04 1:58 
    GeneralMemory Leak Pinmembermistretzu27-Sep-04 3:07 
    GeneralMemory Leak PinsussAnonymous27-Sep-04 3:03 
    GeneralDynamic updating of tree with new data PinmemberJRubinstein19-Aug-04 8:27 
    GeneralRe: Dynamic updating of tree with new data PinsussAnonymous19-Aug-04 12:30 
    GeneralRe: Dynamic updating of tree with new data PinmemberJRubinstein19-Aug-04 15:24 
    GeneralDTD Schema PinmemberBruno II20-Oct-03 3:29 
    GeneralThe demo project is corrupted PinmemberTW16-Feb-03 23:47 
    GeneralLoading an XML file initially PinmemberChris Hunter17-Oct-02 1:16 
    Generalxml diff PinmemberMurari28-Jun-02 9:30 
    GeneralRe: xml diff PinsussAnonymous19-Aug-04 12:33 
    GeneralModified it to work with the Pocket PC Pinmembermark edwards24-Jan-02 9:25 
    GeneralRe: Modified it to work with the Pocket PC PinmemberFrank Le11-Mar-02 10:07 
    GeneralRe: Modified it to work with the Pocket PC Pinmembernishu5-Aug-02 10:10 
    GeneralA way of study Pinmemberswitch wang4-Sep-01 23:12 

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