如何从VB中的文本文件中读取特定行

Question

我正在创建一个程序,应该将文本写入文本文件,并且应该能够从VB中的文本文件中读取特定的行(所以如果我需要读取特定的名称,我可以选择第5行,它将显示在文本框).我能够从文本文件中读取文本,但我不知道如何控制特定的行.

这是我的代码:

Public Class Form1

    Private Sub btnSubmit_Click(sender As System.Object, e As System.EventArgs) Handles btnSubmit.Click
         Dim writer As New System.IO.StreamWriter("/text.txt", True)
         writer.WriteLine(txtFirstName.Text)
         writer.WriteLine(txtLastName.Text)
         writer.WriteLine("-------------------------------------")
         writer.Close()
    End Sub

     Private Sub btnRead_Click(sender As System.Object, e As System.EventArgs) Handles btnRead.Click
        Dim reader As New System.IO.StreamReader("/text.txt")
        Dim FirstName, LastName As String
        FirstName = reader.ReadLine()
        LastName = reader.ReadLine()
        reader.Close()
        txtFirstName.Text = FirstName
        txtLastName.Text = LastName
    End Sub

    Private Sub btnClear_Click(sender As System.Object, e As System.EventArgs) Handles btnClear.Click
        txtFirstName.Clear()
        txtLastName.Clear()
    End Sub
End Class

任何帮助,将不胜感激.谢谢!

Answer 1

您必须阅读所有您感兴趣的行.例如:

Function ReadLineWithNumberFrom(filePath As String, ByVal lineNumber As Integer) As String
    Using file As New StreamReader(filePath)
        ' Skip all preceding lines: '
        For i As Integer = 1 To lineNumber - 1
            If file.ReadLine() Is Nothing Then
                Throw New ArgumentOutOfRangeException("lineNumber")
            End If
        Next
        ' Attempt to read the line you're interested in: '
        Dim line As String = file.ReadLine()
        If line Is Nothing Then
            Throw New ArgumentOutOfRangeException("lineNumber")
        End If
        ' Succeded!
        Return line 
    End Using
End Function

这是因为文本行是可变长度记录,并且无法猜测特定行开始处的确切文件偏移量 - 而不是没有索引.

如果您经常需要加载特定的行,您还有更多选择:

• 将完整的文本文件加载到内存中,例如使用File.ReadAllLines("Foobar.txt").这将返回一个String()数组,您可以通过行号直接访问该数组.

• 手动创建行号索引.也就是说,逐行处理文本文件,并随时填写Dictionary(Of Integer, Integer).键是行号,值是文件偏移量.这使您可以.Seek直接到特定行的开头,而无需将整个文件保留在内存中.

Answer 2

尝试这个：

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    Dim reader As New System.IO.StreamReader("C:\text.txt")
    Dim allLines As List(Of String) = New List(Of String)
    Do While Not reader.EndOfStream
        allLines.Add(reader.ReadLine())
    Loop
    reader.Close()
    txtFirstName.Text = ReadLine(5, allLines)
    txtLastName.Text = ReadLine(6, allLines)

End Sub

Public Function ReadLine(lineNumber As Integer, lines As List(Of String)) As String
    Return lines(lineNumber - 1)
End Function

如果你有这样的文件：

Line 1
Line 2
Line 3
Line 4
My Name
My LastName

您的姓名文本框将包含“我的名字”，而您的姓氏文本框将包含“我的姓氏”。