Ñïîñîáû ïåðåõîäà XML ñ ïîìîùüþ êëàññà XPathNavigator, èñïîëüçóÿ Visual Basic

Òðåáîâàíèÿ

• Microsoft Windows Server 2003, Microsoft Windows 2000 Professional, Windows 2000 Server, Windows 2000 Advanced Server èëè Microsoft Ñåðâåð Windows NT 4.0
• Visual Studio Microsoft 2005 èëè Microsoft Visual Studio .NET

• Òåðìèíîëîãèÿ XML.
• Ñîçäàíèå è ÷òåíèå XML-ôàéëîâ
• Ñèíòàêñèñ ÿçûêà XML Path (XPath)

Èñïîëüçîâàíèå êëàññà XPathNavigator äëÿ ïåðåìåùåíèÿ XML

1. Â 2005 ã. Visual Studio èëè Visual Studio. NET, ñîçäàíèå 2005 Visual Basic èëè Visual Basic .NET êîíñîëüíîãî ïðèëîæåíèÿ.
   
   Ïðèìå÷àíèå  ýòîì ïðèìåðå èñïîëüçóåòñÿ ôàéë ñ èìåíåì Books.xml. Ìîæíî ñîçäàòü ôàéë Books.xml èëè èñïîëüçîâàòü îáðàçåö, êîòîðûé âõîäèò â ñîñòàâ Ïðèìåðû èñïîëüçîâàíèÿ êîìïëåêò SDK äëÿ ðàçðàáîòêè ïðîãðàììíîãî îáåñïå÷åíèÿ .NET. Åñëè ó âàñ åñòü ïðèìåðû èñïîëüçîâàíèÿ óñòàíîâêè Books.xml íàõîäèòñÿ â ñëåäóþùåé ïàïêå:
   \Program Files\Microsoft.NET\FrameworkSDK\Samples\Quickstart\Howto\Samples\Xml\Transformxml\VB
   Êðîìå òîãî, Ýòîò ôàéë ìîæíî ïîëó÷èòü, ïîñåòèâ ñëåäóþùèé âåá-óçåë:
   .aspx http://MSDN.Microsoft.com/en-us/library/Windows/Desktop/ms762271 (v=vs.85)

   (http://msdn.microsoft.com/en-us/library/windows/desktop/ms762271(v=vs.85).aspx)
   
   Íåîáõîäèìî ñêîïèðîâàòü ôàéë Books.xml â Ïàïêó \bin\Debug, ðàñïîëîæåííûé â ïàïêå, â êîòîðîì ñîçäàíà ýòà ïðîåêò.
2. Óáåäèòåñü, ÷òî ïðîåêò ññûëàåòñÿ íà ïðîñòðàíñòâî èìåí System.Xml .
3. Èñïîëüçîâàòü îïåðàòîð Imports äëÿ ïðîñòðàíñòâ èìåí Xml è XPath , òàêèì îáðàçîì, íå òðåáóåòñÿ óêàçûâàòü îáúÿâëåíèÿ â ýòèõ ïðîñòðàíñòâàõ èìåí â êîäå. Íåîáõîäèìî èñïîëüçîâàòü îïåðàòîð Imports ïåðåä âñåìè îñòàëüíûìè îáúÿâëåíèÿìè.

   Imports System.Xml
   Imports System.Xml.XPath
   					

4. Îáúÿâèòå ñîîòâåòñòâóþùèõ ïåðåìåííûõ. Îáúÿâèòå îáúåêò XPathDocument äëÿ õðàíåíèÿ XML-äîêóìåíò è îáúåêò XPathNavigator äëÿ âû÷èñëåíèÿ âûðàæåíèé XPath è ïåðåìåùåíèÿ ïî äîêóìåíò. Îáúÿâèòå ñòðîêîâûé îáúåêò äëÿ âûðàæåíèÿ XPath. Äîáàâüòå êîä â îáúÿâëåíèå ïðîöåäóðà Main â Module1.

   Dim nav As XPathNavigator
   Dim docNav As XPathDocument
   					

5. Çàãðóçèòå îáúåêò XPathDocument â ïðèìåðå ôàéë Books.xml. Êëàññ XPathDocument èñïîëüçóåò ïðåîáðàçîâàíèÿ ðàñøèðÿåìîãî ÿçûêà ñòèëåé (XSLT) äëÿ îáåñïå÷åíèÿ áûñòðîãî è ïðîèçâîäèòåëüíîñòè êýøà äëÿ îáðàáîòêè XML-äîêóìåíòîâ. Àíàëîãè÷íî äëÿ ìîäåëè îáúåêòîâ äîêóìåíòà XML (DOM), íî çíà÷èòåëüíî îïòèìèçèðîâàí äëÿ îáðàáîòêè XSLT è ìîäåëè äàííûõ XPath.

   'Open the XML.
   docNav = New XPathDocument("books.xml")
   					

6. Ñîçäàéòå îáúåêò XPathNavigator èç äîêóìåíòà. XPathNavigator èñïîëüçóåòñÿ äëÿ ïåðåìåùåíèÿ ïî óçëàì àòðèáóòîâ è óçëû ïðîñòðàíñòâ èìåí â XML-äîêóìåíòå.

   'Create a navigator to query with XPath.
   nav = docNav.CreateNavigator
   					

7. Ïåðåìåùåíèå êîðíåâîãî äîêóìåíòà ñ ïîìîùüþ ìåòîäà MoveToRoot . MoveToRoot çàäàåò íàâèãàòîð íà óçåë äîêóìåíòà, êîòîðûé ñîäåðæèò âåñü äåðåâî óçëîâ.

   'Initial XPathNavigator to start at the root.
   nav.MoveToRoot()
   					

8. Èñïîëüçóéòå ìåòîä MoveToFirstChild äëÿ ïåðåìåùåíèÿ äëÿ äî÷åðíèõ XML-äîêóìåíòà. Ìåòîä MoveToFirstChild ïåðåìåùàåò ïåðâûé äî÷åðíèé ýëåìåíò òåêóùåãî óçëà.  ñëó÷àå èñòî÷íèêà Books.xml ïðè ïåðåìåùåíèè îò êîðíåâîãî äîêóìåíòà â äî÷åðíèå ýëåìåíòû, â ðàçäåëå êîììåíòàðèåâ è óçåë Bookstore.

   'Move to the first child node (comment field).
   nav.MoveToFirstChild()
   					

9. Ñ ïîìîùüþ ìåòîäà MoveToNext èòåðàöèþ óçëîâ íà óðîâíå òîãî æå óðîâíÿ. Ïåðåìåùåíèå ìåòîäà MoveToNext ñëåäóþùèé îäíîóðîâíåâûé ýëåìåíò òåêóùåãî óçëà.

   'Loop through all the root nodes.
   Do
       ...
   Loop While nav.MoveToNext
   					

10. Óáåäèòåñü, ÷òî òîëüêî îáðàáîòêå óçëîâ ýëåìåíòà ñëåäóåò èñïîëüçîâàòü ñâîéñòâî NodeType è èñïîëüçîâàòü ñâîéñòâî Value äëÿ îòîáðàæåíèÿ ïðåäñòàâëåíèÿ òåêñòà ýëåìåíòà.

    Do
        'Find the first element.
        If nav.NodeType = XPathNodeType.Element Then
    'If children exist.
    If nav.HasChildren Then
    
        'Move to the first child.
        nav.MoveToFirstChild()
    
        'Loop through all the children.
        Do
    'Display the data.
    Console.Write("The XML string for this child ")
    Console.WriteLine("is '{0}'", nav.Value)
    Loop While nav.MoveToNext
    
    End If
        End If
    Loop While nav.MoveToNext
    					

11. ×òîáû îïðåäåëèòü íàëè÷èå àòðèáóòîâ ó óçëà ñ ïîìîùüþ ñâîéñòâà HasAttributes âûïîëíÿåòñÿ . Âû ìîæåòå òàêæå ìîæíî èñïîëüçóéòå äðóãèå ìåòîäû, íàïðèìåð MoveToNextAttribute, äëÿ ïåðåìåùåíèÿ àòðèáóòà è ïðîâåðÿòü åãî çíà÷åíèå. Îáðàòèòå âíèìàíèå, ýòî ñåãìåíò êîäà ïðîõîäèò òîëüêî ÷åðåç ïîòîìêè êîðíåâîãî óçëà è íå âñåãî äåðåâà.

    Do
        'Find the first element.
        If nav.NodeType = XPathNodeType.Element Then
    'if children exist
    If nav.HasChildren Then
    
        'Move to the first child.
        nav.MoveToFirstChild()
    
        'Loop through all the children.
        Do
    'Display the data.
    Console.Write("The XML string for this child ")
    Console.WriteLine("is '{0}'", nav.Value)
    
    'Check for attributes.
    If nav.HasAttributes Then
        		Console.WriteLine("This node has attributes")
    End If
    Loop While nav.MoveToNext
    
    End If
        End If
    Loop While nav.MoveToNext
    					

12. Äîáàâèòü ïàóçó â êîíöå îòîáðàæåíèÿ êîíñîëè áîëåå ñ ïîìîùüþ ìåòîäà ReadLine îáúåêòà êîíñîëè ëåãêî îòîáðàæàòü ðåçóëüòàòû âûøå.

    'Pause.
    Console.ReadLine()
    					

13. Ïîñòðîåíèå è çàïóñê ïðîåêòà êîíñîëüíîãî ïðèëîæåíèÿ.

Ïîëíûé ïðèìåð êîäà

Imports System.Xml
Imports System.Xml.XPath

Module Module1

    Sub Main()
        Dim nav As XPathNavigator
        Dim docNav As XPathDocument
        docNav = New XPathDocument("books.xml")
        nav = docNav.CreateNavigator
        nav.MoveToRoot()
        'Move to the first child node (comment field).
        nav.MoveToFirstChild()

        Do
            'Find the first element.
            If nav.NodeType = XPathNodeType.Element Then
                'if children exist
                If nav.HasChildren Then

                    'Move to the first child.
                    nav.MoveToFirstChild()

                    'Loop through all the children.
                    Do
                        'Display the data.
                        Console.Write("The XML string for this child ")
                        Console.WriteLine("is '{0}'", nav.Value)

                        'Check for attributes.
                        If nav.HasAttributes Then
                            Console.WriteLine("This node has attributes")
                        End If
                    Loop While nav.MoveToNext

                End If
            End If
        Loop While nav.MoveToNext

        'Pause.
        Console.ReadLine()

    End Sub

End Module
				

Ïåðåéòè ê íà÷àëó ñòðàíèöû | Îòïðàâèòü îòçûâ