VB.Net，XPath和XMLReader - 下一個和上一個記錄

Question

下面的VB.Net代碼在移動到xml文件（sampler_01.xml）中的下一條記錄方面工作正常。如您所見，VB.Net代碼使用XPath。我遇到的問題是獲取任何邏輯與「上一個」按鈕（btnPrevious）一起工作並獲取以前的記錄。

我真正想要做的是有能力移動到一個記錄旁邊或移回到先前的記錄。在這一點上，我不確定如何應用邏輯。任何建議或幫助將不勝感激。

謝謝！

編輯：請參考下面以 「Form1.vb的2.0」

「sampler_01.xml」

<?xml version="1.0" encoding="UTF-8"?> 
<Companies> 
    <Company Id="000001"> 
     <CompID>000001</CompID> 
     <ContFn>Jerry</ContFn> 
     <ContLn>McGuire</ContLn> 
     <ContEmail>jerrym@email.com</ContEmail> 
     <ContPhone>(603) 555-1212</ContPhone> 
    </Company> 
    <Company Id="000002"> 
     <CompID>000002</CompID> 
     <ContFn>Ben</ContFn> 
     <ContLn>Henderson</ContLn> 
     <ContEmail>benh@email.com</ContEmail> 
     <ContPhone>(603) 882-4040</ContPhone> 
    </Company> 
    <Company Id="000003"> 
     <CompID>000003</CompID> 
     <ContFn>Bob</ContFn> 
     <ContLn>James</ContLn> 
     <ContEmail>bobj@email.com</ContEmail> 
     <ContPhone>(603) 641-2120</ContPhone> 
    </Company> 
    <Company Id="000004"> 
     <CompID>000004</CompID> 
     <ContFn>Aaron</ContFn> 
     <ContLn>Smith</ContLn> 
     <ContEmail>arrons@email.com</ContEmail> 
     <ContPhone>(603) 968-1212</ContPhone> 
    </Company> 
</Companies> 

「Form1.vb的1.0」

Imports System.Net 
Imports System.IO 
Imports System.Xml 
Imports System.Xml.XPath 

    Public Class Form1 

    Dim xpd As XPathDocument 
    Dim xpn As XPathNavigator 
    Dim xpn1, xpn2, xpn3, xpn4, xpn5 As XPathNodeIterator 

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load 

    LoadXmlToRead() 

    End Sub 

    Private Sub ListToTextBoxes() 

    txtCompID.Text = xpn1.Current.Value 
    txtContFn.Text = xpn2.Current.Value 
    txtContLn.Text = xpn3.Current.Value 
    txtContEmail.Text = xpn4.Current.Value 
    txtContPhone.Text = xpn5.Current.Value 

    End Sub 

    Private Sub LoadXmlToRead() 

    xpd = New XPathDocument("C:\XML_Files\sampler_01.xml") 
    xpn = xpd.CreateNavigator() 

    xpn1 = xpn.Select("/Companies/Company/CompID") 
    xpn2 = xpn.Select("/Companies/Company/ContFn") 
    xpn3 = xpn.Select("/Companies/Company/ContLn") 
    xpn4 = xpn.Select("/Companies/Company/ContEmail") 
    xpn5 = xpn.Select("/Companies/Company/ContPhone") 

    End Sub 

    Private Sub btnNext_Click(sender As System.Object, e As System.EventArgs) Handles btnNext.Click 

    If xpn1.MoveNext() Or _ 
     xpn2.MoveNext() Or _ 
     xpn3.MoveNext() Or _ 
     xpn4.MoveNext() Or _ 
     xpn5.MoveNext() Then 
     ListToTextBoxes() 
    Else 

    MsgBox("End of contacts has been reached...") 
     LoadXmlToRead() 
    End If 

    End Sub 

    Private Sub btnLoad_Click(sender As System.Object, e As System.EventArgs)Handles btnLoad.Click 

    LoadXmlToRead() 

    If txtCompID.Text = "" And _ 
     txtContFn.Text = "" And _ 
     txtContLn.Text = "" And _ 
     txtContLn.Text = "" And _ 
     txtContPhone.Text = "" Then 

     xpn1.MoveNext() 
     xpn2.MoveNext() 
     xpn3.MoveNext() 
     xpn4.MoveNext() 
     xpn5.MoveNext() 

     ListToTextBoxes() 

     MsgBox("The Contact database has been loaded") 
    End If 

    End Sub 

    Private Sub btnPrevious_Click(sender As System.Object, e As System.EventArgs) Handles btnPrevious.Click 

    If xpn1.Current.MoveToPrevious() Or _ 
     xpn2.Current.MoveToPrevious() Or _ 
     xpn3.Current.MoveToPrevious() Or _ 
     xpn4.Current.MoveToPrevious() Or _ 
     xpn5.Current.MoveToPrevious() Then 

     ListToTextBoxes() 

    End If 

    End Sub 
End Class 

Answer 1

Th下面的代碼使用XML Reader可以有效地處理我需要的東西。在用Linq進行了一些測試之後（正如jdweng雄辯地提出的那樣），我發現在一些重新設計之後，XML Reader是讀取1MEG以外的更大XML文件的更好選擇。下面的代碼處理上一個和下一個控件，同時在讀取XML文件時捕獲任何更新。

「Form1.vb的2.0」

Imports System.IO 
Imports System.Xml 

Public Class Form1 

     Public dSet = New DataSet 
     Public CompRow As Integer 

     Private Sub FileLoad() 

      dSet.Clear() 

      Dim xmlFile As XmlReader 
      xmlFile = XmlReader.Create("C:\XML_Files\sampler_01.xml", New XmlReaderSettings()) 
      dSet.ReadXml(xmlFile) 

      CompRow = 0 
      ShowData(CompRow) 

      xmlFile.Close() 

     End Sub 

     Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load 

      FileLoad() 

     End Sub 

     Private Sub btnReLoad_Click(sender As System.Object, e As System.EventArgs) Handles btnReLoad.Click 

      FileLoad() 

     End Sub 

     Private Sub ShowData(ByVal CurrentRow) 

      txtCompID.Text = dSet.Tables("Company").Rows(CompRow)("CompID").ToString 
      txtContFn.Text = dSet.Tables("Company").Rows(CompRow)("ContFn").ToString 
      txtContLn.Text = dSet.Tables("Company").Rows(CompRow)("ContLn").ToString 
      txtContEmail.Text = dSet.Tables("Company").Rows(CompRow)("ContEmail").ToString 
      txtContPhone.Text = dSet.Tables("Company").Rows(CompRow)("ContPhone").ToString 

     End Sub 

     Private Sub btnNext_Click(sender As System.Object, e As System.EventArgs) Handles btnNext.Click 

      If CompRow <> dSet.Tables("Company").Rows.Count - 1 Then 
       CompRow += 1 
       ShowData(CompRow) 
      Else 
       MsgBox("Last Record is Reached!!!") 
      End If 

     End Sub 

     Private Sub btnPrevious_Click(sender As System.Object, e As System.EventArgs) Handles btnPrevious.Click 

      If CompRow <> 0 Then 
       CompRow -= 1 
       ShowData(CompRow) 
      Else 
       MsgBox("First Record is Reached!!!") 
      End If 

     End Sub 
End Class 

Answer 2

使用XML我更新的答案linq

Imports System.Xml 
Imports System.Xml.Linq 
Public Class Form1 

    Const FILENAME As String = "c:\temp\test.xml" 

    Sub New() 

     ' This call is required by the designer. 
     InitializeComponent() 

     ' Add any initialization after the InitializeComponent() call. 
     Dim doc As XDocument = XDocument.Load(FILENAME) 

     Dim companies = doc.Descendants("Company").ToList() 

     Dim companyPointer = companies.First() 

     Dim index As Integer = 0 
     companyPointer = companies(index + 1) 
     index = index + 1 


    End Sub 

End Class 
​